Class II Div II Hazardous EnvironmentOccupancy Sensor

Project SpecificationsFirst Edition

10/23/2012

Joint ECE (Team 166) and ME (Team 26) Senior DesignECE 4901/ME 4972

Fall 2012

AdvisorsSung Yeul Park (EE), George Lykotrafitis (ME)

Sponsored By:

Contact: David Behnke (Dave.Behnke@AcuityBrands.com)

Computer EngineeringChristopher Zannoni

Electrical EngineeringChristopher Zannoni

Joanne HitchcockGledi Progonati

Engineering PhysicsRussell Gee

Mechanical EngineeringMichael Gazda

James Fisher

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IntroductionProject Purpose

Used appropriately, occupancy sensors save electricity, extend component lifetime, provide a safer working environment, and ultimately provide extensive cost savings. Sensor Switch uses infrared sensing technology to build industry leading occupancy sensors that can be used in a multitude of commercial, residential and industrial environments. However, special considerations must be made in environments in which hazardous conditions exist. In an effort to create safer working conditions and minimize damaging accidents, the Occupational Safety and Health Administration (OSHA) has classified potentially dangerous environments according to the potential threat of explosions due to atmospheric gas and dust. Without proper safety precautions, electrical devices, including equipment such as occupancy sensors, can ignite an explosion that pose a serious threat to not just equipment, but human life as well. Our goal is to design an occupancy sensor that can operate in a hazardous Class II Division 2 environment.

Project DescriptionAn occupancy sensor, originally designed by Sensor Switch, will be modified to operate

safely in a Class II Division 2 hazardous environment. Such an environment is defined by the National Electric code (NEC) as having the potential for explosive dust clouds being created due to mishandling or accidents. Also it should be noted that the IEC hazardous area classification of Zone 22 matches the previous requirement, however this was not mentioned by the sponsor we should be aware of this classification. Zone 22 is defined as a place in which an explosive atmosphere, in the form of a cloud of combustible dust in air, is not likely to occur in normal operation but, if it does occur, will persist for a short period only. For example, leaks from incorrectly fitted lids or spillages.

The relay shall be protected from the environment in some manor, isolating the potentially explosive switch from the dust source. Furthermore, the occupancy sensor itself will be analyzed and potentially modified to assure the electronics are inherently safe. Last, the occupancy sensor must be able to communicate with the relay, either wirelessly or by a direct connection.

Cost Specifications and LimitationsSensor switch place a cost limitation on the project. They indicated the total cost of the

device[product sale price and product installation cost] must be low enough such that it would cost the consumer less to purchase this device than the savings realized due to a decrease in energy consumption over the course of three years using the device. The calculation for this value is as follows:

The supplied Sensor Switch CM 10 occupancy sensor can cover, on average, about 2400 square feet1, with fluorescent light fixtures on average consuming about 1 watt per square foot2 we can calculate that one sensor controls 2.4 kW worth of lights. With the average US cost per kWh of $0.10/kWh in 20123 and using a figure of 3000 hours/year a facility operates4 one occupancy sensor controls $720/year worth of electricity. Storage areas or warehouses would be 1 http :// www . sensorswitch . com / OnlineCatalog . aspx ? sn = cm %2010 2 http :// www . gelighting . com / LightingWeb / na / resources / tools / lighting - assistant - toolkit / lighting - layout - estimator . jsp 3 http :// www . eia . gov / electricity / monthly / pdf / epm . pdf 4 57hours/week from: http://infohouse.p2ric.org/ref/32/31316.pdf

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a good example a division 2 area5. According to a U.S. EPA Prediction6 a storage area is occupied 45%-80% of the time. Using this percentage, one sensor would save $144-$396 per year in electricity costs if the lights were on 100% of the operating time without a sensor. Using the 3 year constraint mentioned earlier the cost of the sensor, relay and installation, cannot be more than $432-$1188.

Regulations Related to Project that Drive Specifications:The largest part of our project specifications come from hazardous location regulations.

Below are the specifications from various hazardous location regulations that pertain to our project

NEC 2011 Regulations:

Article 500: Hazardous (Classified) Locations, Classes I, II, III, Divisions 1 and 2

500.5 Classifications of LocationsClass II, Division 2.

A Class II, Division 2 location is a location: Where combustible dust may be present in the air in quantities that can produce

explosive or ignitable mixtures Where combustible dust accumulations are present but there is not enough dust to

interfere with the operation of electrical equipment, but it could interfere with operation of equipment if there is mishandling of equipment and the dust becomes suspended in the air.

Where combustible dust accumulates near electrical equipment it can interfere with the safe dissipation of heat from electrical equipment, or there could be an ignitable failure of electrical equipment.

500.6 Material GroupsClass II Group Classifications

Group E. Atmospheres containing combustible metal dusts, including aluminum, magnesium, and their commercial alloys, or other combustible dusts whose

5 Understanding Hazardous Area Sensing-Intrinsic Safety, handbook by Bob Svacina and Brad Larson found at: http://www.parrinst.com/wp-content/uploads/downloads/2011/06/Svacina-Larson_Understanding-Hazardous-Area-Sensing_Intrinsic-Safety.pdf6 Although the actual report could not be found, this number is used throughout the industry. Additionally we did find a study by a member of the EPA ENERGY STAR Buildings Program, Bill VonNeida, who referenced that this number. The report is found here: http://www.lrc.rpi.edu/resources/pdf/dorene1.pdf

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particle size, roughness, and conductivity present hazards in the use of electrical equipment (resistivity <100 kΩ/cm).

Group F. Atmospheres containing combustible carbonaceous dusts. Coal, carbon black, charcoal, and coke dusts are examples of carbonaceous dusts (100 kΩ/cm < resistivity <100 MΩ/cm).

Group G. Atmospheres containing combustible dusts not included in Group E or F, including flour, grain, wood, plastic, and chemicals (resistivity >100 kΩ/cm).

The explosion characteristics of air mixtures of dust vary with the materials involved. For Class II locations, Groups E, F, and G, the classification involves the tightness of the joints of assembly and shaft openings to prevent the entrance of dust in the dust- ignition proof enclosure. If dust enters and accumulates, the layers of dust on the equipment may cause overheating.

Certain dusts may require additional precautions due to chemical phenomena that can result in the generation of ignitable gases.

Here is a table of all combustible materials and their NEC groups as well as their layer/cloud ignition temperature

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Low Ignition Temp. Class II,

Div. 2, Groups E, F, &G Combustible Dusts

Group Ignition Temp. (C)

Sevin G 140

Ferbam G 150

Violet 200 Dye G 175

Soy Flour G 190

Sulfur G 220

500.7 Protection Techniques Dust Ignitionproof. This protection technique shall be permitted for equipment in Class

II, Division 1 or 2 locations.As defined by Article 502-1 of the NEC:“The apparatus is enclosed in a manner that will exclude ignitable amounts of dusts and will not permit arcs, sparks or heat generated or liberated inside the enclosures to causeIgnition of exterior dust accumulations on the enclosure or of atmospheric dust suspensions in the vicinity of the enclosure.”

Dusttight. This protection technique shall be permitted for equipment in Class II, Division 2 or Class III, Division 1 or 2 locations.

Nonincendive Circuit. This protection technique shall be permitted for equipment in Class I, Division 2; Class II, Division 2; or Class III, Division 1 or 2 locations.

The energy stored and produced by the circuit is less than the ignition values of the charts given below

Nonincendive Equipment. This protection technique shall be permitted for equipment in Class I, Division 2; Class II, Division 2; or Class III, Division 1 or 2 locations.

The energy producing equipment has to produce and store less enrgy than the ignition values of the charts given below

Nonincendive Component. This protection technique shall be permitted for equipment in Class I, Division 2; Class II, Division 2; or Class III, Division 1 or 2 locations.

The energy producing components has to produce and store less energy than the ignition values of the charts given below

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Hermetically Sealed. This protection technique shall be permitted for equipment in Class I, Division 2; Class II, Division 2; or Class III, Division 1 or 2 locations.

An enclosure that is sealed air tight and certified to be used in a hazardous location

500.8 Construction and installation of equipment under hazardous locations Suitability of equipment

o All equipment must have a listing or label with evidence from a qualified testing laboratory or inspection agency concerned with product evaluation

Approval for Class and propertieso All equipment shall be identified not only for the class of location but also for all

of the explosive, combustible, or ignitable properties of the specific gas, vapor, dust or fibers/flying that will be present. Class II equipment shall not have an external temperature higher than the ignition temperature of the specific dust to be encountered see figure below

Max Temp touching environment

There are subcategories of allowed temperature dependent on the type of dust encountered in the environment, as demonstrated in the table below. To satisfy all categories, temperature must be below 85° C.

If the apparatus is tested and certified to be identified to be used in a Division 1 location, this apparatus shall be permitted in a Division 2 location

Marking

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o All equipment shall be marked to show the environment for which it has been evaluated.

Class Division Materials (Groups E, F, and G) Equipment Temperature: the operating temperature and the maximum safe

operating temperature Threading: The supply connection entry thread form shall be NPT or metric. Conduit and

fittings shall be made wrench tight to prevent sparking when fault current flows through the conduit system, and to ensure the explosion proof integrity of the conduit system where applicable. Equipment provided with threaded entries for field wiring connections shall be installed in accordance with the following: Equipment Provided with Threaded Entries for NPT Threaded Conduit or Fittings. For equipment provided with threaded entries for NPT threaded conduit or fittings, listed conduit, conduit fittings, or cable fittings shall be used. All NPT threaded conduit and fittings shall be threaded with a National (American) Standard Pipe Taper (NPT) thread. Unused Openings: All unused openings shall be closed with listed metal close-up plugs. The plug engagement shall comply with the above.

Article 502: Class II Locations502.5 Explosionproof Equipment

Explosion proof equipment and wiring shall not be required and shall not be acceptable in Class II locations unless also indentified for such locations.

Note: Electrical equipment required in Class II locations is different from that required for Class I locations. Class II equipment is designed to prevent the ignition of layers of dust, which may cause an increase in operating temperature, which Class II equipment does not address this concern.

Dust-ignition proof enclosures are not required to be explosion proof502.6 Zone Equipment

Equipment listed and marked in accordance with 506.9(c) for Zone 20,21,22 locations shall be permitted in Class II div 2 locations for the same dust atmosphere and with a suitable temperature class.

II. Wiring502.10 Wiring Methods

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1. Rigid metal conduit, intermediate metal conduit, electrical metallic tubing, dusttight wireways

2. Type MC or MI cable with listed termination fittings3. Type PLTC and Type PLTC-ER cable in accordance with the provisions of article 725,

including installation in cable tray systems. The cable shall be terminated with listed fittings

4. Type ITC and Type ITC-ER cable as permitted in 727.4 and terminated with listed fittings.

5. Type MC, MI, or TC cable installed in ladder, ventilated trough, or ventilated channel cable trays in a single layer, with a space not less than the larger cable diameter between the two adjacent cables, shall be the wiring method employed.

6. Reinforced Thermosetting resin conduit RTRC, all marked with suffice –XW and Schedule 80 PVC conduit, shall be permitted

7. Exception Type MC cable shall be permitted to be installed without the spacing required by 5.

Flexable Connections.1. Dust tight flexible connectors2. Liquidtight flexible metal conduit with listed fittings3. Liquidtight flexible nonmetallic conduit with listed fittings4. Interlocked armor tyoe MC cable having an overall jacket of suitable polymeric material

and provided with termination fittings listed for class II, division 1 locations5. Flexible cord listed for extra-hard usage and terminated with listed dusttight fittings,

Where flexible cords are used they shall comply with 502.1401. Liquidtight flexible conduit or extra-hard-usage flexible cord is permitted.

However a bonding jumper must be provided around such conduit (see 502.30), and an additional conductor for grounding must be used in conjunction with flexible cords.

Nonincendive field wiring: (wiring entering or leaving an enclosure where grounding or shorting of the wiring does not ignite the atmosphere around it)Installation:

1. In separate cables2. In multiconductor cables where the conductors of each circuit are within a grounded

metal shield3. In multiconductor cables or in raceways where the conductors of each circuit have

insulation with a minimum thickness of 0.25mm.All boxes and fittings shall be dusttight

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502.15 Sealing, Class II, Divisions 1 and 2Raceway connection between a dust-ignition proof enclosure and one that is not:

1. A permanent and effective seal2. A horizontal raceway not less than 3.05m (10ft)long3. A vertical raceway not less than 1.5m(5ft) long and extending downward from the

dust-ignition proof enclosure4. A combination of 2 and 3

502.25 Uninsulated Exposed Parts, Class II, Divisions 1 and 2There shall be no uninsulated exposed parts that operate at more than 30 volts (15 for wet locations). These parts shall be protected according to sections 500.7(E), (F), and (G)

502.30 Grounding and Bonding, Class II, Divisions 1 and 2(A) Bonding

Bonding jumpers need to be used when grounding, not locknuts(B) Types of Equipment Grounding Conductors

Liquidtight flexible metal conduit shall include and equipment bonding jumper of the wire type in compliance with 250.102Exception for Class II Div 2: Over current protection in the circuit is limited to 10 amps or less or The load is not a power utilization load

502.35 Surge Protection — Class II, Divisions 1 and 2Surge protectors shall be enclosed

III. Equipment

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502.100 Transformers and CapacitorsCan not contain liquid that will burn. If it does then it needs to be in a vaults that comply with 450.41-450.48

502.115 Switches, Circuit Breakers, Motor Controllers, and Fuses(B) Class II, Division 2. In Class II, Division 2 locations, enclosures for fuses, switches, circuit breakers, and motor controllers, including push buttons, relays, and similar devices, shall be dusttight or otherwise identified for the location.

502.120 Control Transformers and ResistorsSwitching mechanisms and coils/ windings have to be dusttight

502.140 Flexible Cords — Class II, Divisions 1 and 2 Be supported by clamps so there is no tension on the wires Must be dusttight

502.145 Receptacles and Attachment Plugs Of the type that provides for connection to the equipment grounding conductor of the

flexible cord and shall be designed so that connection to the supply circuit cannot be made or broken while live parts are exposed

The following information summarizes section 504 of the National Electrical Code. The abbreviation IS will be used to abbreviate “Intrinsically Safe”. Sections of particular relevance to our project have been bolded.

Article 504: Intrinsically Safe ConductorsDefinition: “Simple Apparatus”:

A. Passive Components (switches, junction boxes, resistors, simple semiconductors (i.e. LEDs)

B. Sources of stored energy consisting of single components (i.e. capacitors or inductors)C. Sources of generated energy (i.e. photocells)

Control DrawingsA. IS apparatus, associated apparatus and other equipment shall be installed in accordance

with the control drawing(s).i) Control drawing identification is marked on apparatusii) Associated apparatus over 250 V has special conditions

Since IS systems are to be installed according to control drawing, this puts limitations on cables and separation of circuits in the system. Also illustrates what is allowed to be connected to system. Testing by third parties is based on installation with accordance with control drawing.Surface Temperature

Surface Temp can be calculated by following equation:

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T=P0Rth+Tamb

P0 = output powerRth = thermal resistance of simple apparatusTamb = ambient temperature (typically room temp, but also reference Table 500.8)In addition, components with surface area less than 10cm2 may be classified as T5 if surface temperature does not exceed 150C.

Wiring methods suitable for unclassified locations (covered Ch7, Ch8) are permitted for IS. Separation of IS Conductors

a) Conductors of IS circuits cannot be placed in raceways, cable tray or cable with conductor from non-IS circuiti) Exception: If conductors are separated by 50mm and secured or by an approved

insulating partition or grounded metal partitionii) Exception: All IS conductors and all non-IS conductors are in grounded metal-

sheathed or metal-clad cables where fault current is capable of going to groundiii) Exception: IS circuit in Div2 or Zone 2 shall be permitted to be installed in a

raceway, cable tray or cable along with nonincendive field wiring circuits when installed as long as :1. Conductors are within a grounded metal shield OR2. Conductors of each circuit have insulation with min thickness of .25mm

b) In enclosures, conductors of IS circuits shall be secured so that any conductor that might come loose from a terminal in unlikely to come into contact with another terminal. One of the following methods may be used to do this:i) Separation by at least 50mmii) Separation by grounded metal partition or insulated partitioniii) Metal sheathed cables

Groundinga) IS apparatus, enclosures and raceways shall be connected to equipment grounding

conductorb) Associated apparatus and cable shields must be grounded with accord to control drawingc) When connection to grounding electrode is necessary, special conditions necessary (see

NEC for details)Bonding

a) Hazardous Locations: IS apparatus shall be bonded with accordance to 250.100. 250.10 summarized as follows:

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i) Ground clamps and other fittings are approved for general use without protection if they are in installations where they are unlikely to be damaged, or enclosed in metal, wood or equivalent protective covering.

b) Unclassified: See NECSealing

a) Conduits and cables required to be sealed by NEC shall be sealed to minimize passage of hazardous gases, vapors, dusts. Such seals shall not be required to be explosionproof or flameproof but shall be identified for the purpose of minimizing dust passage under normal operating conditions and shall be accessible.

b) Exception: Seals shall not be required for enclosures that contain only IS safe apparatus, except as required by 501.12(F)(3)

Identificationa) Terminals: IS circuits shall be identified at terminal and junction locations in a manner

intended to prevent unintentional interference with the circuits during testing and servicing.

b) Wiring: Raceways, cable trays and other wiring methods for IS system wiring shall be identified with the affixed label: “Intrinsic Safety Wiring” or equivalent. Must be visible after installation and placed to be readily traced through entire length of installation. Labels shall be appear in every section separated by enclosures, walls, partitions, floors. Spacing between labels cannot exceed more than 7.5m. (Exception for underground cables).

c) Color Coding: Color coding shall be permitted to identify IS conductors colored light blue and where no other conductors colored light blue are used. (Basically if IS conductor is colored light blue, this satisfies Identification requirement as long as there are no other light blue conductors).

UL913, Fourth Edition, Regulations: Intrinsically Safe Apparatus 7

(2) Intrinsic Safe Apparatus

(2.1.1) The energy available in the hazardous location shall not be capable of igniting the flammable mixture specified in 8.3.1 through 8.3.5 due to arcing or hot surfaces during normal operation.

(2.1.1.1) Normal Operation is defined as:

7 From UL913, Fourth Edition from 1988. Due to cost constraint as of 10/23/12 the most recent edition, seventh edition from 2011, was not investigated. However the latest edition will be bought and investigated later in the project

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Circuit is at 1.5x its max energy rating

Environmental conditions within the ratings given:

Maximum rated supply voltage

Tolerances of components are at most unfavorable conditions

Adjustments are at most unfavorable

Shorting, grounding or opening of any field wires

(2.1.2.1)Circuit is under fault conditions, which include: (see article 2 for fault definitions)

The most unfavorable single fault and any subsequent related defects and breakdowns, with an additional test factor of 1.5 applied to energy;

The most unfavorable combination of two faults and any subsequent related defects and breakdowns, with no additional test factor. Such test factors are to be achieved according to the procedures outlined in 8.6 through 8.6.4.

(2.2.3) The possibility of arc ignition under normal and fault conditions is to be determined by either of the following two procedures:

Testing the circuit according to the test requirements of Section 8; or

Comparing the calculated or measured values of current, voltage, and associated inductances and capacitances to the appropriate figures in Section 5 to establish that the current and voltage levels are below the specified values in 5.2.1 through 5.2.2.

(2.2.4) Ignition sources are the following:

Sources of spark ignition:

Discharge of a capacitive circuit;

Interruption of an inductive circuit;

Intermittent making and breaking of a resistive circuit;

Hot wire fusing.

Sources of thermal ignition:

Heating of small gage wire strand;

Glowing of a filament;

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High surface temperature of components.

(2.4) Associated Apparatus Evaluation.

Associated apparatus is to be evaluated to determine that the output is intrinsically safe. Associated apparatus shall comply with 2.1 through 2.2.4.

(2.4.1) The maximum output voltage is to be the highest output voltage from the following:

No faults and the most unfavorable normal operating condition.

The most unfavorable one fault condition.

The most unfavorable two fault condition.

(2.4.2) The maximum output current is to be the highest shortcircuit current obtainable under the conditions specified in 2.4.1.

(2.4.3) The maximum allowed capacitance is determined by test or by comparison and is the lower value obtained from the following:

The maximum capacitance that does not cause ignition at 1.22 times the maximum output voltage if this voltage was determined with less than two faults.

The maximum capacitance that does not cause ignition at the maximum output voltage if this voltage was determined with two faults.

(2.4.4) The maximum allowed inductance is determined by test or by comparison and is the lower value obtained from the following:

The maximum inductance that does not cause ignition at 1.22 times the maximum output current if this current was determined with less than two faults.

The maximum inductance that does not cause ignition at the maximum output current if this current was determined with two faults.

(2.5) Intrinsically Safe Apparatus Inductance and Capacitance Determination. The intrinsically safe apparatus maximum internal capacitance or inductance is to be determined considering both normal and fault conditions by one of the following methods:

Inspection or analytical computation; or

Confirmation of the value by testing in accordance with 7.14.1 through 7.14.6, if the apparatus manufacturer declares a maximum internal capacitance or maximum internal inductance value; or

Derivation of the value of maximum internal capacitance or maximum internal inductance using the procedure specified in 7.14.1 through 7.14.6.

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Faults:

Fault Definitions:

One fault is counted if all associated apparatus common to the loop are considered to be at their maximum voltages and currents.

A fault is only counted after 2 shorts of the outputs or after 1 grounded output. If two associated apparatus outputs are shorted and then the connection is grounded, the grounding is a countable fault.

Current limiting resisters are not considered subject to fault if are a film type, wirewound type, or if broken provide a larger resistance

Shunt protective components are not considered subject to fault (see section for details)

(2.6) Intrinsically Safe and Associated ApparatusA control drawing needs to accompany the part shall contain notes to explain the following if applicable:

Specifies the allowed apparatus on each terminal

Which apparatus terminal normally supplies power

(2.6.7)Polarity for associated apparatus

(2.6.7)How to calculate allowed capacitance and inductance values for field wiring used in the intrinsically safe circuit

(2.7) Intrinsically Safe Apparatus Evaluation. Intrinsically safe apparatus is to be evaluated for the possibility of arc ignition or hot surface ignition using 2.1 through 2.2.4. The associated apparatus connected to each terminal is determined from the control drawing. The number of faults counted when connecting various allowed combinations of the associated apparatus is described in 2.6 through 2.6.7.

(2.7.1)The determination of temperature rise of a component in an entity evaluation is to be made using a power source having parameters that are within the stated entity parameters at a voltage and current that is on the relevant ignition curve and that results in maximum power transfer.

(2.7.2)Capacitive discharge evaluation of the intrinsically safe apparatus is done using the highest specified maximum output voltage from any set of parameters adjusted by the test factor described in 2.1.2.1, considering current drawn from the source during discharge.

(2.7.3) Inductive discharge evaluation of the intrinsically safe apparatus is to be done using an equivalent power source that has parameters within the stated entity parameters at a voltage and current that lie on the relevant ignition curve. The source is to be chosen that causes

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maximum current flow in the inductor. The current is adjusted using the test factor described in 2.1.2.1.

(3)Construction Requirements

(3.1)Creepage and Clearance Distances (see table 1)

(3.1.1)If insulators are at least 1/3 of table values then they are considered a possible fault

(3.1.2)If separation is less than 1/3 of table values then they are considered a possible fault

(3.1.3) If more than two conductors are involved and the spacing between adjacent conductors is less than one third the applicable value in Table 1, the sum of the individual spacings is to be added until the total spacing equals or exceeds one third the applicable value. Only that number of conductors is to be considered connected. A single fault is to be counted. Within a total dimension equal to the applicable table value, only one such group of conductors is to be considered connected.

(3.4)If components are not rigidly supported so they don’t comply with table follow 3.4.1-3.4.3 for insulating and separating these components

(3.1.5)Printed circuits distance from ground planes to other traces don’t have to comply with table as long as they ground can carry max current at fault condition.

(3.1.6)Field wiring must be separated by 0.25in unless no hazard results from connection.

(3.1.7)Creepage under coating for PCB’s is:

1) Two layers of solder resist or varnish with min dielectric voltage rating of 200 volts per 0.025mm; or

2) A single layer of .7mm; or

3) Complies with voltage test in 7.7.3.

(3.2)Encapsulation

Can be used to separate conductors (casting compound table 1) if encapsulation is used to reduce ignition the minimum thickness has to be

(3.3)Field wiring

Adjacent terminals between IS an non-IS must be at least 50mm(2in). Care must be taken so that they do not come in contact with each other if dislodged.

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Plugs cannot be interchangeable as to prevent wrong connections.

(3.6)Miscellaneous Components

(3.6.1.1) Plugs shall not be interchangeable with non identical boards or components in the same apparatus.

Exception is if IS is not affected from interchange, if it is unlikely are identified so that it is unlikely

(3.7) Portable Apparatus Enclosures

(3.7.1)Exposed external surfaces of the external enclosure and parts shall be made of a nonsparking material, such as plastic or brass, unless the part is protected by a recess or a guard.

Exception: Such a surface may be of a sparking material if an investigation indicates that percussion sparks capable of igniting a flammable atmosphere are unlikely.

Nominal Voltage (V) 10 30 60 90Creepage Distance (mm) 1.5 2 3 4

Creepage Distance Under Coating (mm) 0.5 0.7 1 1.3Minimum Comparative Tracking Index 90 90 90 90

Clearance 1.5 2 3 4Distance Through Casting Compound 0.5 0.7 1 1.3

Distance Through Solid Insulation 0.5 0.5 0.5 0.7Table 1: “Clearances, Creepage Distances, and Distances Through Casting Compound and

Insulations”

(4.1) Max temperature

(4.1.1) If wiring other than wound coils or transformer wiring of intrinsically safe apparatus is copper and its current is in accordance with the requirements in Table 2, or the following equation, temperature tests to determine its maximum surface temperature are not

I−√ I m2 t [1+.00393 (T−t ) ]

TIn which:I is current and amperesIM is the current at which wire melts, amperesT is the temperature at which copper melts, 1083 Ct is the maximum acceptable wire temperature, C

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(4.2) Marking

The minimum marking shall include the following

(1)Identification of the apparatus, including manufacturers’ name or trademark and type or model designation.

(2)Hazardous location class and group.

(3)Max surface temp or temp number based of an ambient temp of 40°C (see Table 500-2(b) of NFPA 70-1987, National Electrical Code) Exception: Apparatus having a maximum surface temperature no greater than 100 ° C.

(4) For shunt diode and similar protective barrier assemblies which are intended for field or panel installation, the maximum nonhazardous location voltage. (See3.5.6.1.).

(5) Control drawing number, except for apparatus not intended to be connected to other apparatus or circuits.

(4.2.2) In addition to the minimum marking specified in 4.2.1, the marking shall include the following. As much information as possible shall be provided on the apparatus label. It is recognized, however, that it is impractical to mark small pieces of apparatus with all the

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required information. If this information is not on the apparatus, it shall be included in the accompanying literature.

(1) For intrinsically safe apparatus:

(a) An indication that the apparatus is intrinsically safe;

(b) If investigated using the entity evaluation, the maximum input voltage, maximum input current, maximum internal capacitance and maximum internal inductance;

(c) If repair is possible, a warning label worded "Warning - Substitution of Components May Impair Intrinsic Safety;" and

(d) A reference to accompanying literature, that provides special installation, maintenance, or operating instructions. If this information is not on the apparatus, it shall be included or referenced on the control drawing.

(2) For associated apparatus:

(a) If investigated using the entity evaluation, the maximum output voltage, maximum output current, maximum allowed capacitance, and maximum allowed inductance;

(b) If repair is possible, a warning worded "Warning - Substitution of Components May Impair Intrinsic Safety;"

(c) Any other necessary information, in particular, an indication of any other type of protection and its characteristics; and

(d) A reference to accompanying literature, that provides special installation, maintenance, or operating instructions. If this information is not on the apparatus, it shall be included or referenced on the control drawing.

4.2.3 Terminals, terminal boxes, and plugs and receptacles for connection to intrinsically safe circuits shall be clearly identified and clearly distinguishable. If color only is used to comply with this requirement, the color shall be light blue.

Comparison Procedure for Determining Spark Ignition Capability

(5.1.3) [Resistive] Circuits

(a) These figures apply only to circuits having an output voltage-current plot that is a straight line drawn between open circuit voltage and short-circuit current.

(5.1.5) [Resistive-Capacitive] Circuits

(a) Refer to Fig. 7 and 8. These curves represent capacitor discharge only. They do not include the additional current which may be available from the associated apparatus.

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(5.2) Maximum Voltage and Current Levels

(5.2.1) The circuit conditions are to include all normal and fault conditions described in this standard, excluding the 1.5 test factor.

(5.2.2.1) For normal or single fault operation, the current shall not exceed 80 percent of the value determined from Figures 1 through 6. The voltage shall not exceed 80 percent of the value determined from Figures 7 and 8.

(5.2.2.2) For two fault condition, the current shall not exceed 90 percent of the value determined from Figures 1 through 6. The voltage shall not exceed 90 percent of the value determined from Figures 7 and 8.

(6) Apparatus for Class II and Class III Locations

(6.1) Applicability of Other Requirements in this Standard.(6.2.3) Except as specified in 6.2.4, intrinsically safe apparatus shall be enclosed in a dusttight enclosure that complies with the requirements in 6.3.1 through 6.3.1.2. The apparatus shall also comply with the spark ignition requirements for Class I locations as follows:

Hazardous Location Applicable Limits Class II, Groups E Class I, Group Dand G; Class III or Methane

(6.2.4) Intrinsically safe apparatus not enclosed in a dusttight enclosure complying with the requirements in 6.3.1 through 6.3.1.2 shall comply with the spark ignition requirements specified in 6.2.3. In this case, it is to be assumed that all spacings do not comply with the creepage and clearance distance requirements specified in 3.1 and that all connections between live or grounded parts and conductors are in the most unfavorable condition. The number of such connections is unlimited.

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Standard Regulations for Electrical Safety8:

In addition to the above specifications, more general installation and application specifications are as follows.

1. Insulation Integrity:Completed wiring installations shall be free from short circuits and from grounds other

than those required or permitted by this subpart.

2. Interrupting Rating:Equipment intended to interrupt current at fault levels shall have an interrupting rating

sufficient for the nominal circuit voltage and the current that is available at the line terminals of the equipment. Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage sufficient for the current that must be interrupted.

3. Circuit Impedance and Other Characteristics:The over current protective devices, the total impedance, the component short-circuit

current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit protective devices used to clear a fault to do so without the occurrence of extensive damage to the electrical components of the circuit. This fault shall be assumed to be either between two or more of the circuit conductors, or between any circuit conductor and the grounding conductor or enclosing metal raceway.

4. Internal Parts:Internal parts of electrical equipment, including busbars, wiring terminals, insulators, and

other surfaces, may not be damaged or contaminated by foreign materials such as paint, plaster, cleaners, abrasives, or corrosive residues.

5. Mounting Safety:Electric equipment shall be firmly secured to the surface on which it is mounted. Wooden

plugs driven into holes in masonry, concrete, plaster, or similar materials are not considered secure means of fastening electric equipment.

6. 600 Volts, Nominal, or Less (Space and Electric Equipment):Sufficient access and working space shall be provided and maintained about all electric

equipment to permit ready and safe operation and maintenance of such equipment. Working space for equipment likely to require examination, adjustment, servicing, or maintenance while energized shall comply with the following dimensions, except as required or permitted elsewhere in this subpart. Switchboards, panelboards, and distribution boards installed for the control of light and power circuits, and motor control centers shall be located in dedicated spaces and protected from damage.

Additional Requirements not specified above due to time constraint.8 http :// www . osha . gov / pls / oshaweb / owadisp . show _ document ? p _ table = STANDARDS & p _ id =9880

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1) Cables and cable fittings shall be designed following the regulations of UL 2225

2) Dust-tight and Dust-ignition proof equipment shall be designed following the regulations of ISA 12.12.01

3) Any portable electric equipment shall be designed following the regulations of ISA 12.12.03

4) Other regulations that may need to be considered are as follows:

a) ISA 61241-0: Electrical Apparatus For Use In Zone 20, Zone 21 And Zone 22 Hazardous (Classified) Locations – General Requirements

b) ISA 61241-1: Electrical Apparatus For Use In Zone 21 And Zone 22 Hazardous (Classified) Locations – Protection By Enclosures “ “TD”

c) ISA 61241-10: Electrical Apparatus For Use In Zone 20, Zone 21 And Zone 22 Hazardous (Classified) Locations – Classification Of Zone 20, Zone 21 And Zone 22 Hazardous (Classified) Locations.

d) ISA 61241-11: Electrical Apparatus For Use In Zone 20, Zone 21 And Zone 22 Hazardous (Classified) Locations – Protection By Intrinsic Safety “ID”

e) ISA RP12.06.01: Recommended Practice For Wiring Methods For Hazardous (Classified)Locations Instrumentation Part 1: Intrinsic Safety

f) The following specification might be needed to test the sensor that is assumed to be intrinsically safe: ISA TR12.2: Intrinsically Safe System Assessment Using The Entity Concept