By Mike Holt, for EC&M Magazine
Imagine how terrible it would be if you were putting gas in
your company truck or your personal automobile, and the gas dispensing station erupted
into a ball of fire. A primary goal of Article 514 is to prevent just such a thing from
Note: Graphics are not contained in this newsletter.
A key question that arises in applying Article 514 is, What
is a motor fuel dispensing facility? We can see in 514.2 that its a location
where gasoline or other volatile flammable liquids or liquefied flammable gases are transferred
to the fuel tanks (including auxiliary fuel tanks) of self-propelled vehicles or approved
Classified or not?
Here are some rules to bear in mind when determining if a motor dispensing facility is classified or unclassified:
When you install electric equipment and wiring within a Class I, Division 1 or 2 location (as defined in Table 514.3(B)(1)), you must do so per the installation requirements contained in Chapters 1 through 4 of the NEC, plus the requirements contained in Articles 500 and 501. For this reason, you must use threaded Rigid Metal Conduit (RMC) or threaded Intermediate Metallic Conduit (IMC) for fixed wiring. But, if you are installing the wiring underground, you can use Rigid Nonmetallic Conduit (RNC) in accordance with 514.8.
[514.7] You must install wiring above a Class I, Division 1 or 2 location (as defined in Table 514.3(B)(1)) in a raceway or inside a cable that meets the requirements of 511.7(A)(1). See Figure 3 ec514-03 514-07.
[511.7(B)] If fixed lighting is over travel lanes (or where its exposed to physical damage), you must locate it not less than 12 ft above floor level, unless the luminaire is of the totally enclosed type or constructed to prevent sparks or hot metal particles from escaping.
[514.8] Electrical wiring underground below the surface of a Class I, Division 1 or 2 location (as defined in Table 514.3(B)(1)) is Class I, Division 1 to the point of emergence above grade. You must install underground wiring in threaded RMC or threaded IMC (See Figure 4 ec514-04 514-08). But, theres an exception to this. You can use RNC underground below a Class I, Division 1 or 2 location if the raceway is buried under not less than 2 ft of cover. Otherwise, you have to use threaded RMC or threaded IMC for the last 2 ft of the underground run to emergence, or to the point of connection to an aboveground raceway (See Figure 5 ec514-05 514-08x2).
[514.9] The raceway seal carries its own set of requirements, depending on the location:
(A) At the dispenser. You must install a listed raceway seal in each conduit run entering or leaving a dispenser. This seal has to be the first fitting after the conduit emerges from the earth or concrete (See Figure 6 ec514-06 514-09A).
(B) At the boundary. You must install a listed raceway seal in each conduit run that leaves a Class I, Division 1 or 2 location. [501.5(A)(4) or 501.5(B)(2)] You cant use any unions, couplings, boxes or fittings (except explosionproof reducers) between the seal fitting and the point where the conduit leaves the Class I area (See Figure 7 ec514-07 514-09B 01).
[501.5(C)] The raceway seal must be accessible, and cannot contain splices. The total conductor area cannot exceed 25 percent of the cross-sectional area of rigid metal conduit, unless the seal fitting is approved for 40 percent fill (See Figure 8 ec514-08 514-09B 02 501-05C6).
Disconnects and controls
[514.11 ] Disconnects for dispensing stations need to allow for rapid response to a hose breakage or other event that creates a fuel-related fire or explosion hazard:
(A) Each circuit leading to or through a dispenser (including equipment for remote pumping systems) must have a clearly identified and readily accessible switch (located remote from the dispenser) to disconnect simultaneously all conductors of the circuit (including the grounded neutral conductor). You cant use single-pole breakers with handle ties.
(B) Attended self-service stations must have the dispenser disconnect located no more than 100 ft from the dispenser, at a location acceptable to the AHJ.
(C) Unattended self-service stations must have the dispenser disconnect located more than 20 ft, but less than 100 ft, from the dispensers at a location acceptable to the AHJ. You must install additional emergency controls on each group of dispensers or the outdoor equipment used to control the dispensers to shut off all power to all dispensing equipment at the station.
[514.13] Remote pump control wiring for dispensers must be isolated to prevent electrical feedback. This means dispenser pump control wiring cannot supply more than one dispenser. Otherwise, it could cause electrical feedback when another dispenser is in operation (See Figure 9 ec514-09 514-13 cc514-02).
The goal of grounding is to eliminate the potential for current flow between metal objects or between metal objects and ground, and to prevent flashovers and arcing.
A key purpose of Article 514 is to prevent undesired or catastrophic ignition of flammable gases or liquids at fuel dispensing stations. When you follow the requirements of this Article, you are isolating ignition sources through proper sealing and preventing sparks through proper grounding. You are also providing for a safe, fast, and reliable means of interrupting power to the dispensing station if the unthinkable happens.
Copyright © 2002 Mike Holt Enterprises,Inc.