MC Single Conductor 2-Hour Fire Rated Cable Grounding

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whiggins

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I have a feeder from a fused disconnect (700A fuse) routed through a building to a fire pump controller. The feeder will consist of 3 single conductor, 2/0, MC 2-hour fire rated cables (VITALink) bundled together. Each cable has a copper sheath for grounding that is the equivalent of 1 AWG. Table 250.122 requires a 1/0 for grounding. VITALink sales told me in single conductor bundled applications that the 1 AWG is additive for the three cable sheaths.

I'm not able to find this additive feature in the NEC. Perhaps this is a UL listing thing?

Any insight would be appreciated.
 
From the NEC I think that this is as close as you'll get from Article 332. You're saying that the manufacturer says that it's adequate because of the combined area of the three cables? There is a provision in 250.122(A) for sectioned EGC's but that is within one cable.

III. Construction Specifications
332.104 Conductors. Type MI cable conductors shall be
of solid copper, nickel, or nickel-coated copper with a re-
sistance corresponding to standard AWG and kcmil sizes.
332.108 Equipment Grounding Conductor. Where the
outer sheath is made of copper, it shall provide an adequate
path to serve as an equipment grounding conductor. Where
the outer sheath is made of steel, a separate equipment
grounding conductor shall be provided.
Click to expand...
 
david luchini said:
T250.122 required a 1/0 for a "wire type" egc. You don't have a wire type egc, you don't need to meet T250.122.
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Good point, I wonder who is saying that the copper jacket is actually equivalent to a #1 AWG conductor? For the jacket it would need to comply with 250.4(A)(5) or similarly (B)(4).

250.122 Size of Equipment Grounding Conductors.
(A) General. Copper, aluminum, or copper-clad aluminum
equipment grounding conductors of the wire type shall not
be smaller than shown in Table 250.122, but in no case
shall they be required to be larger than the circuit conduc-
tors supplying the equipment. Where a cable tray, a race-
way, or a cable armor or sheath is used as the equipment
grounding conductor, as provided in 250.118 and
250.134(A), it shall comply with 250.4(A)(5) or (B)(4).
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250.4(A)(5) Effective Ground-Fault Current Path. Electrical
equipment and wiring and other electrically conductive ma-
terial likely to become energized shall be installed in a
manner that creates a low-impedance circuit facilitating the
operation of the overcurrent device or ground detector for
high-impedance grounded systems. It shall be capable of
safely carrying the maximum ground-fault current likely to
be imposed on it from any point on the wiring system
where a ground fault may occur to the electrical supply
source. The earth shall not be considered as an effective
ground-fault current path.
Click to expand...
 
Thank you guys for great responses.

I don't think they test their cables for ground current capability, they just figure up the equivalent area of the copper jacket and relate it to T250.122. The manufacturer publishes this data in table form. I suppose that is an easy way to relate it and probably avoid some testing.

Reading 250.4(A)(5) seems to leave open adding them together.
 
whiggins said:
Thank you guys for great responses.

I don't think they test their cables for ground current capability, they just figure up the equivalent area of the copper jacket and relate it to T250.122. The manufacturer publishes this data in table form. I suppose that is an easy way to relate it and probably avoid some testing.

Reading 250.4(A)(5) seems to leave open adding them together.
Click to expand...

I would accept the manufacturer's opinion that the three cable jackets in concert meets the requirement of 250.4(A)(5).
 
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