Using a Shield for Equipment Grounding Conductor

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redtail_MH

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Where in the NEC does it permit a cable shield to be used for an equipment grounding condutor?

250.118 (9) states " The copper sheath of mineral-insulated, metal-sheathed cable."

This option seems to only apply to mineral-insulated cable, not metal-sheathed cables in general. Also, what is the difference between a sheath and shield (is it the same thing)?
 
I don't think you will find permission to do this. I assume that you are referring to the shield in a co-ax or similar cable. The code does state that, in general, the equipment grounding conductor must be run with the circuit conductors. The shield in a communicatios wire will not meet this criteria. You may be required to bond the shield to the equipment chassis, but that does not replace the equipment ground.
 
It is conceivable that in certain instances the sheath could be large enough to be considered a grounding conductor, but I wouldn't generally do it. Is your system a multi grounded system or a singly grounded one? What size is the phase wire?

The sheath must be capable of clearing a fault if used as a grounding conductor, and that would be suspect in all but soome of the smaller size wires. If you have a multi grounded system, the ground is the neutral and it must be at least 1/3 the size of the phase wire. Sheaths aren't always 1/3 the ampacity of the phase wire they enclose.

Jim T
 
haskindm said:
I don't think you will find permission to do this. I assume that you are referring to the shield in a co-ax or similar cable. The code does state that, in general, the equipment grounding conductor must be run with the circuit conductors. The shield in a communicatios wire will not meet this criteria. You may be required to bond the shield to the equipment chassis, but that does not replace the equipment ground.
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Sometimes it can. 820-41.
 
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