Cables - Cable for Petrochemical Plants IEEESTANDARD1242

8/2/2019 Cables - Cable for Petrochemical Plants IEEESTANDARD1242

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BY D O N A LD A . V O LTZ & JO SEPH H. SN O W

HE PURPOSE OF THIS

ARTICLE is to provide an

overview of IEEE 1242-

1999, Guide for Specifying

and Selecting Power, Control, and Special Pur-

pose Cable for Petroleum and Chemical Plants. This standard

addresses wire and cable design, materials, testing, and

installation, along with illustrations of typical construc-

tions and application criteria. An extensive cross-refer-

enced list of standards and technical papers, as they apply

to thewire andcable industry, is includedin theappendixof the standard.

Background

A paper titledWireand CableUpdate 1990

[1] was presented at the1990 Petroleumand

Chemical IndustryCommittee (PCIC) Con-

ference in Houston, Texas, USA. During

the writing of the paper, the authors con-

cluded that the information it contained

could possibly form the basis of a PCIC

Working Group (WG) to address the speci-

fication and selection of cable in the petro-

chemical industry. Since the authors were

members of both the IAS/PCIC and the

PES/Insulated Conductors Committee

(ICC), there would be a possibility of get-

ting input not only from the user commu-

nity, but also from the manufacturing and

consulting communities. Therefore, a

joint WG between PCIC and ICC was

formed, andworkproceeded on theguide.

The final draft from the WG was sub-

mitted to IEEE for balloting in February 1998. After the

resolution of negatives and coordinating society com-

ments, a new draft was balloted and the IEEE Standards

Activities Board approved the guide in June 1999.

The guide contains useful information on the specifica-

tion and selection of power, control, and special-purpose ca-ble typically used in petroleum, chemical, and similar type

plants. It addresses those topics that are peculiar to the pet-

rochemical industry. However, it includes many re-

cent developments, such as strand filling;

low-smoke, zero-halogen materials; water

swellable tapes; chemical-moisture barriers;

and cable testing. This guide is intended to

help the user in developing specifications for

cable constructions by addressing industry

standards in conjunction with those problems

peculiar to the petrochemical industry.

The guide provides the user with perti-

nent information on cable designs, applica-

tions, and the latest test procedures. It is

intended to be an informational tool for the

new, as well as the more seasoned, engineer.

In this capacity, it contains an extensive ref-

What s in it,and HOW w ill it

help you?T

1077-2618/ 02/ $17.002002 IEEE


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erenceand cross-reference listingof cablestandards, including those from theUnited States, Canada, and some fromEurope. Illustrations and tables are pro-vided with a correlation to applicable in-dustry standards for cable constructions.Application guidelines are provided forthe type of installations found in thepet-

rochemical industry as they relate toelectrical,mechanical, physical, thermal,and environmental properties of the ca-ble. The use of this guide should help toeliminateprematurecable failures duetoimproper cable specification, selection,and application.

The following major headings in thisarticle bear the same title as the applica-blemajor clauses contained in the guide.Under these headings is a summary ofcontent that should beof benefit to thoseevaluating the scope and need for thispublication. The applicable clause num-

ber from theguideis shown,in parenthe-sis, after the heading.

Typical Constructions (Clause 3)This clause provides detailed information on various low-and medium-voltage cable constructions that are typicallyused in petroleum and chemical plants. Thereare 19 figuresthat provide photographicillustrations alongwith text, giv-ing specifics of the cable components, applicable standards,conductor temperature range, flame ratings, and applica-tions. Fig. 1 is a typical example of these illustrations.

Application Guidelines (Clause 4)This clause provides an overview of the many factors to be

considered in selecting a cabling system for a petroleum orchemical plant. Additional details on many of these mat-ters are addressed in subsequent clauses.

Types of Installations

Thesize andelectrical load forthefacility,the geographic layout, environmental as-pects, and the electrical service supply areamong the first considerations. Decisionson these matters are made early in the en-gineering program. After project criteriaisdetermined,a decisiononthe typeofca-

ble installation, whether underground oroverhead, can be made. Each system hasits merits. The trend seems to bemore to-ward tray systems (Fig. 2), although un-derground systems are often selectedwhere severe weather, fire hazard, or envi-ronmental conditions present a hazard tooverhead systems.

Underground cabling systems arenormally either direct buried (Fig. 3) orinstalled in ducts (Fig. 4). Either typeprovides protection from wind, explo-sions, fire, or accidental contact fromcranes or other construction equipment.

However, exposure to ground water andchemical contamination may warrant ca-

ble designs that provide protection from such deleteriouselements, as well as additional mechanical protection inthe case of direct buried cables.

Overhead, supported cabling systems are initially lesscostly and easier to maintain, modify, or replace. A typicalexample of an overhead messenger supported cable systemis shown in Fig. 5.

Electrica l Considerations

Resistance to voltage breakdown, due to peak transientvoltages, of any electrical distribution system is a functionof its design basic impulse level (BIL) of equipment and its

connecting cabling plus thethermal aging characteristic ofthe cable. The insulation of the cable selected, and itsthickness, must be compatible with the rated operating

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Construction:

Applicable Standards:

Conductor Temperature:

Flame Rating:

Applications:

Remarks:

A - Conductor: Copper, bare, soft, Class B, concentric stranded per ASTM B-8 (Alum available)B - Strand Screen: Extruded thermoset semi-conducting EPR or polyolefinC - Insulation: EPR, XLPE or TRXLPED - Insulation screen: Extruded semi-conducting EPR or polyolefinE - Shield: Helically applied overlapped copper tape or helical wire shieldF - Jacket: PVC or CPE (Thermoplastic), CSPE, CPE (Thermoset) or LSZH

AEIC CS-8, ICEA S-93-639/NEMA SC74, ICEA S-97-682,

UL 1072, CAN/CSA C68.3

90 C wet or dry, 105 C available in EPR

Normally capable of passing vertical flame test per UL1581 or IEEE 1202. Must beapproved for CT use if installed in tray per UL 1072 option.

Raceways, ducts, direct burial, messenger and tray subject to NEC and CSA restrictions.

Requires Stress cone terminations. Give tree retardancy consideration when selectinginsulation for underground applications

A

B

C

D

E

F

535 kV, Type MV- 90, 1/ C, helica l tape or wire shield.

1

THE GUIDE

PROVIDES THE

USER WITH

PERTINENT

INFORMATION

ON CABLE

DESIGNS,

APPLICATIONS,

AND THE LATEST

TEST

PROCEDURES.


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voltage of the system, as well as the BIL level of the sourceand utilization end equipment.

Ampacity determination includes consideration ofmany factors that are listed in the guide. Normally, Na-tional Electrical Code (NEC) tables are most often used.However, underproper engineering supervision, ampacitymay be determined by use of the Neher-McGrath method.References to these methods are provided.

Methods for selecting grounding conductors for neutral,system, and equipment are included in this clause, as well asfault current ratings of conductors and metallic shields.

Mechanica l and Physical Considerations

The sheaths or coverings used over other cable materials toprotect the cable components from environmental and in-stallation conditions can greatly affect the overall life cycleeconomicsof thecable system. Both metallic andnonmetal-lic materials, or a combination of these coverings, are avail-able toprovide theprotection needed forspecific conditions.Some of these specific conditions include the effect of ro-

dents, insects, abrasion, impact,moisture, acids, alkalis, andother chemicals. The sheaths or coverings may be applied asprotection over single conductors or over multiple conduc-tors. Different types of coverings and sheaths are outlined inthe guide with references containing further information.

Environmental Considerations

The effect of the cable on its surroundings must be consid-ered in response to the increased awareness of environmen-tal issues. The potential for arc flash, explosion, firepropagation, smoke, and the emission of toxic and/or cor-rosivegasesmust be considered in theapplication andloca-tion of the cable. Also, the effect of the environment on thecable must be considered. Specific topics covered include

hazardous areas, fire safety considerations, flame spread,smoke measurement, corrosivity, toxicity, and cold tem-perature installation.

Conductors (Clause 5)This clause reviews conductor materials and stranding. Thetwo most common conductor materials used are copper andaluminum.The NECrequires conductors to be stranded forsizes 8 AWG and larger. Stranded conductors are typicallymade more flexible by increasing the number ofwires in theconductor. The size specified for the conductor in AWG,kcmil, ormm2 denotes the total area of theconductor metal.Factorsto consider in selectingcopperor aluminumconduc-

tors are addressed, along with information on tinned or leadalloy-coated copper and filled-strand conductors.

Insulation (Clause 6)

Ma terials and Thickness Available,

Low Voltage (0-2,000 V)

The most readily available insulations for low-voltage ca-bles are polyvinyl chloride (PVC), crosslinked polyethyl-ene (XLPE), and ethylene propylene rubber (EP, EPR, orEPDM). Chlorosulphonated polyethylene (CSPE), chlori-nated polyethylene (CPE), and polyamide (Nylon) aresometimes used for the second layer insulation/jacket indual-layer extrusions for mechanical protection. The tem-

perature rating of such materials is usually 75 C for ther-moplastic materials and 90 C for thermoset materials.

The insulation type andinsulation thicknessofwire andcable used in petrochemical plant applications are usuallyset by industry standards written by UnderwritersLaborataory (UL), the Canadian Electrical Code (CSA), orthe National Electrical Manufacturers Association(NEMA)/Insulated Cable Engineers Association (ICEA).In the United States, virtually all wire and cable used inpetrochemical plantsare required tobe installedin compli-ance with the NEC (see NFPA 70-2002). In Canada, wireand cable must be installed in compliance with CSA

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Cable tray system.

2

Underground duct system.

4

Underground direct buried system.

3


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C22.1. What this means, in a practical sense, is that thewire or cable must bear the proper UL or CSA marking forthe application. It must also be installed in a manner con-sistent with thecode requirementsapplicable to thepartic-ular facility in which the wire or cable is being used.

Tables are included in Clause 6 to provide insulationthickness data for both single- and multiconductorlow-voltage cables of various constructions.

Ma terials and Thickness Available,

Medium Voltage (5-35 kV)

Insulation types and thicknesses for MV cables are estab-lished by UL, CSA, NEMA/ICEA, and the Association ofEdison Illuminating Companies (AEIC) standards. Themost predominate insulation materials are XLPE, tree re-tardant crosslinked polyethylene (TRXLPE), and EP,EPR, or EPDM.However, low- andmedium-densitypoly-ethylene can be used for some applications.

The cable insulation level required for an MV applica-tion depends on the neutral grounding type (e.g., solidlyor impedance grounded) and the intended mode of plantoperation (e.g., maximum equipment protection withfast tripping or minimum process interruption withtime-delayedtripping). Insulation levels of 100,133,and173% are defined in Clause 4. On critical circuits wheremaximum reliability is required, the use of thicker insu-lation is recommended.

Tables are included that list insulation thicknesses forsome of the more common shielded MV cable construc-tions, along withtheapplicableindustry standards.Insula-tion thicknesses for nonshielded MV cable, other voltageratings, and conductor sizes larger than 506.7 mm

2(1,000

kcmil) can also be found in the standards referenced. Across-section of a typical MV shielded cable is shown inFig. 6.

Performance Requirements

Insulating materials have improvedover theyears andnowprovide the specifying engineer with a wide range of prop-erties that enable an optimum match to a particular appli-cation. The choice of insulation will depend on manyfactors, such as the operating voltage and temperature, thetype (signal orpower)and frequencyof electric energyto betransmitted by the conductor, the type of outer protectivecovering for the insulation, the amount of flexibility de-sired, outside chemical influences, etc. Where a number ofinsulationmaterialsaredeemed suitable for an application,selection may be made based on economics, maintenance,or other factors. In any case, it is important to consider the

minimum acceptable performance characteristics of an in-sulation to assure the long-term reliability of an electricalsystem. The following properties should be considered inevaluating insulating materials:n dielectric strengthn capacitancen thermal characteristics and heat dissipationn power factor (dissipation factor), insulation resis-

tance, and lossesn resistance to water treeingn physical properties, chemical resistance, and envi-

ronmental considerations.

The choice of materials for the cable design will dependon thedegreeof abuse it is subjectedto,or theenvironmentin which it is being designed to operate. However, theoverriding choice of a specific material will depend on itsdielectric properties or degree of reliability required.

Shielding (Clause 7)Many low-voltage cables and most MV cables, as well as

certain special-purpose cables, require some form of elec-trical shielding. Clause 7 provides the user with many de-tails on shielding selection and application. Some systemcharacteristics that should be considered in determiningthe need for shielding are the functioning of overcurrentdevices, required levels of fault or surge current, the man-ner in which the system may be grounded, desired levels ofelectrostatic protection, and environmental factors, suchasincidenceof lightning. It is recommended that cablesoper-ating at 4-kV and above be shielded.

Environmental Considerations

There are environmental considerations that are impor-tant to overall cable operation and may have an affect di-

rectly or indirectly on the shielding. One of the keyconsiderations is ambient temperature and its affect oncurrent-carrying capacity. A second is location, i.e., in-doors, outdoors, or underground. All three locationshave specific thermal characteristics that affect cableampacityand potential shielding requirements. Specific

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Overhead messenger supported system.

5

Shielded MV Cable

Conductor Shield

Insulation

Insulation Shield

Metallic Shield

Protective Jacket

Typica l MV shielded cable.

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environmental considerations affect-ing shielding choices are corrosion andwet locations.

Electrica l Considerations

There are several electrical system pa-rameters to considerwhenusingshieldedcable. Among these are the following:

n fault currentsn voltage considerationsn splicing devices and techniquesn grounding of shieldsn shield lossesn insulating barriers in the shield.

Semiconducting Ma terials

These materials are used in MV cable toform a conductive bridge from eithertheconductor to theinside surface of theinsulation or from the outer surface ofthe insulation to the metallic shield.The function is to prevent voids and en-

sure an even distribution of the electri-c a l s t r e s s . T h e f o r m u l a t i o n o f semiconductive materials require the use of largeamounts of conductive carbonblack, which is usually dis-persed in a suitable polyolefin, EP, or butyl acetate com-pound. In addition to the principal constituents, minoramounts of proprietary additives are included to aid dis-persion, heat stability, and adhesion to the insulation.The properties of these materials vary depending onwhether they areformulatedfor strandshielding or for in-sulation shielding.

Metallic Shielding Materials

Cable shields arenonmagnetic metallic materials. Thetwomaterials typically used for metallic shields are aluminumand copper. Aluminum requires a larger diameter as a wireor a thicker cross section as tape to carry the samecurrent ascopper. At equivalentcurrent-carrying capacity, an alumi-num shield will be lighter in weight but about 40% largerin dimensions. Aluminum shields are used for instrumen-tation, control, and communication cables, while coppershields are used with medium- and high-voltage cables.

The metallic shield needs to be electrically continuousover a cable length to adequately perform its functions ofelectrostatic protection, electromagnetic protection, andprotection from transients, such as lightning and surge or

fault currents.A nonmetallic covering or jacket may be used over theshield for mechanical and corrosion protection. The cover-ing must prevent exposure of the metallic shield duringhandling and installation. It is important to ensure thatcontinuity of the metallic shield will notbe broken duringhandling, installation, or operation.

Current Carrying Capability

The ability of a metallic shield or sheath to carry currentis a function of its resistance. The lower the resistance,the more current it can handle at a given temperature.

Guidelines for the minimum amount ofshield conductance required are given inICEA standards.

It is necessary to consider the shortcircuit current (capacity) of the shield toassure the cable will not be damaged dueto the heat generated during a fault.

Also to be considered is induced

shield voltage. Circuits that employshielded, single-conductor cable carry-ing alternating current will encounter avoltage buildup on the shield if theshield is grounded at only one point. Theguide provides formulas for use in calcu-lating the induced shield voltage for sev-eral cable arrangements.

Cable Jackets (Clause 8)Cables in petrochemical plants are ex-posed to many different environments.Thus, thefunctionof a jacketis toprotectthe underlying cable components from

one or a number of exposures, includingmechanical abuse, chemicals, flame,

moisture, sunlight, and other radiation. Table 1 has beenextracted from Clause 8 as an example. Basic properties ofjackets used on cables in the petroleum and chemical in-dustry are shown in this table.

The thickness of cable jackets depends primarily on thetypeof cable and the diameter ofthe core. Ingeneral, jacketthickness is specified in theapplicableindustrystandards.

The following are the major electrical property con-siderations to be taken into account in selectingjacketing materials:n Dielectric Strength: Cable jackets may be semicon-

ducting or insulating. If insulating, a fair rangeofdi-electric strengths are available.

n Discharge and Tracking Resistance: When anonshieldedcable rests uponor comes into contactwith a ground plane, the ground plane acts as theouter plate of the capacitor, made up of the con-ductor, insulation and the ground plane. Dis-charges and tracking may cause erosion of thejacket material.

The physical properties of jackets is a major issue sinceprotection from mechanical abuse during and after instal-lation is the primary jacket function. Key considerationsare toughness and flexibility.

A major consideration in selecting a jacket is whether a

thermoplastic or thermosetting material is required. Inmost cases, a thermoplastic jacket is less expensive. How-ever, thermoplastics will melt at some elevated tempera-ture (different for each thermoplastic material) and, thus,could run or drip from the cable under extreme conditions.This may be unacceptable in many applications.Thermoset materials will not melt and run or drip at ele-vated temperatures.

Chemical, environmental, and flame properties mustalso be takenunderconsideration to include thefollowing:n Chemical Resistance: Theresistance of jacket materials

to various chemicals can be of major importance.

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THE USE OF THIS

GUIDE SHOULD

HELP ELIMINATE

PREMATURE

CABLE FAILURES

DUE TO

IMPROPER

CABLE

SPECIFICATION,

SELECTION, AND

APPLICATION.


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n Moisture Resistance: Moisture is a major considerationin all underground installations and many otherplant locations. Thus, cable jackets and construc-tions that resist moisture should be considered forsuch applications.

n Flame Resistance: Therelativedegree towhicha jacketmaterial will burn is an important consideration injacket selection. The importance is dependenton the

application. The guide provides considerable infor-mation on this topic.

n Smoke Density: Obscured vision due to smoke gener-ated by a fire can hinder escape and firefighting ef-forts. This can be a major consideration in workareas, control rooms, or where the public congre-gates. New and improved materials that have low orlimited smoke emissionswhen burnedarenowavail-able. Their use is growing rapidly.

n Toxicity: Many common materials emit toxic sub-stances when burned. This can also reduce the escapepotential ofpersons inthe area ofthe fire. Low orzerohalogen flame retardant compounds are available toaddress this problem.

n Corrosivity: Many materials emit corrosives whenburned. This may be further complicated if the cor-rosives react with firefighting agents, such as water,

to form acids or bases.Onesuch well-known reactioninvolves the combination of hydrogen chloride withwater to form hydrochloric acid.

One other issue that must be considered is the futuredisposal of used cables. Some jacket compounds containvarying quantities of toxic materials, such as lead oxide,that may present future disposal problems from an envi-ronmental point of view.

Moisture and Chemical Protection (Clause 9)There is a need forchemical andmoisture protection forca-bles used in petrochemical plants, especially in under-ground applications. The environment in these plants canhave an adverse effect on cable materials, potentially lead-ing to less than expected performance. The various meth-odsused toprovide protection from theeffects of chemicalsand moisture are described in this clause. These methodsare listed as follows:n choice of jacketing materialsn use of chemical/moisture barrier (CMB) cables with

laminate sheathsn use of metallic sheaths as CMBsn use of water blocking materials in cables.When metallic shields and armors are used for moisture

protection, suitable jackets over the shield are needed to

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TABLE 1. PROPERTIES OF CABLE JACKETS

PropertiesThermop lastic Thermoset

PE PVC CPE CSPE/ NEO CPE

Physic a l

Toughness Exc ellent Good Excellent Excellent Exc ellent

Flexib ility Poor Good Good Excellent Exc ellent

Ease of insta lla tion Good Exc ellent Excellent Good Good

Thermal

Thermal rating, dry 75 C 60-90 C 60-90 C 90 C 90 C

Thermal stab ility Poor Good Good Excellent Exc ellent

Heat resista nc e Good Exc ellent Exc ellent Exc ellent Exc ellent

Chemica l Resista nc e

Ac ids Exc ellent Exc ellent Good Excellent Exc ellent

Alka lines Exc ellent Exc ellent Good Excellent Exc ellent

Organic solvents Exc ellent Poor Good Good Good

Oil Poor Fa ir-good Fa irgood Good Good

Water Exc ellent Good Good Good Good

Spec ial Properties

Flame resistance Poo r Good -exce llent G ood -exce llent Exce llent Exce llent

Wea ther resista nc e Exc ellent Goo d Exc ellent Exc ellent Exc ellent

NOTE: These comp arisons a re general in nature. Spe c ific fo rmulations and c om po und va ria tions of these mat erials will

cha nge the performanc e c riteria to some extent.


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provide corrosion protection.Alternatively, protective coat-ings on the shielding materials and/or cathodic protectionmay be considered. Corrosion can generate pin holes and/orother openings in the metallic sheath. These openings willgreatly compromise the chemical or moisture barrier.

The major topics covered in this clause and brief re-marks on key points follow.n Moisture Resistance of Jackets: No polymeric material

can absolutely prevent the permeation of moisture.All have a defined moisture permeability that de-pends onthe composition of the jacket and the mate-rials that areused as additivesor fillers to thejacket.

n Chemical Resistance of Jackets: The effects of chemicalsand oils can cause hardening, softening, swelling,and/or cracking of polymeric jackets.

n Laminate Sheaths: Using such sheaths as chemi-cal/moisture barriers is another option. The laminatesheath consists of a plastic-coated metallic tapebonded to the overall (outer) cable jacket, as shownin Fig. 7. The tape may be coated on one or bothsides.Thetape is longitudinally foldedwith an over-lapat theedges.Duringthe jacket extrusionprocess,

the coating melts and bonds to the jacket, and thecoatings in the overlap form a seal that resists mois-ture andchemicalpenetration.In additiontoprovid-ing chemical and moisture protection, this type ofsheath, with an aluminum substrate, is commonlyused for instrument and low-voltage control cable to

provide electromagnetic interference (EMI) shield-ingand lightningprotection.This type of sheath, us-ing copper, has been used for undergroundapplications of MV power cable to provide shieldingas well as a CMB.

Extruded lead and aluminum sheaths can also be used asmoisture or chemical barriers. Metallic sheaths with weldedseams and lateral corrugations have likewise been used.

Water blocking is a means for preventing moisture mi-gration. Methods to be considered are as follows:n Powders: Swellable powders are used as longitudinal

water blocks in cables to prevent longitudinal waterpenetration. These powders swell and expand suffi-ciently upon contact with water to form a gel-likematerial to block the flow of water.

n Water-Blocking Tapes: A water-blocking tape is usu-ally a nonwoven synthetic textile tape impregnatedwith, or otherwise containing, a swellable powder.

n Sealed Overlap: To ensure a seal of the overlap,hot-melt adhesives can be used. These adhesives canbe extruded or pumped into the overlap seam of alongitudinally formed metallic tape before the seamis closed during cable manufacture.

Metal Armors (Clause 10)Metallic armored cables are used to provide additional me-chanical protection, increase resistance to flame propaga-tion, and provide a barrier to the intrusion of moisture andchemicals. The most common type of armored cable usedin the petrochemical industry is a continuous corrugatedaluminum, metal-clad (Type MC), cable, as shown in Fig.8. The self-contained cable system of metal clad cable pro-vides a factory installed system without subjecting theindividual insulatedconductorsto the possiblemechanicaldamage of installation, as they would be if pulled as single

conductors into a conduit or cable tray.Permitted uses, installation and construction specifica-tions for Type MC cable are covered in Article 330 of theNEC. Canadian armored cables are manufactured andtested in accordance with CAN/CSA C22.2 No. 131. ForUL label requirements, the constructions for 600- and2,000-V cables are given in UL 1569. While MV types arecovered by UL 1072. Typical requirements for sheaths, in-terlockedarmor, flat tape armor, andround wire armoring,including required bedding and covering, appear in speci-fications such as ICEA S-93-639 (NEMA WC 74).Metal-clad cables, for use in Class 1, Division 1 hazardousareas, have increased mechanical properties and specificgrounding requirements, as set forth in UL 2225 and

CAN/CSA C22.2 No. 131. UL identifies such cables asType MC-HL.The various types of metal armors, including the key fea-

tures for each type of armor, are listed in the tables of Clause10.Descriptions,materials andapplications arealso covered.

Cable Quality and Testing (Clause 11)Historically, general design parameters for wire and cablewere developed by cable manufacturers and users. Cur-rently, readily available specifications based upon industryand national standards provide design parameters andquality requirements. Comprehensive designs, utilizing66

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The Bonded Jacket,Sealed Seam Sheath

Bonded Jacket:Mechanical Strength

Two Side Coated Metal:Corrosion ProtectionSealed Seam:

Chemical/Moisture Barrier

Typica l laminate shea th.

7

Typica l metal-clad , Type TC ca ble.

8


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strand filling, super smooth semiconductingscreens, extraclean insulation, swellable moisture sealing materials, andmetal/plastic laminate shielding and sheathing, are ex-tending cable life.

Quality assurance principles used in the wire and cableindustry provide a basis for evaluating acceptable electri-cal, chemical, and physical properties for these products.As a result, quality assurance programs influence and im-

pact thedesign,manufacture,andinstallation ofpowerandcontrol cables and have a significant effect on service life.

Achieving desired quality during the manufacture ofany cable or cable assembly is dependent upon the use ofhigh-quality materials and state-of-the-art processes forsuch categories as:n raw materialsn handlingn compoundingn extrusion technologyn curing processesn acceptance testing.Programs to assure quality and cable conformance are

normally adopted by a manufacturer to ensure full confor-mance to applicable standards.Other topics relating to quality and testing included in

Clause 11 are:n Application of Standardsn Testing Programsn Factory Testsn Field Acceptance Testsn Maintenance Testsn Special Testsn Reports and Documentationn Interpretation of Results.Reference to these topics will provide much additional

informationonsteps to insurethereceipt ofquality cable aswell as tests after installation.

Specia l-Purpose Cables (Clause 12)Clause12 of theguide includes information on special pur-pose cables used in petrochemical plants that are outsidethe power and control categories covered in Clause 3.

Instrument Cable

Included in this categoryaresingleandmulticonductorin-strumentation cables, as well as thermocouple extensioncables. Instrumentation cables are either single ormulticonductor cables comprised of twisted pairs or triadsthat convey low-energy or power-limited electrical signals

from field devices to process analyzers, controllers, or someform ofdistributed control system(DCS). These signals areused to control andmonitor equipment in process facilitiesand electric power systems. They function as the electricalpathway for connecting thenonmechanical elements of thefeedback control loop to the input and output devices.

Circuit Classifica tions

Class 1,2, and3 circuit conductors aredescribed, andrefer-ences are made to applicable NEC articles. Wiring meth-ods, installation, and other related information on thesetypes of circuits is provided.

Cable Descriptions and Types

The following types of instrument cable are described indetail and cross referenced to applicable NEC articles, to-gether with application information:n 300-V power limited tray cable, Type PLTCn 300-V instrumentation tray cable, Type ITCn 600-V tray cable, Type TCn Thermocouple extension cable, Types PLTC, ITC,

and TC.

Fiber-Optic Cables

Fiber-optic cables have been developed in recent years andhave gained rapid acceptance. Now, such cables are in de-mand as a necessity for high-speed communication anddata transmission. Fiber-optic cables have properties thatare very different, and superior in many respects, whencompared to metallic conductor cables.

Thefollowing topics are included for fiber-optic cables:n constructionn core/cladding design

n multimode step-index

n single-mode step-indexn multimode graded-index

n terminations.

Coaxial Cables

Coaxial cables also see frequent use. They consist of a con-ductor centered inside a metallic tube, braid,or shield sep-arated by a dielectric. The inner conductor is typicallyreferred to as the conductor or center conductor. The outerconductor is typically referred to as the shield. Coaxial ca-bles typically have a jacket over the shield. Coaxial cablesare normally used for closed-circuit TV systems, computernetwork cables, security systems, etc.

Voice and Data Cables

Voice and data cables are used for many purposes in indus-trial applications.

Premise Cables

Premise telephone and data cables are generally suppliedwith two, three,or four conductorpairs forruns to individ-ual telephones or with eight, 12, 25, 50, 100, or 200 pairsfor distribution purposes. Cable construction often in-cludes twisted pair, 24-gauge, bare copper conductors;color-coded, polyethylene insulation; and a PVC jacket.For plenum use, fluoropolymer materials are normally uti-lized to minimize fire risk. Largerconductorsizes areavail-

able. For data transmission, cables rated as Category 5, orhigher, should be considered.

Outside Plant Ca bles

Outside plant cables are generally installed aerially, inducts, or direct buried and provide the means for connect-ingcentral office switchingfacilitiesto buildingsand plantfacilities throughout the complex. Such cables are often re-ferred to as exchange cables. Frequently, they are furnishedand installed by local telephone companies. There aremany types, such as air core, filled core, self support, andaluminum, steel, polyethylene (ASP) sheath. 67

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Intercom a nd Audio Cables

Intercom and audio cables are available in numerous con-structions. The typical types are one or two pair, onethrough eight individual conductors, and some combina-tion of pairs and individual conductors. Some of the indi-vidual conductor cables may have conductors of differentsize within the same cable.

Cables for Hazardous AreasCables for hazardous areas must be carefully selected tomeet NEC requirements. In the petroleum and chemicalindustries, hazardous materials are predominantly flam-mable or combustible gases, vapors, and liquids. The ac-ceptabilityof cables in hazardousareas depends notonly onthe type of cable, but also on the type of circuit they sup-port and the type of installation method employed.

Type s of Cab les

Most cables arenotdesigned to prevent flammable or com-bustible gases, vapors, or liquids from migrating throughcable fillers andbetween conductors from a hazardous loca-tion to a nonhazardous location. Thus, sealing require-

ments differ, depending upon the type of cable selected. Alisting of the types of cables most often used in hazardousareas follows:n Mi ne ral -Ins ul at e d Cabl e s : Mineral-insulated,

metal-sheathed (Type MI) cable is a factory assem-bly of oneor more conductors insulated with highlycompacted mineral insulation and enclosed in aseamless, liquid-and-gas-tight continuous copperor alloy-steel sheath. MI cable, due to its construc-tion, has an inherent ability to block gases, vapors,and liquids.

n Metal-Clad Cables: The metal-clad (Type MC) cableis a factory assembly of one or more insulated circuitconductors enclosed ina metallic sheathof interlock-

ing tape, or a smooth or corrugated tube, with orwithout an overall jacketof suitable polymericmate-rial and separate grounding conductors.

n Other Cables: Unlike Type MIcable, other types of ca-bles do not block the passage of flammable or com-bustible gases, vapors, or liquids. Therefore,conduits and seals must be used on cables to preventthe passage of such gases, vapors and liquids.

Types of Circuits

Sometimes, it is the type of circuit a cable supports thatdetermines whether a cable is suitable for installation inhazardous areas. Two basic types of circuits exist: in acircuit type that has enough energy to ignite flammableor explosive gas or vapor mixture during faulted condi-tionsand a circuit type that does not have enoughenergyto ignite hazardous gas or vapor mixture during faulted

conditions. Circuit types that do not have enough en-ergy to ignite are called intrinsically safe and non-incendive circuits.

Types of Cable Installation Methods

When the type of cable or the type of circuit it supportsdoes not qualify for installation in a hazardous area, othermeansof reducing theriskof startinga fire or an explosionareused. Typically, if thecables arenot suitable forinstal-lation in hazardous areas, they must be installed in con-duit and properly sealed with approved fittings. Somecable types, however, are approved for installation inClass I, Division 2 and Zone 2 hazardous areas without

conduit when an approved cable termination fitting isused on each end of the cable. These types include MV,MC, TC, PLTC, and ITC.

Cablebus

Cablebus is another way to utilize insulated cable for highampacity transitions.The most common busway used inthe petrochemical industry is nonsegregated phase,metal-enclosed bus, commonly called bus duct. However,when the bus duct runs are long and the currents high, thecosts and installation of the bus duct, including supports,has proved to be expensive compared to other cable instal-lation methods.

As defined by the NEC, cablebus is an approved as-

sembly of insulated conductors with fittings and conduc-tor terminations in a completely enclosed, ventilated,protective metal housing. The assembly is designed tocarry fault current andto withstandthe magnetic forcesofsuch currents.

A cablebus is different from a metal-enclosed busin sev-eral important ways. Cablebus is more of a hybrid betweencable tray and busway. It uses insulated conductors in anenclosure that is similar to a cable tray with covers.Cablebus is normally furnished as components for field as-sembly, butcan be furnishedas factory-assembled sections.Cablebus is generally not subject to expansion or contrac-tion problems. The enclosure is normally manufacturedfrom aluminum or steel and resembles a cable tray withventilated bottom and top covers. The guide provides fur-ther details on types of cables, spacing, installation, etc.

Cable Installation (C lause 13)

Cable installation specifications and construction supervisionisoften neglected incommonindustry practice. Yet, cable in-stallation damage and improper terminations and splices arewidely cited as the most frequent cause of cable failures,hence, the decision to include this clause in the guide to pro-vide a summary of installation requirements and practicesalong with references to more detailed specifications.68

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Therearevarious considerationswheninstalling electri-calcables. Cables installedundergroundmay bedirectbur-ied or pulled into underground conduit. Fig. 9 illustratesthe use of rollers to minimize bend damage when pullingcable through manholes. Cables above ground may be in-stalled in conduit, cable tray, or on an aerial messengerwire. Fordetails on types of installations andother installa-tion criteria, refer to IEEE 576-2000.

Conclusion

This guide is subject to reaffirmation or change after fiveyears from publication. Thus, a new WG has been orga-nized to undertake an update and expand the originalguide. It is hoped that users will provide feedback so thatimprovements can be incorporated in the next issue. Atthat time, theWGmaywant to include some InternationalElectrotechnical Commission standards and informationon cables made to such standards. These types of cables arebeingused inpetroleumand chemical plantsin many othercountries. Also, cables associated with fixed and floatingoffshore oil facilities should be considered, although thesetypes of cable are included in other standards. Those inter-ested in the contents of this guide, or other cable-relatedtopics, including the proposed topics covered above,should give consideration to joining this WG, which hasnowbeen reactivated under PCIC sponsorship with a com-panion WG in the PES/ICC organization.

AcknowledgementsThe authors wish to thank all present and past members ofthe P1242 WGand othersfromboth the PCICand the ICCfor their dedication and service to this project. We wish toespecially thank and recognize the major clause editors asfollows: Sunita Kulkarni (Clause 3), L. Bruce McClung(Clause 4), David C. Mercier (Clause 5), William D.Wilkens (Clause 6), Craig M. Wellman (Clause 7), Carl C.

Landinger (Clause 8), Kenneth E. Bow (Clause 9), H.R.Stewart (Clause 10), Douglas E. Effenberger (Clause 11),Justo Benitez (Clause 12), and Bill Taylor (Clause 13).

The authors also wish to thank Yvette Ho Sang, ourIEEE Project Editor, and Bruce Barrow, Chairman of SSC10, for their help and contributions toward the successfulcompletion of this guide.

References[1] M.G. Bayer, K.E. Bow, J.H. Snow, D.A Voltz, Wire and cable up-

date1990, IEEE Trans. Ind. Applicat., vol. 28, pt. 1, pp. 211-220,

Jan.-Feb. 1992.

Donald A. Voltz ([email protected]) is with MustangEngineering, L.P. in Houston, Texas, USA. Joseph H. Snow iswith Anixter Inc. in Angleton, Texas, USA. Snow is a LifeMember of the IEEE, and Voltz is a Member of the IEEE. Thisarticle first appeared in its original form at the 2000 IEEE/IASPetroleum and Chemical Technical Conference.

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Cables - Cable for Petrochemical Plants IEEESTANDARD1242