Alvand Cable Tray & Cable Ladder Catalogue

HOW TO SELECT

THE TRAY FOR YOUR SITE / TERMS & CONDITIONS / DEFINITIONS

TECHNICAL INFORMATION

ALVAND Cable Tray & Ladder Co.

http://www.alvand-co.com/

mailto:[email protected]

www.alvand-co.com / [email protected] / +98(21) 22 64 6197 – 8

HOW TO SELECT CABLE TRAY

A lot of thought must go into choosing and installing cable trays in

order to ensure the safety and effectiveness of the cables that run

through them. Those systems ensure the effectiveness of the cables

they protect, reduce wear and tear to rooftop installations, and help

ensure safety for people, as well as, property.

1) Use Cable Trays!

The first and most obvious of these best practices is that you should

always use cable trays. Commercial rooftops typically have a

number of different types of cables running across them, carrying

high and low-voltage electrical current to meet power and

communication needs.

It's important to protect both the cables themselves, as well as, the

insulation around them. Don't let cables sag between trays, as that

can cause wear and tear and eventual damage. It's also crucial to

protect the insulation, which is best done by de-energizing cables during installation. That way, all parts of the rooftop

installation are protected, not just the cables themselves.

2) Include Expansion Joints at the Appropriate Intervals

Cable tray expansion joints help ensure the effectiveness of cable trays despite the wide range of temperatures that

exist. Burning heat and icy cold cause expansions and contractions of trays, which can cause them to tear loose from

their cable tray supports if you don’t use expansion joints. An expansion joint is the place where two trays meet, and

are connected along the connector plate, along which each tray can move inward or outward, depending on

temperature. The two trays are attached to one another using a strip that can stretch or retract in response to

temperature as well. For your specific application, be sure to consult this handy guide from the alvand Cable Tray.

3) Implement Proper Spacing For Cable Tray Supports

A number of factors implement the spacing for cable tray supports, including the material of the tray, the highest and

lowest temperatures the rooftop will likely encounter, and the temperature at the time of installation. The cable tray

support must be located no less than 2 feet from each side of the expansion joint splice plates position, allow the cable

tray to expand without distortion, be anchored at the support closest to the midpoint, and allow trays to expand and

contract in respond to temperature shifts. Consult the guide listed above for more information.

4) Consider Your Application Before Purchasing Cable Trays

Cable trays aren’t made to support just any type of line. Water and compressed air tubing, for instance, cannot be

supported by cable trays. According to the Cable Tray Institute, “NEC section 300.8 does not permit any tube, pipe,

or equal for water, air gas, drainage, steam, or any service other than electrical in raceways or cable trays containing

electrical conductors.” Rather, they are meant only to support power, signal, communication and optical fiber cables

only. Also, there are NEC rules dictating how each of these cable types must be segregated, either by dividers within

the tray or by separate trays. This helps reduce noise and interference from other cables.

Installing cable trays according to best practices isn’t difficult, but it does take expert knowhow. If you’re looking for

innovative, high-performance rooftop pipe and equipment support systems, or information about them, you’ve come

to the right place. Here at PHP Systems/Design, that’s exactly what we do. Get in touch today to learn more.

Do it





Technical Bulletins

ALVAND has committed most of its energies towards support services.

The Cable Tray Institute is now making available our complete library of technical articles which have appeared in

the Cablegram.

Titles available:

1 - Paralleled Phase Conductors in Cable Trays Provide Copper Savings

2 - Thermal Contraction and Expansion of Cable Tray

3 - Moisture Problems in Electrical Systems

4 - Cable Tray Type Selection

5 - Tie down Practices for Multi conductor Cables in Cable Trays

6 - Circuit Integrity of Cable Tray Wiring Systems during Natural Disasters

7 - Caution in Using Cable Tray Covers Outdoors

8 - Bonding Jumpers Not Required for Standard Cable Tray Splice Plates

9 - Cable Tray Wiring Systems Have Many Cost Advantages

10 - Cable Tray Systems in Ducts, Plenums and Other Air Handling Space

11 - Equipment Grounding Conductors for Cable Tray Systems

12 - Grounding Inspection of Steel & Aluminum Cable Tray Systems

13 - Hot Dip Galvanized vs. Aluminum in Outdoor Application

14 - Cable Tray Width Selection for Installation with 600 Volt Single Conductor Cables

15 - Cable Tray Grounding: Power, Instrumentation, and Telecommunications

16 - Types of Cabling Used in Cable Tray





1 - Paralleled Phase Conductors in Cable Trays Provide Copper Savings

Cable tray wiring systems have conductor advantages over conduit wiring systems where the installations involve

phase conductors installed in parallel.

For large ampacity circuits, the most practical wiring system installations are those where reasonable size conductors

are paralleled for each phase to adequately handle the circuit’s ampere requirements. A more efficient use of conductor

material is made by paralleling phase conductors than by using very large single conductors per phase.

A 500 ampere – 480 volt three phase 600 feet long feeder that is installed where it is sometimes exposed to moisture

and where the maximum ambient temperature is 110 degrees Fahrenheit is a practical circuit to use as an example. A

good conductor choice for such a circuit would be 75 degree Celsius rated XHHW OR THHN/THWN insulated

copper conductors as per 2005 NEC Ampacity Table 310-16. The ambient temperature ampacity correction adjusts

the 500 ampere circuit Ampacity requirement to 610 amperes. (500 amperes / 0.82 = 610 amperes).

For the installation described above:

A conduit wiring system would require 6 – 500 kcmil conductors which contain 5558 pounds of copper.

A cable tray wiring system would require 6 – 350 kcmil conductors which contain 3892 pounds of copper.

The cable tray wiring system uses 1666 pounds less copper for the same capacity circuit than the conduit wiring

system does plus there are installation cost savings available by using a cable tray wiring system instead of a conduit

wiring system. This evaluation assumes that both the conduit and the cable tray are serving as the equipment

grounding conductor. Where separate equipment grounding conductors are used, the copper savings values will be

different than those stated above. See the details below for additional information.

1- Details for a Conduit Installation:

The ampacity adjustment factor for 6 conductors (2 conductors per phase) in the same conduit adjusts the circuit

ampacity requirement to 763 amperes. (610 amperes/0.8 =763 amperes).

Size of the conductors required is 500 kg mil. (763 amperes/2 conductors per phase = 382 amperes 500 kg mil XHHW

or THHN/ THWN insulated copper conductor’s maximum ampacity rating is 380 amperes). Pulling large cables into

conduits subjects the insulation to abrasion. For this type of installation, the XHHW insulation is preferred due to its

superior mechanical characteristics over those of the THHN/THWN insulation.

The copper conductor material for this installation is 5558 pounds. (1.544 lbs/ft x 600 feet x 6 conductors = 558

pounds).

The equipment grounding conductor options available for this type of installation are as follows: Cable trays Institute

Technical Bulletin http://www.alvand-co.com.com/techbul1.htm 2 of 3 C1. The conduit may serve as the equipment

grounding conductor.





C2. A separate #2 AWG equipment grounding conductor may be installed in the conduit if the owner does not desire

to use the conduit as the equipment grounding conductor. 2005 NEC Table 250.122 specifies a #2 AWG copper

equipment grounding conductor for a 500 ampere protective device rating or setting. For a #2 AWG equipment

grounding conductor 123 pound of copper is required. (0.205 lbs/ft x 600 feet = 123 pounds).

1. Details for a Cable Tray Installation with Multi conductor Cables (3 THHN/THWN insulated copper

conductors with a PVC jacketed cable):

No ampacity adjustment factor correction is required for three conductor cables paralleled in cable tray. See 2005

NEC Section 392.11(A) (1) Size of the conductors required is 350 kcmil [610 amperes/2 conductors per phase (two

– three conductor cables required) = 305 amperes – a 350 kcmil THHN/THWN insulated copper conductor’s

maximum ampacity rating is 310 amperes.


pounds)

The equipment grounding conductor options available for this type of installation are as follows: M1. The cable tray

may be used as the equipment grounding conductor for qualifying commercial and industrial installations as per 2005

NEC Section 392.3© M2. #2 AWG copper equipment grounding conductors may be in the three conductor cables. If

this is done, a fully rated equipment grounding conductor must be in each cable as per 2005NEC Section 250.122.

For this case 246 pounds of copper is required. (0.205 lbs/ft. x 600 feet x 2 = 246 o-pounds).

M3. A single #2 AWG copper equipment grounding, conductor may be installed in or on the cable tray. For this case

123 pounds of copper is required. (0.205 lbs/ft x 600 feet = 123 pounds).

2. Details for a Cable Tray Installation with Single Conductor Cables:

This type of installation is restricted to qualifying industrial installations as per 1993 NEC Section 392.3(B).

Installation must comply with 2005 NEC Section) 392.8(D) Connected in Parallel.

Size of the conductors required is 350 kcmil. As per 2005 NEC Section 392.11 (B) (2) Ampacity values are limited

to 0.65 percent of the values indicated in 2005 NEC Table 310-17. [610 amperes/ 2 conductors per phase = 305

amperes – a 350 kcmil 75 degree Celsius rated XHHW or THHN/ THWN insulated copper conductor’s maximum

ampacity rating in 1993 Table 310-17 is 505 amperes. 505 amperes x 0.65 = 328 amperes so 350 kcmil is the size of

conductor that must be selected to carry 310 amperes.


pounds)

The equipment grounding conductor options available for this type of installation are as follows:

S1. The cable tray may be used as the equipment grounding conductor as per 1993 NEC Section 392.3©





S2. A single #2 AWG copper equipment grounding conductor may be installed in or on the cable tray for this case

123 pounds of copper is required. (0.205 lbs/ft x 600 ft = 123 pounds).

2- Thermal Contraction and Expansion of Cable Tray

All materials expand and contract due to temperature changes. It is important that cable tray installations incorporate

features which provide adequate compensation for their thermal contraction and expansion.

1993 NEC Section 300-7 (b) states that “Raceways shall be provided with expansion joints where necessary to

compensate for the thermal expansion or contraction.” In 1993 NEC Article 318 there are no requirements for the

handling of the thermal contraction and expansion of cable tray. This subject is addressed in the NEMA Standards

Publication No. VE 1 “Metallic Cable Tray Systems” Section 6.8.

There are expansion joint splice plates and bonding jumpers available from cable tray manufacturers. A cable tray

support should be located within 2 feet of each side of the expansion joint splice plate’s position. The cable trays must

not be clamped to each support so firmly that the cable tray cannot expand without distortion. The cable tray needs to

be anchored at the support closest to the midpoint between the expansion joints with hold down clamps and secured

by expansion guides at all other support locations. The expansion guides allow the cable tray to slide back and forth

as it contracts and expands. If provisions for the thermal contraction and expansion of the cable trays are not provided

for where there are large summer to winter temperature extremes (example: roof top installations); there is the

potential for the cable trays to tear loose from their supports, for the cable trays to bend (snake), or for bolt hole

elongations at the splice plate areas.

Bridges and some other structures have expansion joints. Installing expansion joints in the cable tray runs only at the

structure expansion joint positions, does not normally provide a valid solution to adequately compensate for the cable

tray’s thermal contraction and expansion. The materials of the structures and the cable trays are different. They will

have different values of thermal contraction and expansion. They each require unique solutions for their thermal

compensation and expansion.

In the NEMA Metallic Cable Tray Systems Standard VE 1, Section 6.8 Thermal Contraction and Expansion. VE 1

Table 6-1 shows the allowable lengths of steel and aluminum cable tray between expansion joints for the temperature

differential values.

For a 100° F differential (winter to summer), a steel cable tray will require an expansion joint every 128 feet and an

aluminum cable tray every 65 feet. The temperature at the time of installation will dictate the gap setting.

VE 1 Figure 6-9 is a monograph from which the required metal expansion gap setting may be determined.





The Gap Setting of the Expansion Joint Splice Plate Monograph is used as follows per the example indicated on VE

1 Figure 6-9.

Step 1. Plot the highest expected cable tray metal temperature on the maximum temperature vertical axis. Example’s

Value = 100° F.

Step 2. Plot the lowest expected cable tray metal temperature on the minimum temperature vertical axis. Example’s

Value: = -28° F.

Step 3. Draw a line between these maximum and minimum temperature points on the two vertical axis.

Step 4. To determine the required expansion joint gap setting: Plot the cable tray metal temperature at the time of the

cable tray installation on the Maximum temperature vertical axis (Example’s Value: 50° F). Project over from the 50°

F point on the maximum temperature vertical axis to an intersection with the line between the maximum and minimum

cable tray metal temperatures. From this intersection point, project down to the gap setting horizontal axis to find the

correct gap setting value (Example’s Value: 3/8 inch gap setting). This is the length of the gap to be set between the

cable tray sections at the expansion joint splice plate location.

For simplicity, the bonding jumpers around the expansion joint splice plates should be sized to match the fault current

capacity of the cable tray side rails or the cable tray cross section for one piece construction cable trays. Following

such a practice will not require that the bonding jumpers must be changed if higher capacity circuits (that require

increases in the protective device sizes or setting) are installed in the cable tray at a later date. If it is known that there

will not be any additions of higher rated circuits and that the rating of the protective devices will not be increased, the

bonding jumpers may be sized as per 1993 NEC Table 250-95.





3- Moisture Problems in Electrical Systems

When selecting a facilities wiring system, the potential for the wiring system to allow moisture to flow into the

electrical equipment enclosures should be e valuated. This is true for all wiring requirements: electrical power,

instrumentation data, communication data, and computer data, alarm signals, etc. A wiring system should provide

safe service and it should be maintenance free for many years after its initial installation. The wiring system should

not be the source of or a contributor to the electrical system outage problems. Electrical system outages in modern

industrial facilities may be very costly. For many continuous processes, an electrical power or control system outage

may present critical safety problems for the facility’s personnel and the people in the adjacent community.

In most cases, the wiring systems being considered are cable tray wiring systems or conduit wiring systems. When

cost evaluations are made between these two systems rarely is the cost of moisture in the conduit systems considered.

Wiring systems should be designed and installed so that they minimize the amount of condensed moisture or rain

water that they carry into the electrical equipment enclosures. For any wiring system, this requires some extra attention

to installation details.

Any above ground wiring system may be designed and installed so that it will not transmit significant amounts of

moisture into the electrical equipment enclosures. Cable tray wiring systems are more desirable than conduit wiring

systems where moisture is a problem. Conduit wiring systems require careful attention to many details to prevent the

moisture in the conduits from getting into the electrical equipment enclosures. Conduits breathe, they draw in moisture

laden air during the day and the moisture condenses when the temperature falls at night. This moisture builds up in

the conduit system and it drains into the electrical equipment enclosures. The moisture may cause the deterioration or

failure of electrical equipment. Electrical equipment failures may result in electrical system outages and excessive

maintenance costs. Seals (explosion proof) are sometimes installed in conduit systems as moisture barriers. Conduit

seals don’t prevent the movement of moisture or vapors at normal pressures in conduit systems. With atmospheric

pressure on both sides of the seal, moisture and vapors normally leak past the seal between the sealing compound and

the seal wall. It is also possible that moisture will leak along the conductor insulation surfaces past the seal.

There is no way to block moisture from a conduit system. The conduit system has to be designed with provisions to

harmlessly expel the moisture. This is done by engineering the conduit system details, something which is rarely done.

In some installations, the conduits need to be installed with controlled slopes for drainage. Breathers and drains must

be placed at critical positions in the conduit system. Drain holes may need to be drilled in some enclosures. Cable tray

wiring systems do not require the degree of details to cope with the moisture problems as do the conduit wiring

systems.

At an industrial facility was an outdoor installation. Vertical conduits contained the trip circuit conductors from the

vibration switches. Moisture from the conduits had totally immersed the vibration switches. At a minimum, a 1/4″

weep hole should have been drilled at the low point in the vibration switches cast iron boxes to get the moisture

supplied from the conduits out of the enclosures. This was not a total solution as the moisture from the conduits would

still keep the vibration switches in a high moisture environment. The conduit systems to the vibration switches needed

to be redesigned.





A good solution would have been to use a cable tray wiring system for the circuits associated with this compressor.

Multi conductor control cables could have entered the vibration switch cast iron enclosures via Cable trays Institute

Technical Bulletin 2 of 2 cable compression fittings. No moisture would flow into the enclosure from the wiring

system. The cable tray wiring system would have provided superior service. There would not have been any remedial

work to do.

Industry has found that the use of tray cables in cable trays results in wiring systems that require less maintenance

than had previously been required for an equivalent conduit wiring system. Tray cables in cable tray do not provide

significant moisture paths.

There are some good rules to follow when any type of wiring system enters outdoor equipment enclosures. Enter from

the bottom if possible. The next best choice is to enter from the side. A top entry is the last choice. Use a drip loop in

the cable with the bottom of the drip loop below the enclosure entry point. This will allow any rain water to have a

position where it will drop off the cable.

4- Cable Tray Type Selection

What type of cable tray should be used for the main runs of a cable tray wiring system?

The cable tray types to choose from are ladder, ventilated trough, or solid bottom. What are the reasons for selecting

a specific type of cable tray?

The engineer or designer should select the type of cable tray that has the features which best serve the project’s

requirements.

For a few types of installations, the National Electrical Code (NEC) specifies the cable tray type to be used:

Single conductor cables and Type MV cables must be installed in ladder or ventilated trough cable trays. Single

conductor cables and Type MV cables are not allowed to be installed in solid bottom cable trays [1993 NEC Section

318-3(b)]

In Class II, Division 2 Hazardous (Classified) Locations (Dust), the types of cables that are allowed to be installed in

cable trays must be in ladder or ventilated trough cable trays. Solid bottom cable trays are not allowed to be installed

in Class II, Division 2 locations [1993 NEC Section 02-(b)].

Ladder Cable Tray

Ladder cable tray is used for about 75 percent of the cable tray wiring system installations. It is the pre dominate cable

tray type due to its many desirable features:

A ladder cable tray without covers permits the maximum free flow of air across the cables. This allows the

heat produced in the cable’s conductors to effectively dissipate. Under such conditions, the conductor

insulation in the cables of a properly designed cable tray wiring system will not exceed its maximum

operating temperature. The cables will not prematurely age due to excessive operating temperatures.





The rungs of the ladder cable trays provide convenient anchors for tying down the cables in the non-

horizontal cable tray runs or where the positions of the cables must be maintained in the horizontal cable tray

runs. This capability is a must for single conductor cable installations. Under fault conditions (short circuit),

the magnetic forces produced by the fault current will force the single conductor cables from the cable tray

if they are not securely anchored to the cable tray.

Cables may exit or enter the ladder cable trays through the top or the bottom of the cable tray. Where the

cables enter or exit conduit, the conduit to cable tray clamps may be installed upright or inverted to terminate

conduits on the top or bottom of the cable tray side rail.

Moisture can’t accumulate in ladder cable trays.

If cable trays are being installed where working space is a problem, hand access through the cable tray bottom

may help to facilitate the installation of small diameter cables: control instrumentation, signal, etc.

The most common rung spacing’s for ladder cable tray is 30 cm. This spacing may be used to support all

sizes of cables. This spacing is desirable for the small diameter Type PLTC and TC cables as the support

distance is such that there is no visible drooping of the small cables between rungs. 35 or 40 cm rung spacing

provides adequate cable support but the slight amount of small diameter cable drooping between rungs may

be aesthetically objectionable for some installations. The maximum allowable distance between supports for

1/0 through 4/0 AWG single conductor cables is 9 inches [1993 NEC Section 318-3(b) (1)].

Ventilated Trough Cable Tray

The only reason to select a ventilated trough cable tray over a ladder type cable tray is aesthetics. No drooping of

small cables is visible. The ventilated trough cable tray does provide more support to the cables than does the ladder

cable tray but this additional support is not significant. It doesn’t have any impact on the cables service record or life.

Solid Bottom Cable Tray

The main reason for selecting solid bottom cable tray (with covers) is the concern of EMI/ RFI shielding protection

for very sensitive circuits. A solid bottom steel cable tray with steel covers provides a good degree of shielding if

there are no breaks or holes in the completed installation.

The solid bottom cable tray system has a disadvantage in that moisture can build up in the cable trays. This can be

controlled by drilling 1/4 inch drain holes in the bottom of the cable tray at three foot intervals (at the middle and very

near the sides) if the cable tray is not being used for EMI/RFI shielding.

Some engineers and designers specify solid bottom cable trays (often with covers) in the belief that all electrical

circuits have to be totally enclosed by metal. The cable trays are just supporting cables that are designed for such

installations. Cable failures in cable tray runs rarely happen. Cable failures due to cable support problems in cable

trays are nonexistent.





5- Tie Down Practices for Multi conductor Cables in Cable Trays (note

single conductor practices are to covered in a new bulletin)

There are three items which require decisions concerning the tying down of multi conductor cables in cable tray wiring

systems. Item #1 is to define under what conditions the multi conductor cables in cable trays are to be tied down. Item

#2 is to define the frequency at which the multi conductor cables are to be tied down. Item #3 is to select the ties that

have the proper characteristics for the specific installations. In the following material, where the word cable is used it

means multi conductor cable.

Item #1- Conditions Requiring Cable Tie Down:

The reasons for tying down cables are to keep them in the cable trays, to maintain the proper spacing between cables,

or to confine the cables to specific locations in the cable trays. National Electrical Code Section392.8 (B) states that

in other than horizontal cable tray runs, the cables shall be fastened securely to transverse members of the cable trays.

In horizontal cable tray runs, cables are not required to be tied down. The cable’s weight will keep them in the cable

trays. In non-horizontal cable tray runs, the cables must be tied down. For a vertical cable tray installation, the cables

may hang away from the cable tray if they are not tied down. The more flexible small diameter cables will hang

further away from the cable trays than the large diameter cables if they are not tied down. The smaller diameter cables

will need to be tied to the cable tray more frequently than the stiff large diameter cables.

Cable installations as per the 2005 NEC, sections 392.11(A) (3) and 392.13(A) 392.13(A) permit higher ampacities,

even the free air rating of the cable, where cables are installed in a single layer, in uncovered trays, with a maintained

spacing not less than one cable diameter between cables. Cable ties maintain this spacing and thereby permit hicher

ampacities.

There are installations where the owner may want the cables tied down to guarantee the separation of low energy

signal cables and power cables. This condition may also be obtained by installing a permanent barrier in the cable

tray. For installations where a single large cable or several cables are installed in ventilated channel cable trays, it is

at times desirable to tie the cables to the horizontal as well as to the non-horizontal ventilated channel cable trays.

Then if an abnormal condition occurs, the cables would not be knocked out of the ventilated channel cable trays which

are only 1 1/2 inches high.

Where Type MI cables are installed that are to have two hour fire resistant ratings, the MI cables must be securely

supported every three feet. A desirable installation would be to install the MI cable in steel cable trays and to use

stainless steel ties to secure the MI cable to the cable tray every three feet.

Where cables drop from the cable trays to equipment enclosures, it may be desirable to anchor the cables to the last

one, two or three rungs before the drop depending on the size of the cables. This easily provides distributed secured

support for the cables when the length of cable between the cable tray and the equipment enclosure is six feet or

longer.





Item #2 - Comments on Cable Tie Down Frequencies:

The NEC doesn’t specify any distances between ties for cables in cable tray wiring systems. This is a decision that

must be made by those designing and installing the cable tray wiring systems. It is desirable to develop some standards

for this activity.

A conservative recommendation for non-horizontal cable trays is that the small diameter cables (diameters less than

1 inch) be tied down at approximately 3 foot intervals and that cables 1 inch and larger be tied down at approximately

6 foot intervals.

The vertical cable wiring system installations that contain horizontal bends require the cables to be tied down at every

or every other rung in the bend and to the first rung before entering the bend and the first rung after exiting the bend.

In horizontal cable trays where cable spacing is to be maintained, the cables should be tied down at approximately 10

foot intervals. For horizontal ventilated channel cable trays, there are installations containing a single large cable or

several cables where it is desirable to tie down the cables at approximately 10 foot intervals.

Item #3 - Comments on the Types of Cable Ties:

Designers should select cable ties that have the proper characteristics for the specific installations. The initial

installation of the wrong cable ties may require maintenance expenditures to replace the cable ties. Plastic ties that

are not ultraviolet resistant will fail in one to two years if they are installed where they are exposed to the rays of the

sun. Where both indoor and outdoor cables are to be tied down on the same project, it is best to have only ultraviolet

resistant ties on the project and use them on both the indoor and the outdoor cables. This way it will not be possible

to have the incorrect type of ties for the outdoor cables.

When selecting cable ties the following must be considered: moisture resistance, ultraviolet resistance, extremely high

ambient temperatures, extremely low ambient temperatures, chemical resistance, flammability (UL 94 V-O

flammability rating), low smoke characteristics, tensile strength, appropriate lengths (the surplus lengths of the cable

ties are cut off so it is possible to use one tie length as standard where many different lengths are required).

There are quality plastic ties available that if properly applied have a life span of up to 20 years. There are non-

magnetic stainless steel ties as well as the plastic ties. The stainless steel ties are capable of satisfactorily satisfying a

wide range of requirements.

6 - Circuit Integrity of Cable Tray Wiring Systems during Natural Disasters

Earthquake and the hurricanes of past years emphasize that the design and installation of structures and systems that

may be subjected to these types of natural disasters should be such that the damage is kept to a minimum when a

disaster occurs. Even though having been damaged to some degree, it is important that the continuity of service for

critical systems be maintained until it is convenient and safe to shut the Systems down.





Figure #l is an Earthquake Seismic Zone Map of the Iran:

Figure #l





Figure #2 is Wind Velocity Map for the Iran:

Figure #2

It is extremely desirable that the circuit integrity of communication, instrumentation, lighting, power and safety

circuits be maintained when critical conditions exist. This is especially true for process and utility facilities where

there may be the potential for human safety problems, facility safety problems, adjacent facilities safety problems and

pollution problems.

To obtain high levels of continuous service, it is necessary that the electrical wiring systems specified have features

that will enhance the possibilities of the electrical circuit integrity being maintained under disaster conditions. The

wiring systems must be properly designed and installed using quality materials to obtain the desired results. There are

design and installation innovations that must be incorporated in the wiring systems.





Wiring System Selection Cable Tray Wiring Systems vs. Conduit Wiring Systems

Due to the materials that make up the systems, the circuit integrity of cable tray wiring systems will often excel that

of conduit wiring systems. During an earthquake of significant magnitude, long runs of conduit wiring systems are

very likely to be damaged to the extent that their insulated conductors lose their circuit integrity. An EMT conduit

system has a very high probability of tearing apart and damaging the conductor insulation producing circuit failures.

Rigid aluminum and steel conduits can fracture in the threaded areas at the couplings damaging the conductor

insulation producing circuit failures. If the conduits are being used as the equipment grounding conductors, unsafe

operating conditions result if the circuits continue operating with the equipment grounding conductor circuit open.

No similar relationships exist between the cable tray and the tray cable compared to that between the conduit and its

insulated conductors. The failure of the cable tray does not produce a conductor insulation failure in the cable which

results in the loss of circuit integrity.

A Design and Installation Philosophy

Above ground pipelines in some earthquake prone areas are designed so that if they leave their support systems they

will not fracture but will go safely to the ground. In these cases the pipelines are usually on supports that are just a

few feet off the ground. In the appropriate locations, this philosophy can also be applied to cable tray wiring systems.

The “fall to the Ground and Continue to Operate Feature” is much easier to obtain for cable tray wiring systems than

for pipelines. Cable Trays wiring systems can be designed and installed so that under severe earthquake conditions

the tray cables will fall to the ground with a very good probability that there will not be a loss of circuit integrity. This

may be important where the cable tray contains critical circuits related to the control and safety of pipelines, tank

farms, loading docks, facility utilities, critical industrial process, waste treatment plants, water preparation plants and

in some commercial facilities.

The design and installation philosophy described here may not be acceptable or desirable for many installations. For

those installations, Seismic Restrained Cable Tray Wiring Systems may be obtained by providing the proper

multidirectional bracing for the cable tray supports.

Some prudent design and installation decisions can be made to minimize the damage to cable tray wiring systems due

to earthquake or very high wind conditions. Use quality heavy duty cable tray such as a NEMA Class 20C designation

(Good for 100 pounds/foot where the distance between supports is 20 feet or less). Properly design and install the

cable tray runs. Use quality cables, the cable selection is very important. The cable’s construction, jacket material and

conductor insulation should be those that will best serve the requirements of the installation. This is not an area for

the cheapest cable that it is possible to obtain. For these installations, listed cables should be used. For circuit safety,

the individual cables should contain an equipment grounding conductor.





Design Features

In the event that a cable tray or the cable tray support system in a long cable tray run fails during an earthquake or

hurricane, surplus cable length (cable slack) in the cable tray will be a very important factor. The surplus cable length

will allow the cables to fall to a lower support level or all the way to the ground. The cable will have a high probability

of continuing to function. The height of the cable tray run above a potential support level for the cables is an important

factor. For the cable tray runs that are high above a support level for the cables, it may be desirable to make special

provisions to insure that there is surplus cable length in the cable tray. This is easily provided for the small diameter

cables that have small bending radii by increasing the width of the cable tray at certain increments in a cable tray run

(See Figure #3). The placement of these increased widths and their lengths would depend on the layout of the cable

tray system. One should be within 100 feet of the control room building or the motor control center building. If the

cable tray system goes down, there is enough surplus length in the cable near the buildings so that no excessive force

is exerted on the building wall or on the cable terminations. The other positions for surplus cable positions might be

required every 300 to 500 feet. Each long cable run should be analyzed to make sure that such installations are

absolutely required. This is not something that should be overdone. For installations that are just a few feet above the

ground and the cables have not been pulled so tight that some cable slack exists, special provisions to add cable length

are not usually required. The configuration of the cable tray system is important. A system of many bends will usually

have sufficient cable slack so that provisions for surplus cable length are not required. It is necessary that the designers

do a little “what if logical analysis” of the cable tray systems.

For the feeder and branch circuit power cables that have bending radii that can’t be accommodated in the configuration

as shown in Figure #3, there are other solutions. A wider cable tray may be used for the full cable tray run. The cables

can be installed in a gentle sine wave configuration over the length of the cable tray run. There are innovative ways

to obtain surplus cable length in the cable tray run for the large diameter cables by having an “S” loop in the large

cables as they drop from one cable tray to another at a different level.

Fig. 3 Installation practice to provide surplus cable length (cable slack) for small diameter cables in a cable tray run.

Installation shows ladder type cable trays with reducers between the different widths of cable tray. Bending radii of

the cable must not violate the cable manufacturer’s recommendations.





Cable Tray Wiring System Dependability is based on 30 Plus Years of Operating Experience

Why does the author feel that the proper type of tray cables used in cable tray wiring systems can maintain circuit

integrity in earthquake and hurricane situations? My many years of actual experience with cable tray wiring systems

have provided me some very good information. Cable trays and the tray cable can be subjected to sever abuse and

still safely perform their functions in a dependable manner.

Impact Tests

In the 1960s and early 1970s, many personnel in plants that were opposed to the Company Corporate Engineering

Department installing any cable tray wiring systems in their plants. the engineering departments worked with a few

plants to perfect cable tray wiring systems. main concern was cable damage due to mechanical impact. they did impact

tests on nonmetallic jacked cables equal to the Type TC and PLTC cables of today. When the temperatures of the

cables were a few degrees above freezing, had no problems when laid the cables on a concrete surface and hit them

with a steel hammer. When stored cable lengths in home deep freezers over and placed them on a concrete surface

and hit them with a steel hammer were getting jacket fractures on some of our specimens. . As several years of

excellent experience were obtained with very large scale cable tray wiring systems, the use of cable tray wiring system

became standard wiring system. In 30 plus years, we never had any cable damage due to mechanical impacts in the

ladder type cable trays without covers.

In 1973 members of the National Electrical Code’s Cable Tray Technical Committee had a two day meeting. This

was to work on the revision of Article 318- Cable Tray for the 1975 NEC. The members of the committee wanted to

study large industrial installations of cable tray wiring systems. A test set up was made of a cable tray section that

contained several types of multi conductor power and instrumentation tray cable. This set up was mounted on supports

three feet above the surface of the ground. Several members of the committee had the opportunity hit the cables in

the cable tray with 8 pound sledge hammers. After a number of hits, the cable tray was damaged but the damage to

the cables was cosmetic. Inspection showed that the electrical integrity of the insulated conductors in the cables was

not lost by the impact of the sledge hammers on the cables.

A real life industrial cable tray wiring system would not have its cables subjected to this degree of physical abuse.

The quality tray cables of today have much better impact resistant characteristics than those of the early 1970s. Tray

cables have the ability to take a great deal of abuse and keep on functioning without problems.

Hurricane Experience with Cable Tray Wiring Systems

I have been involved with many very large chemical and textile plant cable tray wiring systems (ladder type cable

tray without covers) located on the gulf coast that have been in operation for as long as thirty two years without circuit

failure problems. They have survived the effects of very high winds and have not suffered any damage.

The high winds that accompanied one hurricane gave us some evidence of the impact of strong winds on a cable tray

wiring system. In the late 1980s, several electrical engineers were in involved in the start up of a new chemical plant

unit at a coast site.





One of the feed stocks for this plant was Hydrogen Cyanide. The engineers had incorporated the most desirable

monitoring and safety systems in the plant design. During the start up period, a hurricane in the gulf produced some

80 mile per hour wind bursts at the plant site. One run of cable tray, in an exposed position 30 feet above the ground,

that contained a light weight cable load, had not been properly clamped properly to its supports. The cable tray went

down and some of the tray cables dropped to the ground. Some of the cables hung drooping from the support steel.

The control room and the motor control room wall cable transits were compression type so they had very strong grips

on the cable jackets. No force was transmitted to the conductor terminations as a result of the cable losing their support

or as a result of the wind action on the cables. Not a single instrumentation circuit, computer circuit, control circuit or

branch circuit lost its integrity.

All circuits continued to function. In due time the cable tray was replaced and properly clamped down. No electrical

circuit outages occurred during the storm after the wind storm or while the cable tray was being replaced. The cables

damaged were cosmetic.

None of the cables required replacement. This event showed that quality tray cables could withstand some harsh

conditions with no problems. These cables all contained their own equipment grounding conductor.

7 - Caution in Using Cable Tray Covers Outdoors

Improperly secured covers on outdoor cable trays can cause a serious safety hazard in high winds. In the majority of

cases, covers are not used on cable trays for technical or safety reasons, but due to the “raceway complex,” a feeling

by specifiers that cables must be totally enclosed in metal. Quality tray cables have a life of 30 to 40 years without

covers when exposed to the elements. For outdoor installations, the most desirable cable tray system is a ladder cable

tray or a ventilated trough cable tray without covers. If covers are used they should be the ventilated type.

Cable tray wiring systems have a 30-year plus proven track record of safety and dependability. They are the best

economic choice for commercial and industrial wiring systems.

Fig. 1. Wind Effect on Covered Cable Trays.





Strong winds moving across outdoor cable trays with solid covers create a negative pressure above the cable tray

cover and a positive pressure inside the cable tray. This is the same aerodynamic phenomenon produced on aircraft

wings to provide lift and maintenance of altitude. This pressure difference can lift covers off the cable tray if they are

not properly clamped to the cable tray with heavy duty clamps.

8 - Bonding Jumpers Not Required for Standard Cable Tray Splice Plates

It is not necessary to install bonding jumpers in parallel with the standard rigid aluminum or steel one-piece metallic

bolted side rail splice plates that are the connections between the cable tray sections. Here, the use of bonding jumpers

does not make a safety contribution to a properly installed cable tray system, and wastes both materials and labor.

For personnel and facility safety all the metallic electrical equipment enclosures and supports that may become

energized in the event of an electrical fault must be bonded electrically back to the equipment connection for the

system’s equipment grounding conductor cable tray wiring systems must comply with all the appropriate requirements

Of NEC Article 20 – Grounding Properly installed standard metallic splice plates provide the electrical continuity

between the cable tray sections to meet the NEC Section 31S6 (a) requirement that the electrical continuity of the

cable tray system shall be maintained.

During the 1970s, chemical industry engineers conducted fault current tests on the then designated NEMA Class II

aluminum and galvanized steel ladder cable tray components at the Bussmann Fuse – Sauget, Illinois Test Facility.

The setups consisted of four ladder cable tray sections to provide three different connections (C1, C2 & C3) between

the ladder cable tray sections that could be monitored during each test. The tests were confined to one side rail only,

which produced more severe conditions than it both side rails were allowed to conduct, current as is the case in an

actual installation.

Four bolt hole splice plates (2 bolts holes for each cable tray side rail) were used.

Test Current – 3,600 amperes for 14 cycles (Aluminum Cable Tray)

C1 Corroded Aluminum Rigid Splice Plate –

Connections between the splice plate and the side rails were one nylon bolt Splice plate temperature rise was 34

degrees Celsius.

C2 3/0 AWG Copper Bonding Jumper –

Connections between the copper bonding jumper and the side rails were AL-CU compression lugs with one steel bolt

Bonding jumper connection temperature rise was 75 degrees Celsius.

C3 Clean Aluminum Rigid Splice Plate –

Connections between the splice plate and the side rails was one steel bolt Splice plate temperature rise was 29 degrees

Celsius.





For this test, single nylon or steel bolts were used for each splice plate connection. In an actual installation, two steel

or stainless steel bolts would be used for the splice plate connection which would result in lower temperature rises in

the splice plates for the same fault conditions. The copper bonding jumper installation was the same as an actual

installation. The standard rigid splice plates tested had lower temperature rises than the copper bonding jumper

connection. The test performance of the splice plates was superior to the test performance of the copper bonding

connection.

No conducting compound was used between any of the contact surfaces. The normal oxide film on the aluminum was

not disturbed. No damage occurred on any of the test components. The test fault current flow time was excessive for

what would occur in an actual installation where the protective device ratings or settings were properly selected.

9 - Cable Tray Wiring Systems Have Many Cost Advantages

Cost is usually a major consideration in the selection of a wiring system. This article provides information as to where

cable tray wiring system cost savings will occur; however, it is not the intent of this article to state that the selection

of a wiring system should be based only on cost.

Early in the life of a project, the costs and the features of the applicable wiring methods should be evaluated to provide

decision information for the selection of the best possible wiring method or methods for the project. The evaluations

should include items that relate to cost, dependability, future changes, maintenance, safety, and space savings. Usually

the evaluation will determine if a cable tray wiring system or a conduit wiring system is to be selected as the projects

major wiring system. Both large scale and small cable tray wiring systems have been in use for the last 45 years in

parts of the world. Forty-five years of operating experience has proven that cable

Tray wiring systems are superior to conduit system wiring systems for power, control signal and instrumentation

circuits.

The following functions must be properly executed to obtain a quality wiring system installation:

1. Select the most desirable wiring method.

2. Properly design the wiring systems.

3. Specify quality materials.

4. Plan and execute the installation’s sequence of activities and the techniques to be used.

5. Control of the quality of the installation.

Depending on the type of circuits and the wiring density, an installed cable tray wiring system may result in a total

cost reduction (material + labor) of up to 60 percent compared to the cost of an equivalent conduit wiring system.

There is also the potential for cost savings to occur in the design, material procurement, installation and maintenance

areas when the wiring system is a cable tray wiring system.





Potential Design Cost Savings:

1. Very few projects are completely defined at the start of design. As a project progresses through the design phase,

the operating logic and safety requirements are developed and refined. The changes and additions required to

meet the projects needs occur all through the design cycle and at times even into the initial construction phase.

For projects that are not 100 percent defined before the start of design, the cost of and time used to cope with

changes during the engineering and drafting design phases will be substantially less for a cable tray wiring

system than for an equivalent conduit system.

2. It only takes a few minutes of design time to change the width of a cable tray to gain significant additional cable

fill capacity. For an additional cost of less than 10 percent of the basic cable tray cost, 6 inches of additional cable

tray width can be obtained. This extra 6 inches will accommodate large numbers of small diameter analog and/or

digital signal cables. Where banks of conduits are involved, any change in wiring capacity requirements during

the late stages of engineering and drafting design are very costly and time consuming. Significant conduit system

additions or revisions are usually required to provide exit and/or entry points in the conduit runs for the circuit

additions made late in the design phase.

3. Cable tray’s unique feature that allows a cable to enter or exit a cable tray anywhere along the cable tray’s

route provides for the easy accommodation of cable additions. No raceway wiring system has this unique

feature.

4. Using cable tray wiring systems simplifies the overall wiring system design process as fewer details are required

for properly designed cable tray runs than for properly designed conduit banks. Conduit system design can be

very complex due to the need for pull boxes, splice boxes and the involved conduit bank supports.

5. The fact that a cable tray system isn’t required to be mechanically continuous eliminates the need for many

complex installation details for conductor/cable entries into equipment and in dealing with cable tray run

interferences.

6. The installation space requirement is smaller for a cable tray than an equivalent capacity conduit system. For

cable tray systems, there is less apt to be space conflicts with other engineering disciplines on a project than for a

conduit system. Coordination design time is saved by dedicated fixed dimensioned installation zones for the cable

tray system. The cable tray installation zone’s size will not grow as changes are made as it does for conduit banks

in large projects.

7. Wire management systems for cable tray wiring systems consume less design time than is required for a conduit

system. A spread sheet based wire management program may be used to control the cable tray fill. While such a

system may also be used for controlling conduit fill, large numbers of individual conduits will require fill

monitoring while only a few cable tray runs require fill monitoring for an equivalent capacity wiring system.

3. Potential Material Procurement Costs Savings:

1. There are fewer different components in a cable tray wiring system than in a conduit wiring system. Fewer

different components means savings due to fewer components to specify, order, receive, store and distribute.

2. Excluding conductors, the cost of the cable trays, supports and miscellaneous items may provide a material

savings of up to 80 percent as compared to the cost of conduits, supports, junction boxes, pull boxes and





miscellaneous materials. The NEC fill capacity for an 18-inch wide ladder or ventilated trough cable tray is 21

square inches. It takes seven – 3 inch conduits to match that fill capacity.

3. For feeders or branch circuits, where the installations involve parallel phase conductors, there is a copper cost

savings for cable tray wiring systems. The derating factors don’t apply to three conductor or single conductor

cables in cable tray as they do for conduits. For the same circuit capacity of paralleled phase conductors, the cable

tray installation uses fewer pounds of copper than the conduit installation. Where phase conductors are not

paralleled, the cost of the 600 volt multi conductor cables used in cable trays is greater than the cost of the single

conductor cables used in conduit. This cost difference depends on the insulation systems, jacket materials and cable

construction.

4. Potential Installation Cost Savings:

1. The installation of a cable tray wiring system requires fewer man-hours than an equivalent conduit wiring system.

This is where the major cost savings are obtained for the cable tray wiring system. Smaller sized electrician

crews may be used to install a cable tray wiring system as compared to an equivalent conduit wiring system. This

allows for manpower leveling, the peak and the average crew size would be almost the same number. The

electrician experience level required for cable tray can be lower than that for a conduit wiring system as fewer

electrician with conduit bending skills are required.

2. Cable trays can be installed faster than conduit banks. Since the work is completed in a shorter time period there

is less work space conflict with the other construction disciplines. This is especially true if the installations are

elevated and significant amounts of piping are being installed on a project.

3. Many more individual components are required in a conduit system than in a cable tray system. This results

in the handling and the installing of large amounts of individual conduit items vs. small amounts of individual

cable tray items. At elevated installation levels, many additional man-hours will be required to transport the

components needed for the conduit system up to the installation level.

4. Conduit systems contain materials and installation practices that are more complex and costly to install than

those used in cable tray systems. This is the reason that cable tray installation labor costs are significantly below

conduit system installation labor costs. Conduit systems require pull or splice boxes where there is the equivalent

of more than 360 degrees of bends in a run. Cable tray systems don’t require pull or splice boxes. Conduit systems

normally require more supports and the supports are more complex. When penetrating walls, conduits banks

5. Require larger holes and more repair work than is required for cable trays. Concentric conduit bends for direction

changes in conduit banks are very labor intensive and costly.

6. However if they are not used, the installation will not be very attractive. The time required to make a concentric

bend is increased by a factor of three to six over that of a single shot conduit bend. This labor intensive practice is

eliminated when cable tray wiring system are used.

7. Conductor pulling is more complicated and labor intensive for conduit wiring systems than for cable tray

wiring systems. For conduit systems, it is necessary to pull from equipment enclosure to equipment enclosure.

The conduit system is required to be mechanically continuous from equipment enclosure to equipment enclosure.

Tray cables being installed in cable trays don’t have to be pulled through or into the equipment enclosures. Tray

cable may be pulled from near the initial enclosure along cable tray route to near the termination enclosure, then





the tray cable is inserted into the equipment enclosures for termination. Making the conduit system wire pulls

through the enclosures increased the possibility of conductor insulation damage.

5. Potential Maintenance Cost Savings:

1. An article in the October 1991, “Cable Pulling for Conduit Wiring Systems,” stated that 92 percent of the insulated

conductors that fail do so due to the fact that they were damaged during installation. The failures of the insulated

conductors may create unnecessary safety conditions and significant cost problems. Why not select a wiring

method where during the past 45 years its conductor failures due to installation damage have been almost

non-existent? Cable tray with quality cables is that wiring method. Conductor insulation failures in cable tray

wiring systems are rare. The reason for this that the tray cables are rarely damaged during the installation. Many

of the conduit conductors that fail do so due to the fact that they have been damaged when they were pulled into

the conduits. Excessive forces imposed on the conductor’s insulation system during the conductor installation

process can be very destructive. For some critical combinations of conductors and sizes of conduit, jamming of

the conductors in the conduit can occur during the conductor installation. This may result in conductor

insulation damage. Critical jam ratio (J.R. = Conduit ID/Conductor OD) values range from2.8 to 3.2. The 1996

NEC Chapter 9 Table 1. Fine Print Note is an alert for this serious problem.

2. If circuit additions are made in the future, the fact that the cables can enter or exit the cable tray anywhere

along its route allows for the cable additions at the lowest possible future cost. This is a feature that is unique

to cable tray. Future cable fill space capacity to accommodate cable additions to a cable tray can be provided at a

very low cost.

3. The cable tray wiring systems reduce the potential for moisture related equipment failures. Tray cables don’t

provide the internal moisture paths that conduits do. This lowers future maintenance costs. Moisture is a major

cause of electrical equipment and material failures. The day to night temperature cycling results in moisture laden

air being drawn into the conduits and the moisture in the air condensing. The condensed moisture accumulates

in conduits systems. The conduits pipe the accumulated moisture into the electrical equipment enclosures. Over

Time, thi moisture may accelerate the corrosion of some of the equipment’s metallic components and deteriorate

the equipment’s insulation systems to failure. Conduit seals are not effective in blocking the movement of moisture.

Conduit systems have to be specifically designed to reduce moisture problems and this is rarely done.

4. A properly designed and installed wiring system will not be a fire ignition source. It is possible that the wiring

system may be exposed to an external fire. For a localized fire, the damage to a cable tray wiring system will be

less to a cable tray system than to the conduit system. This has been the case in some industrial facility fires. The

damage to PVC jacketed tray cables and the cable tray is most often limited to the area of flame contact area

plus a few feet on either side of the flame contact area. When such a fire envelopes a steel conduit bank, the

steel conduit is a heat sink and the insulation of the conduit’s conductors will be damaged for a considerable

distance. Thermoplastic insulation may fuse to the steel conduit and the conduit will need to be replaced for many

feet. The rigid conduit had to be replaced for 90 feet. Under such conditions, the repair cost for fire damage would

normally be greater for a conduit wiring system than for a cable tray wiring system. In the Ohio chemical plant

fire, large banks of conduit and multiple runs of cable tray were involved. The cable tray wiring systems were

repaired in two round-the-clock days, and the conduit wiring systems were repaired in six round-the-clock days.

The conduit system repair required more than three times the manhours that was used for the cable tray system. In





the July 1995, “Protecting Life Safety Circuits In High Rise Buildings” the section titled “Protecting signal and

communication wiring” states the following: “Results of Steiner Tunnel testing performed by various cable

manufacturers actually indicates that conduits tend to act as heat sinks, thereby decreasing the time required to

damage insulation to cause conductor failures.” This is a big negative for conduit systems. Cable tray wiring

systems have significant cost savings advantages over conduit wiring systems. They also have convenience,

dependability and safety advantages over conduit wiring systems.

10 - Cable Tray Systems in Ducts, Plenums and Other Air Handling Space

The objective of this article to provide clear information as to the use of cable tray in those areas covered by Section

300-22 of the 1996 National Electrical Code.

Section 318-4 Uses Not Permitted states that “Cable tray systems shall not be used in environmental air spaces except

as permitted in Section 300-22 to support wiring methods recognized for use in such spaces. The wiring methods

allowed under Section 300-22 that utilize cable tray must follow the installation and safety requirements as covered

in Section 318 – Cable Tray.”

Many of the misinterpretations about cable tray are due to the fact that those misinterpretations are made with the

thought that cable tray is a raceway. It is not a raceway and it has never been a raceway in the National Electrical

Code. Cable tray is a mechanical support system just as strut is a mechanical support system. To install a metal support

system in an area rarely presents a fire safety problem. It is the cables that are being supported by the cable trays that

limit where a cable tray wiring system may be installed. The only limitation on the cable tray is that it can’t be used

in hoistways or where subject to severe physical damage. Any type of cable tray may be installed in the areas covered

by Sections 300-22(b), 300-22(c) and 300-22(d).

Installations for: Section 300-22(b). Ducts or Plenums for Environmental Air.

The section states that Type MI (Mineral Insulated) cable or Type MC (Metal Clad) cable employing an impervious

metal sheath without an overall non-metallic covering may be installed in Ducts or Plenums Used for Environmental

Air. For such installations, both of these cable types may be supported by cable tray.

Section 318-3(a) (1) states that Type MI cable may be installed in cable tray for support.

Section 330-12. Exception No. 2. States that “Type MI cable installed in cable trays shall comply with Section 318-

8(b).” Ladder or ventilated trough cable tray is an ideal support system for Type MI cable. Where small numbers of

Type MI cables are involved, ventilated channel cable tray is the ideal support system. Type MI cable is an excellent

cable for critical circuits. It has a UL two hour fire resistive rating when properly installed. It is safest wiring method

available.

Sections 318-3(a) (4) and 334-3(6) state that Type MC Cable may be installed in cable tray for support. Section 334-

10(b) states that “Type MC Cable installed in cable tray shall comply with Article 318.” Large amounts of the various

types of Type MC Cable have been installed in cable tray. The performance record has been excellent.





Installations for: Section 300-22(c) Other Spaces Used for Environmental Air.

The Cable Tray Institute’s Hot Line has received many requests for technical clarification assistance concerning

Section 300-22(c). There are two problems with the material relating to cable tray in this section.

1. The wording in the second paragraph “or solid bottom metal cable trays with solid metal covers” implies that the

types of insulated single conductors that are installed in raceways may also be installed in solid bottom cable trays

with solid metal covers. Due to the present wording of Section 300-22(c), there have been some installation made

that are not in compliance with Article 318. The cable tray was basically used as a wire way and in such cases the

rules of Article 362 (Wire ways) should apply. Depending on the specific installation, there may or may not be

safety problems with such installations but Section 318-3(b) doesn’t allow insulated single conductors to be

installed in solid bottom cable trays.

2. Single conductor installations in cable tray have the following limitations:

3. 1. The circuit conductors must be 1/0 AWG or larger [Section 318-3(b) (1)]. (b). They must be installed in ladder,

ventilated trough or ventilated channel cable tray [Section 318-3(b)].

4. 2. Such installations are limited to qualifying industrial establishments [Section 318-3(b)].

5. Some individuals have made erroneous interpretations of Section 300-22(c) concerning the types of cable tray that

may be installed in “Other Space Used for Environmental Air.” They assume that the wording of the second

paragraph means that only solid bottom metal cable tray with solid metal covers may be installed in these

installations. This is incorrect. Ladder, ventilated trough, ventilated channel or solid bottom cable tray may be

installed to support the applicable types of cables specifically listed for the use.

Allowable Wiring Methods that may be supported by Cable Tray for Section 300-22(c)

Installations.

Type MI cables, Type MC Cables without an overall non-metallic covering, Type AC cables and other factory-

assembled multi conductor control, power and signal cables that are specifically listed for the use. Some of the multi

conductor cables that are listed as plenum cables with adequate fire-resistance and low smoke producing

characteristics are Type PLTC Cables (Article725), Fire Protective Signaling Cables (Section 760), Optical Fiber

Cables (Article 770) and Communication and Multipurpose Cables (Article 800).

Installations for: Section 300-22(d). Data Processing systems.

The appropriate types of cables that are used for branch circuit conductors and data handling or signal cables may be

supported by cable tray under raised floors. The branch circuit cables in Section 645-5(d) (2) that may be supported

in cable trays are Type MI cable, Type MC Cable and Type AC Cable. Section 645-5(d) (5) and Section 645-5(d) (5)

Exception No. 3. List the various types of data and signal plenum cables with adequate fire-resistance and low smoke

producing that may be installed in data processing facilities. These cables can be installed in any cable tray type. Due





to the high wiring density, most raceway wiring methods are impractical for use in such installations while cable trays

have the features which make them ideal for modern wiring methods.

Wiring changes can be made easily where the wiring method is cables in cable trays. Cable trays are the way

to go for a state of the art wiring method that can easily accommodate changes at minimum cost in short time

schedules.

11 - Equipment Grounding Conductors for Cable Tray Systems

Cable tray wiring systems have excellent safety and dependability records. These excellent records are the result of

cable tray’s unique features plus the proper design and installation of the cable tray wiring systems. The intent of this

article is to review grounding practices for cable tray wiring systems. The Equipment Grounding Conductors are

the most important conductors in the electrical systems. The Equipment Grounding Conductor is the electrical

circuit’s safety conductor.

When designing a cable tray wiring system, the designer should evaluate the National Electrical Code’s (NEC)

Equipment Grounding Conductor (EGC) options that are applicable for the project.

Evaluate the following Options:

1. Use the cable tray as the EGC. [The cable tray may only be used as an EGC in qualifying facilities as stated in

NEC Section 318-3(c)].

2. Use a single conductor cable as the common EGC for all the circuits in the cable tray [NEC Section 318-3(b) (1)

Exception 2].

3. Use individual EGC conductors in each multi conductor cable in the cable tray (NEC Section 250-95).

4. Parallel the EGCs with the cable tray.

The requirements for the EGCs are covered in several Sections of the NEC.

NEC Section 110-10. Circuit Impedance and Other Characteristics. States that the components and characteristics

of a circuit must be properly selected and coordinated so that a fault (short circuit) will be cleared without extensive

damage to the electrical components of the circuit.

NEC Section 250-1(f). Fine Print Note (FPN) No. 2 states that conductive materials enclosing electrical conductors

or equipment are grounded to limit the voltage to ground on these conductive materials and bonded to facilitate the

operation of the over-current devices underground fault conditions.

NEC Section 250-51 states that the effective grounding path shall be: permanent and electrically continuous, have

the capacity to safely conduct any fault current imposed on it, have sufficiently low impedance to limit the voltage to

ground and to facilitate the operation of the protective devices.

NEC Section 318-6(a) states that cable tray is not required to be mechanically continuous but it must be electrically

continuous and bonding shall be in accordance with NEC Section 250-75.





It is desirable that a line to ground fault be quickly cleared by the circuit protective device. While the ground fault

exists, the facility personnel and also the facility may be exposed to unsafe conditions. Voltages may be distributed

through the facility’s metallic components in such a manner that they may produce conditions which can result in the

electrocution or injury of the facility personnel who physically contact the energized metallic components. There is

the potential for fire damage to the facility if the fault current electrical arcs become fire ignition sources.

A Look at the EGC Options Available for Cable Tray Systems.

1. Cable Trays as the EGCs.

NEC Section 318-3(c) Equipment Grounding Conductors states that metallic cable trays shall be permitted to be

used as EGCs where continuous maintenance and supervision ensures that qualified persons will service the installed

cable tray system and that the cable tray complies with the provisions of NEC Section 318-7 Grounding.

This means that cable tray may be used as the EGC in any qualifying facility. There is no restriction as to the type of

facility in which cable tray may be used as the EGC. The qualifying restriction is based on the expertise of the facilities

electrical maintenance staff. The involved electrical staff must be qualified.

Metal cable trays are Underwriters Laboratories (UL) Classified with regard to suitability for use as EGCs. The

Classification Marking states:” Classified by Underwriters Laboratories Inc. as to its Suitability as an Equipment

Grounding Conductor.” Cable tray is not listed by UL, it is classified by UL as an EGC.

The cross-section area of metal that is available for use as an EGC is shown in the Manufacturers catalogs for the

various cable trays. This is the sum of the cross section areas of the two side rails. For one piece construction cables

trays, the total cross section area is the sum of the side rail’s cross sections plus the solid bottom’s cross section area.

If the cable tray’s bottom contains ventilation openings, the ventilation openings reduces the cross section area of the

cable tray’s bottom available for EGC service. If the cable tray is to be used an EGC, it should be specified in the

purchase order and the manufacturer will mark or place a permanent information label on the cable tray’s side rail.

This marking or information label will specify the cable tray’s cross section EGC metal area and state that the cable

tray is UL Classified for Use as an EGC. It is not necessary to apply conductive compound on the standard cable tray

splice plate connections or to install bonding jumpers across the standard cable tray splice plate connections for

aluminum or steel cable tray.

Table 318-7(b) (2) “Metal Area Requirements for Cable Trays Used a Equipment Grounding Conductors”

shows the minimum cross section metal are that is required for aluminum or steel cable trays to be used as the EGC

based on the highest rating of any protective device (the fuse rating or circuit breaker tri setting) for the circuits in the

cable tray. If the cable trays cross section area is insufficient for the protective device rating, the cable tray can’t be

used as the EG and a separate EGC single conductor cable must be installed in the cable tray of each multi conductor

cable must contain an EGC conductor. Connections o conduits and/or cables (Bonding and/or EGC) to the cable trays





Should be mad with UL Listed Connectors that are properly installed to insure that there is goo electrical continuity

between the cable tray and the conduits and/or cables.

As per NEC Section 318-7(a), all metal cable trays must be grounded as required by NEC Article 250 regardless of

whether or not the cable tray is being used as an EGC.

2. Single Conductor EGC Cables in Cable Trays.

NEC Section 318-3(b) (1) Exception No. 2 states that insulated, covered or bare single conductors that are #4 AWG

or larger may be used as EGCs cables in cable trays.

When a single conductor EGC cable is used, the single conductor EGC cable must be sized for the fuse rating or

circuit breaker trip setting (NEC Table 250-95) of the highest capacity circuit in the cable tray that would potentially

utilize the single conductor EGC cable if a ground fault should occur.

In a moisture laden environment, a bare copper EGC should not be installed in an aluminum cable tray due to the

potential for electrolytic corrosion of the aluminum cable tray. For such installations, it is best to use a covered or

insulated conductor and to remove the covering or insulation where bonding connections are made to the cable tray,

bonding jumpers, raceways, equipment enclosures, etc. with UL Listed tin or zinc plated connectors.

While it is not a necessity, there are benefits to bonding the single conductor EGC cable to the cable tray run every

50 to 100 feet with a UL Listed connector. This puts the cable tray electrically in parallel with the EGC cable. If a

ground fault occurs, this practice can result in lower voltages to ground being impressed on fault energized metallic

Facility components. The electrically paralleled cable tray and the EGC cable become a low impedance EGC (See

Option #4). The EGC cables should be securely tied to cable tray every 10 to 20 feet so that under fault conditions,

the magnetic forces do not throw the EGC out of the cable tray.

5. Multi conductor Cables with EGCs in Cable Trays.

Multi conductor cables can be specified that contain their own EGC. EGC conductors in multi conductor cables may

be bare, covered or insulated. If covered or insulated, the outer finish must be green or green with one or more yellow

stripes [See NEC Section 250-57(b)]. In qualifying facilities, any insulated conductor in a multi conductor cable may

be permanently identified as an EGC by one of the three indicated methods indicated in NEC Section 250-57(b)

Exception No. 4.

The EGCs of Paralleled Multi conductor Cables in Cable Trays.

A significant change was made in NEC Section 250-95. Size of Equipment Grounding Conductors for the 1993

and 1996 NECs which impacts on the paralleling of standard multi conductor cables in cable trays. This change

requires an increase in the size of the EGCs in three conductor cables when the phase conductors are paralleled and

the EGCs are paralleled or a separate EGC of the proper size must be installed in the cable tray.





The proposals that were accepted to revise NEC Section 250-95 didn’t contain any documented safety problems. The

submitter’s substantiation was that conductors of cables are permitted to be paralleled so the single sized EGC as

applied to raceway systems should be applied to multi conductor cables. As a result “or cable” was placed after the

word “raceway” throughout NEC Section 250-95.

There haven’t been any public facts presented on any safety or technical problems due to operating standard three

conductor cables with standard sized EGCs in parallel. This has been a common industrial practice for several decades.

In many Chemical, Plastics and Textiles Manufacturing Facilities, the 480 volt feeders (Type TC Cables) from the

substations to the motor control centers have been paralleled standard three conductor cables with the standard sized

EGCs paralleled since the early 1960s.

For paralleled three conductor cables installed in cable tray to be in compliance with the 1996 NEC, one of the

following options must be selected:

A. Order special three conductor cables which contain larger sized EGCs. The size of the EGCs will depend on the

rating or setting of the circuit’s protective device as per NEC Table 250-95. This means that the size of the EGCs is

dependent on the number of three conductor cables that are paralleled to obtain the circuit capacity desired.

B. Use three conductor cables without EGCs and install a single conductor EGC in the cable tray or use the cable

tray as the EGC in qualifying installations as per Section 318-3(c).

C. Use standard three conductor cables with standard size EGCs and parallel the EGCs that are in the cable

assemblies with the single conductor EGC (Sized as per Table 250-95) in the cable tray or with the cable tray if it is

used as the EGC. This meets the NEC Section 250-95 requirements.





7. Electrically Paralleling the Single Conductor EGC and the Cable Tray.

Electrically paralleling the single conductor EGC with the Cable Tray by bonding the single conductor EGC to the

cable tray every 50 to 100 feet produces an installation that may provide some degree of improved electrical safety

for a facility and its personnel during ground fault conditions. The bonding of the cable tray run to the single conductor

EGC every 50 to 100 feet is not required by the NEC but it is a desirable optional practice.

A comparison is made below for an installation where the single conductor EGC isn’t electrically paralleled with the

cable tray and for an installation where the single conductor EGC is paralleled with the cable tray.

As a basis for a simple comparison of the two cases, the following assumptions are made:

System: One phase (277 volts) of the secondary of a 480 volt wye connected transformer is shown.

Conductors: The phase conductor is a 500 kg mil copper conductor with 75 degree C insulation. It is rated for 380

amperes with no de-rating for ambient temperature conditions. The protective device is rated at 400 amperes. The

EGC is a # 3 AWG copper (NEC Table 250-95). The cross section of the Aluminum cable tray side rails is 2 square

inches. The conductivity of the cable tray aluminum is about 55 percent that of copper.

Resistance of the 500 kg mil copper conductor is 0.0258 ohms/k FT.

Resistance of the #3 AWG copper conductor is 0.245 ohms/k FT.

Resistance of the aluminum cable tray is approximately 0.0143 ohms/k FT.

Resistance of the paralleled #3 EGC and the aluminum cable tray is 0.0135 ohms/k FT. [Resulting resistance of the

paralleled conductors is R1 x R2/R1 + R2. = (0.0143)(0.245)/0.0143) + (0.245) = 0.0135 ohms].

Assumptions: To simplify the examples, resistance values are used instead of impedance. In an actual installation,

impedance would determine the fault current magnitude and the voltage drops. The voltage drop across the arc of the

fault is omitted. It is assumed that all the return fault current will be confined to the single conductor EGC or the

single conductor EGC and the cable tray when they are electrically paralleled. It is assumed that the phase conductor,

the EGC and the aluminum cable tray are all the same lengths





Connecting the cable tray electrically in parallel with the single conductor EGC is an option worth considering. The

resulting reduced impedance of the EGC may provide for improvements in the facilities overall electrical safety. The

reduced impedance of the fault circuit will produce a higher fault current magnitude which will result in the protective

devices de-energizing the faulted circuit quicker. The shock potential to facilities personnel is lower (In the example

the 95 volts is still potentially deadly but it is not as apt to be fatal as is the 251 volts). The lower potential to ground

at the fault may result in lower magnitudes of stray fault current flowing through the facilities metallic items. This

reduces the chances of electrical arcs occurring which can be fire ignition sources.

12 - Grounding Inspection of Steel and Aluminum Cable Tray Systems

It is essential that the grounding of cable tray systems, including the cables in the tray systems, is inspected for

compliance with the grounding requirements in the National Electrical Code (NEC) BEFORE the cabling in the tray

is energized and BEFORE cable is installed. If cable is installed, then it is possible to energize the cable before a

grounding inspection. It is also easier to do the cabletray grounding inspection if the tray system does not have cable

installed. Electrical grounding is essential for personal safety and protection against arcing that can occur in any part

of the wiring system, motor enclosures, conduits, etc. The owner, engineering firm, or their designated representatives

should provide approval of the inspection.

For safety reasons, the grounding should be right before the wire is energized. This is true for cable tray, conduit,

cable, or any electrical system. The grounding inspection should start with the installation and should continue until

all tray sections are connected together, either by bolted connections or bonding jumpers.

Steel and aluminum cable tray systems are excellent equipment grounding conductors if they are properly designed,

specified, installed, and inspected. The NEC requirements for cable tray grounding are found in NEC Sections 318-

3c, 318-7, and Table 318- 7(b) (2).





For the cable tray to be used as an equipment grounding conductor, the tray must be used where continuous

maintenance and supervision ensure that qualified persons will service the installed cable tray system and that cable

tray section must be:

1. Marked as “Classified by U.L. as to its suitability as an Equipment Grounding Conductor.”

2. Marked with the minimum cross sectional area of the tray.

Grounding inspection consists of verifying that all cable tray sections are marked as indicated

above.

This can easily be accomplished as each part of the tray system is installed. If the cable tray system is not specified

or marked as an equipment grounding conductors then either a single conductor equipment ground conductor must

be installed in the tray or equipment ground conductors must be provided in the cables installed in the tray system.

The equipment ground conductor is so important that some companies use ground conductors in the cable and the

cable tray as an EGC. Many companies are moving towards ground conductors in the cable for added reliability.

A single conductor ground conductor can be installed in and bonded to the cable tray sections. NEC section 318-

3(b)(1), exception number 2 permits single conductor cables in sizes #4 AWG or larger either insulated, covered, or

bare as equipment grounding conductors. The minimum size is based on NEC Table 250-95 based on the highest fuse

rating or circuit breaker setting for any circuit in the tray system.

In a moisture laden environment where aluminum tray is used a bare copper conductor should not be used to avoid

galvanic corrosion; an aluminum conductor should be used with the proper listed connectors to bond tray sections

together.

Equipment ground conductors in TC cables are sized to meet NEC Table 250-95. In cables #8 gauge copper or larger,

they are separate conductors either bare or insulated. In cables #10 gauge copper, a fourth conductor, the same size as

the phase conductor, can be used or marked as an equipment ground conductor in industrial facilities.

Grounding inspection should verify that the cable tray is marked as an equipment grounding

conductor, this is always preferred, or a single conductor equipment ground conductor is

installed and bonded to the cable tray sections, or equipment ground conductors are provided

in the cables.

Regardless of which type of equipment grounding system used, cable tray systems must be electrically continuous

and effectively bonded and grounded per Section 250- 75 in the NEC.

The most important bonding jumper is the connection from the tray system to the power source at the MCC or

switchgear. It is good practice to provide bonding jumpers from both side rails of cable tray section at the MCC or

switchgear to the ground bus in the equipment. Verify that these bonding jumpers are provided. Bonding can also be

accomplished by direct bolted connections to cable tray sections.





Bonding jumpers are not required across standard splice plates because bolted connections provide adequate

bonding. Bonding jumpers are required at adjustable splice plates, expansion splice plates, or at discontinuous tray

sections.

Cable dropouts from the tray system to various types of enclosures must provide bonding to the tray system either by

bolted connections to channel dropouts (use at least two bolts), grounding conductors in the cable or bonding jumpers

for cable dropouts, or conduit-to-cable tray adapters as indicted in figures 4.48 through 4.5 for NEMA VE-2. Note: if

adapters are not listed for grounding, bonding jumpers are required.

13 - Hot-Dip Galvanized vs. Aluminum

One of the most important choices when designing a cable tray system for corrosive or outdoor environments is the

material. Steel cable tray with a Hot-Dip Galvanized after Fabrication (ASTM A123) finish has been used successfully

for many years. Increasingly, however, aluminum is becoming the material of choice for cable tray systems. In these

days of shrinking construction budgets, why would engineers, contractors, and end users choose aluminum cable tray,

which typically has a slightly higher initial cost, over Hot-Dip galvanized steel cable tray? The answer lies in

aluminum’s many advantages in design, installation, delivery, performance and total cost over the lifetime of the

installation.

Design and Installation

Most people know of aluminum’s superior strength-to-weight ratio. For example, a 36″ wide, 24-foot section of ladder

cable tray with a 6″ side rail, NEMA 20C hot-dip galvanized steel cable tray weighs about 200 lbs, whereas the same

cable tray in aluminum weighs only about 100 lbs. When installers must carry and put cable tray sections into place,

which may be 30′ or more above ground, aluminum’s lighter weight can mean the difference between needing just

two installers instead of four.

Field cuts are also much easier with aluminum cable trays, not only because aluminum is easier to cut, punch, and

drill, but there is no need to apply a protective coating to the exposed edges. The hot-dip galvanized coating on steel

must be repaired with a zinc rich paint (also called cold galvanizing) which is inferior to the original galvanizing,

leaving a chink in the steel’s armor against corrosion. Of course, there is always the chance that some contractors may

not repair the cuts at all, further impairing the cable tray’s corrosion resistance.

Because aluminum cable tray components are extruded, material can be used more efficiently and tolerances remain

tighter. Some manufacturers have used this to the contractor’s advantage by creating splice joints and other features

which offer better performance and require less labor to install. And when using cable tray as an equipment grounding

conductor (EGC), aluminum’s superior current carrying capacity reduces the need to purchase and install a separate

EGC (in qualifying industrial installations) and also increases the safety of the installation by providing a better fault

current path.





Delivery and Availability

Aluminum cable tray systems can normally be shipped from the factory in a short period of time. Small orders can

ship in just a few days, depending on the manufacturer’s work-load. Hot-dip galvanized cable tray systems typically

take several days to fabricate, hot-dip galvanize, and prepare for final shipment.

All cable tray manufacturers must ship their cable trays to a third party to have them galvanized. This requires that

the cable tray be manufactured, packed and shipped to the galvanizer. Some manufacturers return the material to their

plants after galvanizing to inspect and deburr the product prior to packing and final shipment. Other manufacturers

rely on the hot-dip galvanizer to inspect, deburr, and pack the material for shipment. The cost of a delay in getting

material to the jobsite is many times the cost of the material itself and using aluminum cable tray helps to minimize

the chance of delays.

Hot-dip galvanized steel cable tray covers pose another problem. Placing thin gauge steel covers in a hot zinc bath

will often cause the covers to warp. To avoid this problem, thicker material is used and the covers are limited to six

feet long. The extra material and the extra labor required to install shorter covers has a significant impact on the cost

of the entire cable tray system.

Performance

Aluminum cable tray has excellent corrosion resistance in many chemical environments and has been used for over

thirty years in petro-chemical plants and paper mills along. The aluminum alloy used is 6063-T6, which is considered

copper-free and sometimes referred to as marine grade aluminum. Although copper-free aluminum may experience

some chloride pitting in a marine environment, this corrosion is limited and does not affect the structural integrity of

the system.

Galvanizing on steel cable trays is designed to slowly wear away as it protects the steel; any place where the coating

is thin or has been removed can prematurely limit the product’s service life. Since aluminum cable trays are

homogenous material throughout, their service life is unaffected by scratches and field modifications. When

aluminum cable trays are used with stainless steel hardware, the system can perform indefinitely, with little or no

degradation over time, making it ideal for many chemical and marine environments.

Total Cost

Aluminum’s many advantageous features like its corrosion resistance, superior strengthto-weight ratio, ease of field

modification, fast delivery and availability, and labor saving installation all add up to a system well worth the extra

10% to 15% in initial price. Recently, the relative cost of aluminum to steel has been decreasing, making the choice

between aluminum and steel no contest.





14 - Cable Tray Width Selection for Installations with 600 Volt Single

Conductor Cables

National Electrical Code (NEC) Section 318-11 Ampacities of Cables, Rated 2000 Volts or Less, in Cable Trays.

(b) Single Conductor Cables allows cables of identical construction and conductor material to be operated at different

maximum ampacities depending on the physical placement of the cables in ladder or ventilated trough cable trays.

NEC Section 318-10 Number of Single Conductor Cables, Rated 2000 Volt or Less, in Cable Trays. (a) Ladder

or Ventilated Trough Cable Trays. Doesn’t cover the width requirements of ladder or ventilated trough cable tray

for all the types of installations that contain single conductor cables.

This is best exhibited by cable tray width calculations for three different examples of single conductor cables in ladder

or ventilated trough cable tray that are permitted by NEC Article 318. The examples are based on installations that

contain 12 – 500 kg mil cables (four – three phase – 480 volt circuits or a circuit of four paralleled conductors per

phase). The 500 kg mil copper single conductor cables have 600 volt 75 degree centigrade insulation. The cable’s

diameter equals 1.07 inches and the cable’s area equals 0.90 square inches.

Example #1 is based on the requirements in Sections 318-10(a)(2) and Section 318-11(b)(2).

Section 318-10(a)(2) states that the sum of the cross-sectional areas of the single conductor cables shall not exceed

the allowable fill area in Column 1 of Table 318-10 for the appropriate ladder or ventilated trough cable tray width.

12 cables x 0.90 square inches /cable = 10.8 Square Inches

Table 318-10 – Column 1 shows that the minimum cable tray width that has adequate fill area is a 12 inch wide cable

tray. The 12 inch wide cable tray has an allowable fill capacity of 13.0 square inches which slightly exceeds the

installation’s 10.8 square inch requirement.

Section 318-10 states that the single conductors or conductor assemblies shall be evenly distributed across the cable

tray. This statement leaves the exact cable arrangement in

the cable tray up to the designer. Following are two

examples of installations that meet the intent of Section

318-10. The cable installation shown in Figure 1A is

technically superior to that shown in Figure 1B.

The installation of the cables in the cable tray as per

Figure 1A is very desirable as the cables are in an

arrangement where they are equilaterally spaced. This

will result in equal reactances for the circuit’s phase

conductors. If each of the phase conductors





has the same resistance and reactance, the currents to and the phase voltages at the utilization equipment will be

balanced assuming that all the loads are balanced three phase loads. Motors that are supplied with unbalanced three

phase voltages experience additional heating due to the voltage unbalance. A few percent voltage unbalance can be

very detrimental to the length of the motor’s operating life.

For the Figure 1A and Figure 1B cable installations, Section 318-11(b)(2) states that the maximum ampacities of the

cables in ladder or ventilated trough cable trays without covers is 65 percent of the values in Table 310-17

For the Figure 1A and Figure 1B installations, the allowable maximum operating ampacities (Table 310-17) for the

500kcmil conductors is 620 Amperes x 0.65 = 403 amperes per conductor (without the use of a maximum ambient

operating temperature correction factor).

Example #2 is based on the requirements in Section 318-11(b)(3).

Section 318-11(b)(3)states that where single conductors are installed in a single layer in uncovered cable trays, with

a maintained space of not less than one cable diameter between individual conductors, the ampacities of Nos. 1/0 and

larger cables shall not exceed the allowable ampacities in Table 310-17.

Section 318-11(b)(3) defines the arrangement of the cables in the cable tray to obtain the conditions that allow the

cables to carry the higher ampacities. Section 318-11(b)(3) contains permissible ampacity information and it also

contains information that impacts on the cable tray width selection.

If the width of the ladder or ventilated trough cable tray is selected based on the requirements of Section 318-10 for a

installation being made as per Section 318- 11(b)(3), the cable tray will be of insufficient width for the intended

installation.

To determine the required width of a ladder or a ventilated trough cable tray as per Section 318-11(b)(3).

Total width of the Cables — 12 x 1.07 inches = 12.84 inches

Space between cables must be equal to one cable diameter — 11 x 1.07 inches = 11.77 inches.

Total cable tray width required is 12.84 inches + 11.77 inches = 24.61 inches. A 30 inch wide cable tray must be used.

For Figure 2 installations, the allowable maximum operating ampacities (Table 310-17) for the 500kcmil conductors:

is 620 Amperes per conductor (without the use of an maximum ambient operating temperature correction factor).





This cable arrangement will result in some unbalance in the phase currents and voltages due to the fact that the cables

are not equilaterally spaced. The distances from the conductor centerlines of the Phase A to Phase B and from the

Phase B to the Phase C are equal but the distance between centerlines of the Phase C conductor to the Phase a

conductor is larger. The reactances for the three phases will not be equal which will result in the currents to and the

phase voltages at the utilization equipment being unbalanced. If the circuits are of a length where it is possible to

transpose the phase conductors, the reactances of the phase conductors can be equalized. Two transposition would

allow each phase conductor to occupy each of the three conductor positions for 1/3 of the length of the run. For very

long runs, it may be desirable to have many transpositions but regardless of the number of transpositions each phase

conductor must occupy each of the three conductor positions for 1/3 of the length of the run.

This type of installation can only be made where the cables can be terminated without entering raceways (The

ampacities in Table 310-16 must be used if the cables enter a raceway). Examples would be at a transformer secondary

or at a bus extension from switchgear.

It is best to use the 75 degree C ampacity values even if a 90 degree C insulated cable is installed unless it is known

that the equipment can accommodate the termination of the higher temperature conductors. For the Figure 2

installation, the 90 C insulated conductor operating at its maximum ampacity will produce 27 percent more heat than

will the 75 C insulated conductor. See NEC Section 110-14(c).Temperature Limitation.

Example #3 is based on the requirements in Section 318-11(b) (4).

Section 318-11(b)(4) states that where single conductors are installed in a triangular or square configuration in

uncovered cable trays, with a maintained space of not less than 2.15 times one cable diameter between the cable

groups, the ampacities of Nos. 1/0 and larger cables shall not exceed the allowable ampacities in Table B-310-2 in

Appendix B of the NEC.

Section 318-11(b)(4) defines the arrangement of the cables in the cable tray to obtain the conditions that allow the

cables to carry the higher ampacities. So Section 318- 11(b) (4) contains permissible ampacity information and it also

contains information that impacts on the cable tray width selection.

If the width of the ladder or ventilated trough cable tray is selected based on the requirements of Section 318-10 for a

installation being made as per Section 318- 11(b)(4), the cable tray will be of insufficient width for the intended

installation. To determine the required width of a ladder or ventilated trough cable tray as per Section 318-11(b)(4).

Total width of the Cables — 8 x 1.07 inches = 8.56 inches

Space between cables must be equal to 2.15 times one cable diameter — 3 x 2.15 x 1.07 inches = 6.90 inches. Total

cable tray width required is 8.56 inches + 6.90 inches = 15.46 inches.

An 18 inch wide cable tray must be used.





For Figure 3 installations, the allowable maximum operating ampacities (Table B-310-2) for the 500kcmil conductors

is 496 amperes per conductor (without the use of a maximum ambient operating temperature correction factor).

The installation of the cables in the cable tray as per Figure 3 is very desirable for the reasons stated concerning Figure

1A.

This type of installation can only be made where the cables can be terminated without entering raceways. The

ampacities in Table 310-16 must be used if the cables enter a raceway.

It is best to use the 75 degree C ampacity values even if a 90 degree C insulated cable is installed unless it is known

that the equipment can accommodate the termination of the higher temperature conductors. For the Figure 3

installation, the 90 C insulated conductor operating at its maximum ampacity will produce 37 percent more heat than

will the 75 C insulated conductor. See NEC Section 110-14(c). Temperature Limitation.

When utilizing cable tray to support cables, the designer has cable installation arrangement options available which

allow the same size cables to operate at different ampacities if the appropriate cable tray width is selected.

The maximum allowable ampacity for the 500 kg mil cables installed as per Figures 1A and 1B is 403 amperes – (12

inch wide cable tray).

The maximum allowable ampacity for the 500 kg mil cables installed as per Figure 2 is 620 amperes – (30 inch wide

cable tray).

The maximum allowable ampacity for the 500 kg mil cables installed as per Figure 3 is 496 amperes – (18 inch wide

cable tray).

15 - Cable Tray Grounding: Power, Instrumentation, and

Telecommunications

Grounding has always been a controversial topic. But, with the growth of digital high frequency systems the issues

are more complex. Grounding means connected to earth or a conducting body that acts in place of earth. Some

international standards refer to grounding as earthing. Bonding is the interconnection of metal parts to establish

electrical continuity. These definitions are NEC terminology and apply to power system grounding.





The purpose of grounding is:

Fire Protection

Electrical Shock Protection

Electrical system ground fault protection

Lighting protection-building and electrical system

Electrical Noise and EMI protection

Voltage Stabilization

Power System Grounding

Power circuit grounding of cable trays is explained in CTI Technical Bulletins, Titles No. 8, 11, and 12, and the

National Electrical Code Sections 318-3-© and 318-7. It is also covered in NEMA Standard VE-2.

The purpose of power grounding (Article 250) is to minimize the damage from wiring or equipment ground fault.

Cable tray systems are in the path of ground fault currents. Cable tray systems are bonded together through their

bolting, connectors splice plates, clamps, and bonding jumpers where there are gaps in the cable tray system. Cable

tray systems are not required to be mechanically continuous, but shall be electrically continuous. Cable trays are also

bonded to conduit, cable channel or other wiring drops. They must also be bonded back to the power source. All

bonding jumpers must be sized (as a minimum) to meet the requirements of equipment grounding conductors. Both

side rails of the tray must be bonded together to the next section. Cable trays can be used as the only equipment

grounding conductor (EGC), but they must meet certain criteria (only in qualifying facilities, minimum cross-sectional

areas, U.L. classified as to suitability, etc., see NEC 318-7).

There are other alternatives-use EGC’s in the cable (U.L. listed cable can be supplied with EGC’s in certain conductor

sizes) or a separate EGC in the cable tray that bonds the cable tray sections together and can also be used to tap EGC’s

to individual drop-outs from the CT. These two alternatives can be used for non-metallic cable trays. Cables with

equipment ground conductors within the cable are an accepted practice in industry. They provide a two-point

connection from the power source to the load, however, any conduit, cable tray, or raceway must still be bonded back

to the power source.

Some companies do not accept conduit as an EGC.

The EGC system is a critical safety system. Therefore, it is prudent to treat the cable tray system as an equipment

grounding conductor in parallel with the ground conductors in the cables or an individual ground conductor.

Cable Tray Grounding-Signal and Communication Circuits

Where cable tray systems contain only signal and communication circuits that operate at low energy levels, power

grounding per NEC Section 318-7 is not appropriate, but cable tray grounding for lightning protection, noise, and

electromagnetic interference is necessary.





For telecommunications circuits TIA/EIA standard 607, Commercial Building Grounding and Bonding Requirements

for Telecommunications, provides grounding for these systems. Voltage disturbances, lightning induced voltages, and

radiated EMI are the concern. Lightning protection is a concern if cable trays are located on the top of buildings, in

an outdoor exposed area, or in the path of lightning currents. An overhead cable system can provide protection.

NFPA780, Standard for the Installation of Lightning Protection Systems 1997 Edition, provides the criteria for

building lightning protection.

Cable tray designs are also available that are EMI/RFI shielded. The tray is totally enclosed and the gaskets and covers

are constructed and tested to meet EMI standards for the protection of the sensitive circuits in the cable tray against

external electric and magnetic fields. Solid bottom cable trays also provide some degree shielding as do cable tray

covers. Steel provides effective shielding at frequencies up to approximately 100 kilohertz however at higher

frequencies, in the megahertz range, aluminum or copper shielding is more effective.

Cross Talk

Cable tray systems that contain signal and communication circuits should be grounded and, in some situations,

shielded from external electrical and magnetic disturbances. In addition to these concepts, the CTI has received a

number of questions concerning the coupling of electrical noise from power wiring into sensitive circuits because the

wiring is within the same cable tray or close to the cable tray. The key question is how far apart the power does and

Signal cables have to be. The most desirable design is to separate power and signal cables in separate cable trays, or

to separate wiring systems by a barrier.

The sensitivity of signal systems depends on a number of complex factors. Including electronic circuitry involved,

isolation or coupling to ground, filtering, the signal type and logic, type of signal cable (untwisted pair, twisted pair,

shielded twisted pair, and coaxial cable double-shielded coaxial cable) and characteristic impedance of the circuit and

cable. Some systems are quite tolerant to external noise. For instance, 4 to 20MA instrument signal systems and

telecommunication circuits do quite well with respect to noise.

Some companies and organizations have published their own recommended practices and they should be followed.

The national standard that includes separation distances is the Institute of Electrical Electronic Engineers (IEEE)

Standard 518, IEEE Guide for the Installation of Electronic Equipment to Minimize Electrical Noise Inputs to External

Sources. The cable spacing criteria found in this standard is large, based on industry experience. Many systems work

quite well with lesser distances. Much depends on the particular installation. Typical spacing of cables in trays used

in various industry standards varies from two inches to four feet. In some situations, two inches is probably adequate.

AC Drives

There have been a number of noise problems (and other problems) with the application of the newer IGBT AC Pulse

Width Modulated Adjustable Speed Motor Drives. The new IGBT Drives produce fact rise time pulses that produce





high voltage, high frequency pulses in the power wiring from the Inverter electronics to the motor. (The IGBT is a

new type of power semiconductor.) This power wiring is essentially a radiator of high frequency power.

The noise frequency can be as high as 30MHZ. A number of IEEE papers have been presented on this topic. In

particular, they provide detailed studies analysis and noise measurements using different types of motor power cable

types. The conclusion is that one can manage this concern by proper grounding and power cable selection. At these

frequencies, based on tests, the power cable should be shielded with a metal armor or foil either copper or aluminum.

These studies and technical papers indicate that:

1. Shielded cable-either type TC or MC should be used

2. Nonferrous metal, such as aluminum, becomes the metal of choice at high frequencies for the cable shield

3. Additional high frequency bonding is required

Conclusion

Cable tray systems have been used extensively to support sensitive electronic circuitry. For many circuits shielding

and separation requirements are minimal. Proper attention to the following can manage noise and EMI concerns:

Signal cable

Grounding of signal circuits and cable shields

Cable selection

Cable tray grounding

16 - Types of Cable Typically Used in Cable Tray

The purpose of a cable tray system is to support, route, and protect cable as part of the cable management system.

Through NEMA and the Cable Tray Institute numerous articles, standards, and other general guidance can be found

regarding the proper use and installation of cable tray systems.

The cable tray system is only one component of the cable management system. Another important component is

obviously the cable. Therefore, it is also important to understand how to properly apply and install the cables in a

cable tray system. To that end this Bulletin is intended to discuss the types of cables most frequently used in cable

trays and the wiring methods permitted in cable trays under the National Electric Code (NEC) NFPA 70.

In general, tray rated cables are quality products that have been tested to withstand the rigors of severe environments.

They are protected by either a plastic Jacket or metal armor over individual conductor insulations. They can be rated

for outdoor, indoor, for corrosive areas, for hazardous locations, or high electrical noise areas. They should be UL

listed indicating they have been tested for ratings relative to flammability resistance, mechanical resistance and

temperature limitations. Many cable tray rated cables include a crush and impact test as part of the listing and are

rated as exposure rated (ER). ER cable is allowed to leave the cable tray for distances up to six feet, as long as it is

supported and secured.





In many cases there is more than one type of cable for a particular application, for instance both cables rated as tray

cable (TC) and cables rated as metal clad (MC) can be used for 600- volt motor power cables. In all instances cables

utilized within a cable tray system should be UL listed and marked as cable tray rated.

The types of cables, allowed in cable trays, and the wiring methods permitted in cable trays can be found in NEC

Section 392.10 (A). This Section also lists various corresponding NEC Articles which describes the conditions of use,

and installation requirements for a particular class or type of cable. Additional considerations such as fill capacity,

allowable ampacity, cable splicing within trays, and securing and supporting cables are addressed in Article 392.

Users should be familiar with all these Articles, and check the manufacturer’s specifications, to verify selected cables

meet all application requirements and NEC requirements.

The most frequently used tray cables are:

1. Tray Cable – type TC

2. Power Limited Tray Cable – type PLTC

3. Instrumentation Tray Cable – type ITC

4. Metal Clad Cables – type MC

5. Mineral Insulated, Metal Sheathed Cables – type MI

6. Optical Fiber Cables – types OFC thru OFN

7. Communication Cables – types CMP, CMR, CMG, CM, CMX

8. Fire Alarm Cables – type NPLF – NPLFP, FPL-FPLP (CI)

Type TC – Tray Cable – (NEC Article 336) –Power and control tray cable type TC is a factory assembly of two or

more insulated conductors, with or without associated bare or covered grounding conductors, under a non-metallic

jacket. TC cables are rated for 600 volts and can be used in industrial power or control circuits, where flame retardant

cables are desired.

Allowed installations include cable trays, raceways, and outdoor locations where supported by a messenger wire.

Type TC cable is UL listed for use in Class 1, Division 2 hazardous locations, and Class 1 control circuits. If identified

for such use TC cables may be also be used for direct burial.

In industrial establishments where conditions of maintenance and supervision ensure that only qualified persons will

service the installation, the cable is continuously supported, and is protected against physical damage, type TC tray

cable that complies with crush and impact requirements (type TC-ER cables) are permitted between a cable tray and

the utilization equipment or device. The cable must be secured at intervals not exceeding six feet.

TC cables are not permitted to be installed outside of a cable tray system or raceway with only two exceptions (1) in

outdoor locations supported by a messenger wire. (2) Where not subject to physical damage, Type TC-ER cable is

permitted to transition freely between cable trays and between cable trays and equipment for distances up to six feet

without continuous support.





Type PLTC – Power Limiting Tray Cable – (NEC Article 725)

Type ITC – Instrumentation Tray Cable – (NEC Article 727) – These types of cables are instrumentation cables

and are available in shielded or unshielded constructions consisting of multiple single conductors, unshielded or

shielded twisted pairs, with or without a metal armor. They have a 300 volt insulation rating and are available in sizes

22 AWG to 12 AWG. PLTC cables are intended for non-plenum and non-riser Class 3 and Class 2 circuits. They are

specially designed for use with power limiting circuits. Application of PLTC cables requires the power supply listing

requirements of Article 725.

To avoid this complication an alternative class of cable, Instrumentation Tray Cable (ITC) cable, was added to NFPA

70 – 1996. ITC cable is described in Article 727 and does not have the power supply limitations of Article 725.

However, ITC cable may only be installed in instrumentation and control circuits operating at 150 volts or less and 5

amperes or less.

Today many manufacturers dual rate these cables as PLTC / ITC. Cables of either class or the dual rated cables are

also available with an ER rating and as such may be installed as previously discussed under TC- ER cables with the

exception that PLTC-ER and ITC-ER must be continuously supported using mechanical protection such as struts,

angles, or channels and secured every six feet.

ITC cables may be installed in industrial establishments where the conditions of maintenance and supervision ensure

that only qualified personnel service the installation. They may be installed either in cable trays, raceways, hazardous

locations, as an aerial cable on a messenger, direct burial where identified for the use, under raised floors in rooms

containing industrial equipment, under raised floors in information technology equipment rooms.

ITC cables may not be installed with power, lighting, Class 1 circuits that are not power limited, or non-power limited

circuits unless they have a metallic sheath and or are terminated within equipment or junction boxes or separations

are maintained by insulating barriers.

Even if shielded, both PLTC and ITC cables should be separated from 600-volt power cabling to avoid noise or cross

talk. This is generally accomplished through a barrier strip within the cable tray. Whenever possible it is considered

best practice to route power and instrumentation cables is separate trays.

Type MC-Metal Clad Cables – (NEC Article 330) – Metal Clad cables are assemblies of one or more insulated

circuit conductors with or without optical fiber members enclosed in an armor of interlocking metal tape, or a smooth

corrugated sheath. A plastic overall jacket can also be provided.

In appearance MC cables are very similar to armored clad cables type AC cables. It is important to differentiate the

two as they should not be confused. Type MC cables contain an equipment ground conductor while type AC cables

have an internal bonding strip in contact with the armor. More importantly type MC cables are suitable for outdoor

use while type AC cables are not permitted for outdoor use (wet or damp locations).





Type MC Cables are widely used in 600 volt and MV power, lighting and control applications. They are permitted

for use on services, feeders and branch circuits for power, lighting, control and signaling circuits in accordance with

Article 330 and 725 of the NEC. Type MC Cables may be installed indoors or outdoors, in wet or dry locations,

hazardous locations (Class I, Division I), in cable tray, as aerial cable on a messenger, in any approved raceway, direct

burial (where identified), or encased in concrete (where identified). MC cables are not permitted to be installed where

subject to physical damage. MC cables must be supported and secured at intervals not exceeding six feet.

In many industrial application type MC cables, routed in cable trays, have proven to be an excellent economic

alternative to wire in conduit.

Type MI-Mineral Insulated, Metal Sheathed – (NEC Article 332)- MI cables are a factory assembly of one or more

conductors insulated with a highly compressed refractory mineral insulation, typically magnesium oxide, and enclosed

in a liquidtight and gas tight continuous copper or alloy steel sheath. They can also be provided with an overall plastic

jacket for additional corrosion protection. Developed in the late 1920’s by the French Navy for submarine electrical

wiring systems, properly installed MI cable is commonly considered the safest electrical wiring system available.

Since MI cables use no organic material as insulation (except at the ends), they are more resistant to fires than plastic-

insulated cables. MI cables are used in very high temperature applications and /or critical fire protection applications

such as alarm circuits, fire pumps, and smoke control systems. MI cables have a two-hour fire rating for critical

emergency service and can be used as plenum cabling without an overall nonmetallic jacket. MI cable is also used in

process industries handling flammable fluids where small fires would otherwise cause damage to control or power

Cables. MI cable is also highly resistant to ionizing radiation and are used in applications at nuclear power facilities

and nuclear physics apparatus.

MI cables are suitable for 300 volt and 600 volt applications and are permitted for services, feeders, and branch circuits

for power, lighting, control, and signal circuits. They may be installed in dry, wet or continuously moist locations,

indoor or outdoor, exposed or concealed, Where embedded in plaster, concrete, or other masonry, in hazardous

locations, where exposed to oil or gasoline, in underground runs, or in cable trays.

MI cables are not permitted in underground runs unless protected from physical damage, where necessary. MI cables

are also not permitted where exposed conditions are destructive and corrosive to the metallic sheath, unless additional

protection is provided.

When installed in cable trays MI cable shall comply with NEC Article 392.30(A) ensuring the cable tray is supported

at intervals in accordance with the installation instruction.

Type OFN-OPC- Optical Fiber – (NEC Article 770) – Fiber optic (or “optical fiber”) refers to the medium and the

technology associated with the transmission of information as light impulses along a glass or plastic wire or fiber.

Fiber optic wire carries much more information than conventional copper wire and is far less subject to

electromagnetic interference.





An optical fiber cable is a cable containing one or more optical fibers that are used to carry light. The optical fiber

elements are typically individually coated with plastic layers and contained in a protective tube suitable for the

environment where the cable will be deployed. Different types of cable are used for different applications, for example

long distance or providing a high-speed data connection between different parts of a building.

Optical Fiber (OF) cables are rated as conductive or non-conductive. OF cables rated as conductive contain non-

current carrying members such as a metallic sheath or armor. OF cables rated as non-conductive contain no electrically

conductive materials. They are also rated based upon U.L. flame test(s) and are marked with their respective NEC

building fire rating.

NEC Article 770.113 (H) Permits the following types of optical fiber cables to be supported in cable trays.

OFC: Optical fiber, conductive

OFN: Optical fiber, nonconductive

OFCG: Optical fiber, conductive, general use

OFNG: Optical fiber, nonconductive, general use

OFCP: Optical fiber, conductive, plenum

OFNP: Optical fiber, nonconductive, plenum

OFCR: Optical fiber, conductive, riser

OFNR: Optical fiber, nonconductive, riser

NEC Table 770.154(a) Applications of Listed Optical Fiber Cables details where these types of cables and cable trays

may be used within buildings, and which type of cable may be used in cable trays. In summary:

* Example – The space over a hung ceiling used for environmental area handling purposes.

Note: Where permitted the cables and cable trays must be installed per the installation methods described in 770.110

and 770.113.





OFN (non-conductive) cables are permitted to occupy the same cable tray with conductors for electric light, Class 1,

non-power limiting fire alarm, Type ITC, or medium power net-work powered broadband communications circuits

operating at 1000 volts or less. OFC (conductive) cables must be separated from these other types of cables.

Cable tray fill capacities for optical fiber cables are not addressed in NEC Article 770 nor Article 392. Designers and

installers should refer to the cable manufacturer for guidance.

Type CMP – CMX Communication Cables – (NEC Article 800) similar to optical fiber, communication cables are

used to send information signals. This can be accomplished with coaxial conductors, copper conductors, or twisted

wire pairs. These cables are used in a wide variety of applications, including recording studios, data transmission,

radio transmitters, intercoms, electronic circuits, and in applications where RF shielding is needed. The NEC defines

communication cables as a factory assembly of two or more conductors having an overall covering. A covering over

the conductor assembly may include one or more metallic members, strength members, or jackets. Ethernet cables

are a common type on communication cable and are often listed and installed according to NEC Article 800.

Since communication cables are often routed through air circulation spaces which often contain very few fire barriers,

they need to be coated in material that won’t contribute to the spreading of flames. Communication cables are test by

UL and are (rated) marked based on their fire propagation properties and as such their suitability to be applied in

certain building areas (environmental air-handling spaces).

NEC Article 800 defines these markings, areas of permitted use and provides a hierarchy for cable substation.

NEC Table 800.154 (d), Table 800.179

NEC Table 800.154(a) Applications of Listed Communication Wires and Cable in Buildings Further details the

application for each type of communication cable including, applications where cable trays may be used within

buildings, and which type of cable may be used in cable trays. In summary:






Note: Where permitted the cables and cable trays must be installed per the installation methods described in 800.113.

Type FPL-FPLP (CI), NPLF – NPLFP (CI) Fire Alarm Cables – (NEC Article 760) Fire alarm circuits and cables

are classified as either power limited or non-power limited. Cables for either type circuit may be furthered classified

as (CI) indicating they have meet the requirements to ensure continued operation of critical circuits during a specified

time under fire conditions. Power-Limited-Fire Alarm (PLFA) circuits are fire alarm circuits powered by a source

that complies with 760.121 (listed PLFA or Class 3 transformer, Listed PLFA or Class 3 power supply, listed

equipment marked to identify the PLFA power source.)

As with communication and optic fiber cables, PLFA fire alarm cables are also further marked relative to their fire

propagation potential, indicating the permitted areas of use. There is also a hierarchy for permitted substitution for

cables used in power-limited circuits, which includes communication cables.

Power limited fire alarm cables (FPL-FPLP) are solid or stranded copper. Multi-conductors cannot be less than 26

AWG. Single conductors cannot be less than 18 AWG. FPL cables must have a voltage insulation rating of not less

than 300 volt. Power-limited fire alarm cables are not permitted to be placed in cable trays with electric light, power,

Class 1, non-power limited fire alarm, and medium-power network-powered broadband communication circuits

unless they are separated by a barrier. You cannot install audio system circuits [760.139(D), 640.9(C)] (using Class 2

or Class 3 wiring methods) in the same cable or raceway with PLFA conductors or cables.





NEC Table 760.154 Applications of Listed PLFA Cables in Buildings – details the application for each type of PFLA

cable including applications where cable trays may be used within buildings and which type of cable may be used in

cable trays. In summary:


Note: Where permitted the cables and cable trays must be installed per the installation methods described in 760.130

and 760.145.

Non-Power – Limited Fire Alarm (NPLFA) circuits are fire alarm circuits powered by a source that complies with

NEC 760.41 and 760.43 (power source shall not exceed 600 volts and must contain overcurrent protection devices

(OCPDs). OCPDs must not exceed 7A for 18 AWG or 10A for 16 AWG conductors. You must locate the OCPDs at

the point where the conductor receives its supply.)

As with communication, optic fiber cables, and PLFA cables NPLFA fire alarm cables are also further marked relative

to their fire propagation potential, indicating the permitted areas of use.

Table 760.176(G) NPLFA Cable Markings

Note that Multi-conductor non-power-limited fire alarm circuit cables, Types NPLFP, NPLFR, and NPLF, shall not

be installed in exposed air ducts.





LOAD / SPAN CLASS DESIGNATION (CSA C22.2 #126.1-98)

Span m (ft)

Load kg/m

(lb/ft)

2.4(8) 3.0(10) 3.7(12) 4.9(16) 6.0(20)

37 (25) A

67 (45) D

74 (50) 8A 12A 16A 20A

97 (65) C

112 (75) 8B 12B 16B E

149 (100) 8C 12C 16C 20C

179 (120) D

299 (200) E

Non-power limited fire alarm cables are also solid or stranded copper. Size 18 AWG and 16 AWG conductors are

permitted to be used, provided they supply loads that do not exceed 6 ampere for 18 AWG and 8 ampere for 16 AWG

conductors. Conductors larger than 16 AWG shall not supply loads greater than the ampacities given in NEC 310.15,

as applicable.

NPLFA and Class 1 fire alarm circuits are permitted to occupy the same cable, enclosure or raceway provided all

conductors are insulated for the maximum voltage of any conductor in the enclosure or raceway. Where connected to

the same equipment, power supply and NPFLA circuits are permitted in the same cable, enclosure or raceway.

When installed in cable trays, fire alarm circuit conductors, as well as any tray cable should comply with NEC Article

392 Cable Trays. In particular sections 392.22 (Number of Conductors), 392.60 (Grounding and Bonding), and section

392.80 (Ampacity of Conductors).

Although less commonly used, several other types of cables are permitted to be installed in cable trays. These include:

Type AC, CATV, NM, NMC, NMS, SE, USE and UF. As with the cables discussed in this Bulletin users should refer

to the associated NEC Article for the proper wiring methods for each type of cable.

Section 392.10 (A) also permits various other raceways to be installed in cable tray i.e. EMT, RMC and PVC conduits.

However, generally these types of raceways are more commonly and economically supported with strut products

rather than cable tray.

1. MATERIAL AND FINISH

ALVAND Tray is offered in a variety of material

types and finishes - Galvanized steel, Stainless

Steel, Hot Deep Galvanized, Aluminum, Paint

ready.

Refer to the material and finishes pages for more

detail. Consideration should be given to

environmental concerns, cost and application.

2. TRAY LOAD RATING CLASS

The table to the right is the CSA load/span class

designation. The classes are C1, D1, and E and

you will note that the maximum load rating

varies depending on the class and support

spacing.

Note: C, D and E are the conventional CSA

designations.

8A / B/C, 12A / B/C, 16A / B/C AND 20A / B/C are the traditional NEMA designations.





CODE cable tray systems are manufactured to conform to the standard load classes of CSA as follows:

CSA Class

Designation

CODE

Designation

Side Rail

Height

Rated Load

(Kg / m)

Rated Span

(m)

C1 C 102 97 3

C6 150 97 3

D1 D 115 67 6

D3m 115 67 6

D6 150 67 6

E E 115 112 6

E6 150 112 6

It is important to consider the load your cable tray will endure. Consider the following when calculating the load:

Cable weight, snow, ice and wind.

3. STYLES OF TRAY

There are three different styles of cable tray:

Ladder / Ventilated / Solid

4. SELECT TRAY SIZE WIDTH

AND HEIGHT There are different widths and heights of

Cable tray and what you require will depend

on number, size, and weight of the cables in

the tray.

ALVAND standard widths are available in 5cm, 10cm, 15cm, 20cm, 25cm, 30cm, 35cm, 40cm, 45cm, 50cm, 55cm, 60cm,

65cm, 70cm, 75cm, 80cm, 85cm, 90cm, 95cm, 100cm, 105cm, 110cm and 115cm.

ALVAND standard Height is available for the side rail as follows: 30mm, 40mm, 60mm, 80mm, 100mm, 110mm, 120mm,

150mm, 200mm & 250mm.

5. FITTINGS

Cable tray fittings are designed to change the size or direction of the cable tray. One must consider the Radius of the

bend, whether vertical or horizontal. Standard radius are available in 15cm, 30cm, 60cm, 90cm. Custom sizes can be

factory ordered. Fittings are also used for angle situations and are available in 30°, 45°, 60°, and 90°.

6. CONSIDER THERMAL EXPANSION & CONTRACTION

A cable tray may be affected by thermal expansion and contraction, which must be taken into account during

installation. To determine the number of expansion splice plates you need, decide the length of the straight cable tray

runs and the total difference between the minimum winter and maximum summer temperatures. To function properly,

expansion splice plates require accurate gap settings between trays.

Reference: NEMA VE 2-2000

National Electrical Manufacturers Association 4.3.2. Expansion Splice Plates.

7. CONSIDER ELECTRICAL GROUNDING CAPACITY

The National Electrical Code, Article 392-7 allows cable tray to be used as an equipment conductor.





It is important to note that cable tray is not designed to support personnel.

ALVAND tray is a mechanical support system for cables and is not to be used as a walkway,

lifting apparatus or ladder. The use should display warnings to prevent the use of cable tray

for purposes other than its original intent.





Steel (Pre-Galvanized) & Paint Ready Stainless Steel

Pre-galvanized steel, is produced in a rolling mill by

passing steel coils through molten zinc. These coils are

then slit to size and Fabricated. Fabricated by roll

forming, shearing, punching or forming to produce cable

tray. Using structural quality steel assures that the

material will meet the minimum yield and tensile

strengths of applicable ASTM standards. The corrosion

resistance of steel varies widely with coating and alloy.

The pure zinc (galvanized) coating exhibits a high degree

of galvanized protection to exposed steel such as at

sheared edges.

Galvanized is used in applications to allow for ease of

painting and improved coating adhesion. Galvanized

coating is very hard and not easily scratched during

handling.

Typical application: indoor, low thermal expansion, &

cost effective.

Stainless steel cable trays are fabricated AISI Type 304 or AISI

Type316/316L stainless steel. Both are non-magnetic and

belong to the group called austenitic stainless steels. Like

carbon steel, they exhibit increased strength when cold

worked by roll-forming or bending.

Typical application: chemical, refrigeration, paper and food

applications.

Aluminum

Aluminum cable tray are fabricated from structural grade

“copper free” (marine grade) aluminum extrusions.

Aluminum’s excellent corrosion resistance is due to its

ability to form an aluminum oxide film that when scratched

or cut, reforms the original protective film. Aluminum has

excellent resistance to “weathering” in most outdoor

applications. Aluminum cable trays can perform indefinitely,

with little or no degradation over time, making it ideal for

many wet environments. The resistance to chemicals, indoor

and outdoor, can best be determined by tests conducted by

the user with exposure to the specific conditions for which

it is intended.

Typical application: Indoor & outdoor.

Hot-Dip Galvanized

One of the most important choices when designing a cable

tray system for corrosive or outdoor environments is the

material. Steel cable tray with a Hot-Dip Galvanized after

Fabrication (ASTM A123) finish has been used

successfully for many years.

ALVAND offers a variety of rail heights and weight loads to meet all in field application’s. I-beam construction used

in the design of side rails ensure maximum transverse and longitudinal strength. Extruded aluminum ensure smooth

edges, providing protection for cables.

DESIGN

ALVAND cable tray and fittings are manufactured to CSA standard C22.2 No. 126.1-98 (latest version) from designs

offering unprecedented attention to detail and ease of installation.

All ALVAND designs are symmetrical, achieving maximum strength from minimum mass and feature reinforcing ribs

on the side rail for strength. In addition, ALVAND side rails combined with the low profile rung design, offer the

greatest usable inside height available in the industry.

ALVAND unique connector requires only four fasteners per tray. The speed with which can be installed reduces lab

our costs over competitive coupling devices and ensures swift installation of tray and fittings, while providing continuity

of side rail alignment and strength.

In short, ALVAND careful designs have been engineered from improvements and input from the industry and on

exceeding all existing specifications.





CONSTRUCTION

The configuration used in the design of side rails for ALVAND Aluminum Tray ensures maximum transverse and

longitudinal strength. In ladder and ventilated designs, rung spacing is uniform both between rungs and between

sections. Steel Tray side rails and rungs are continuously roll formed for added strength and to ensure smooth edges to

protect cables. Our steel rungs are slotted to accommodate pipe and cable clamps.

All ALVAND cable tray and fittings ensure optimal strength and bonding characteristics by means of welding. Metal

Inert Gas (M.I.G.) welding is a semi- automatic process using inert-gas shroud over a consumable wire electrode which

transfers current to melt the base material. A filler metal is also added for reinforcement. ALVAND cable trays offer

superior welding strength because our rungs are welded on

Both the front as well as the back of the rungs. This is unique to ALVAND tray and adds additional strength to every

piece of ALVAND tray.

Our side rails and rungs are designed to allow users to attach a UC clamp without drilling or tapping the side rail.

SMOOTH EDGES

All aspects of both tray and rungs feature rounded edges and flat smooth surfaces to prevent damage when in contact

with cables.

FUTURE EXPANSION REQUIREMENTS

Easily add cables to an existing system with barrier tray. Future expansion should always be considered when selecting

a cable tray, and allowance should be made for additional fill area and load capacity.

A minimum of 50% expansion allowance is recommended.

SPACE LIMITATIONS

Any obstacles which could interfere with a cable tray installation should be considered when selecting a cable tray width

and height. Adequate clearances should be allowed for installation of supports and for cable accessibility.

Note: The overall cable tray dimensions typically exceed the nominal tray width and loading depth.

• Standard length is 3m (10ft) & 6m (20ft)

• Depth 100mm (4”), 150mm (6”) and custom

SPECIAL ORDERS

ALVAND cable tray systems have been designed to easily accept special orders to suit the specification of your job.

From connectors to join ALVAND tray to competitive products, to custom tray widths, to covers for any cable tray

system on the market. Our manufacturing facility has full CAD design and CNC

Punching and forming capabilities. ALVAND’s customer service staff will handle your request for quotation and

delivery lead times quickly and efficiently there is nothing “too custom”!





Accessories

A component that is used to supplement the function of a straight Section or fitting. Examples include, but are not

limited to, dropout, cover, conduit adapter, hold-down devices, and barrier strip.

Barrier Strip

To separate cables carrying dissimilar voltages.

Cable Tray Support Span

The distance between the centerlines of supports.

Cable Tray System

A unit or assembly of units or sections, and associated fittings, forming a mechanical system used to support cable and

raceways.

Channel Cable Tray

A fabricated structure consisting of a one-piece ventilated bottom or solid bottom channel section.

Connector A component that joins a combination of cable tray straight sections and fittings. The basic types of connectors include rigid,

expansion, adjustable, and reducer.

Fitting

A component that is used to change the size, direction, elevation or width of a cable tray system. Fittings are not subject

to NEMA/ C.S.A. load ratings.

Galvanic Corrosion

Galvanic corrosion results from the electrochemical reaction that occurs in the presence of an electrolyte when two

dissimilar metals are in contact.

Horizontal Cross

A fitting that joins cable trays in four directions at 90 degree intervals in the same plane.

Horizontal Elbow

A fitting that changes the direction of cable tray on the same plane.

Horizontal Tee

A fitting that joins cable trays in three directions at 90 degree intervals in the same plane.

Instrumentation Channel

One-piece channel section; solid or ventilated. Typically used to carry instrumentation, control, data, telephone, or

cables.

Ladder Cable Tray

A fabricated structure consisting of two longitudinal side rails connected by individual transverse members (rungs).

Reducer

A fitting that joins cable trays of different widths in the same plane.

Reducer Left-hand

A reducer; when viewed from the large end, a straight side on the left.

Reducer Right-hand

A reducer; when viewed from the large end, has a straight side on the right.





Reducer Straight

A reducer; two symmetrical offset sides.

Solid-Bottom

A fabricated structure consisting of a one-piece solid bottom channel section that may include louvers on the

bottom face.

Straight Section

A length of cable tray that has no change in direction or size.

Support

A component that provided a means for supporting a cable tray, including, but not limited to, cantilever bracket,

trapeze, and individual rod suspension.

Thermal Expansion & Contraction

Accurate gap setting at time of installation when using expansion connectors.

Trough or Ventilated Cable

A fabricated structure consisting of integral or separate longitudinal rails and a bottom having openings sufficient

for the passage of air and utilizing 75% or less of the plane area of the surface to support cables. The maximum

spacing between cable support surfaces of transverse elements do not exceed 100mm in the direction parallel to

the tray side rails. (On horizontal bends only, the maximum distance between transverse elements is measured at

the centerline of the bend.)

Vertical Elbow

A fitting that changes the direction of cable tray upward or downward from the horizontal plane.

Vertical Inside Elbow

A fitting that changes the direction of cable tray upward from the horizontal plane.

Vertical Outside Elbow

A fitting that changes direction of cable tray downward from the horizontal plane.

Vertical Tee

A fitting that joins cable trays in three directions at 90 degree intervals in different planes.

DISCLAIMER: Ensure ladder tray system performs as designed, it is important that it is properly installed. Everything must be

done in accordance Occupational Health & Safety procedures, as well as local and customer building codes.

WARRANTY: In the event a product is deemed defective to ALVAND, such products shall be repaired. Repair is at the discretion

of ALVAND. Under no circumstances will a credit be issued for unauthorized rework of any materials.





ERRORS, OMMISSION, & CORRECTIONS: The ALVAND catalogue’s price list, website, flyers, and any other

printed or electronic literature are subject to errors and omissions. Data included in the material is subject to change without notice. All

literature is updated as needed and posted online at www.alvand-co.com. This information is updated at ALVAND’s discretion.

Unit 1, No 1, Khayyam Alley, Motalebi nejhad St, Akhlaghi St, Dolat St,

Tehran, Iran.

Tel: +98(21) 22-64-6197, (21) 22-64-6198, Fax: +98(21) 22-64-2789

Telegram/WhatsApp: +98-903-271-8946

Email: [email protected] , Website: www.alvand-co.com



