Supplementary Equipment Grounding Conductor - code requirements

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ClintonE

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NEC 250.96(A) mentions the use of "supplementary equipment grounding conductors." Is there anywhere in the code that identifies the requirements of a supplementary EGC?

Background: There is an existing 400A feeder ran in a 4" EMT with set screw fittings, there is no wire EGC. The engineers at our company do not consider this to be a good practice and we normally provide a wire EGC for each feeder. Is there any way to provide a supplementary wire EGC without having to re-pull the existing feeder? Can a "supplementary" EGC be provided outside the 4"C, or in a different conduit, or would NEC 300.3(B) prevent this?
 
There is no such thing as a supplementary EGC. If you need one of the wire type, it must be installed in the raceway with the feeder conductors. 300.3(B) does prohibit this, and there are no other provisions in the code that I am aware of that would permit the EGC to be run outside the feeder raceway. Part of the issue the the inductive reactance that acts to limit the current flow on the EGC when it is not in the same raceway, especially a ferrous raceway.

This needs to be addressed in your project specifications, because, as you said, the raceway is. according to code, the required and effective ground fault clearing path.
 
If you have two separate raceways, with two separate circuits, following two separate paths to the same junction box, then the two separate EGCs would be required to be connected.

This tells me that if you have one raceway which the NEC considers an acceptable EGC, and you wish to run a separate wire EGC outside of the raceway, there is nothing that would prohibit this additional bit of bonded metal. This separate 'EGC' could not count as the required EGC for the circuit (as Don notes, that must be run inside the raceway or must be the raceway itself).

So I think you could have the raceway as the NEC required EGC and a separate bit of wire as the additional bonding that makes your company engineers happy. This additional bit of wire may need to be large enough for reasons of mechanical protection, or might be run in a separate raceway entirely.

Jon
 
For the OP, In 250.96(A) the term "supplementary" EGCs refers to when you have a metallic raceway system but choose to also also use a wire type EGC in the same raceway. It must be inside the raceway of the raceway in question.
 
winnie said:
If you have two separate raceways, with two separate circuits, following two separate paths to the same junction box, then the two separate EGCs would be required to be connected.

This tells me that if you have one raceway which the NEC considers an acceptable EGC, and you wish to run a separate wire EGC outside of the raceway, there is nothing that would prohibit this additional bit of bonded metal. This separate 'EGC' could not count as the required EGC for the circuit (as Don notes, that must be run inside the raceway or must be the raceway itself).

So I think you could have the raceway as the NEC required EGC and a separate bit of wire as the additional bonding that makes your company engineers happy. This additional bit of wire may need to be large enough for reasons of mechanical protection, or might be run in a separate raceway entirely.

Jon
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Where can I find this in the code? I got to thinking about this today, as I have always thought as long as the largest of EGC of the circuit conductors was bonded to the box it was good. But I’ve clearly been mistaken.
 
I agree with Jon. The installation is compliant as it stands. You can run another green wire just about anywhere you want to make those engineers happy. It’s just not an EGC per NEC.
 
ClintonE said:
NEC 250.96(A) mentions the use of "supplementary equipment grounding conductors." Is there anywhere in the code that identifies the requirements of a supplementary EGC?

Background: There is an existing 400A feeder ran in a 4" EMT with set screw fittings, there is no wire EGC. The engineers at our company do not consider this to be a good practice and we normally provide a wire EGC for each feeder. Is there any way to provide a supplementary wire EGC without having to re-pull the existing feeder? Can a "supplementary" EGC be provided outside the 4"C, or in a different conduit, or would NEC 300.3(B) prevent this?
Click to expand...
If you want it to be the EGC, then it must be in the raceway as pointed out per 300.3(B).
If you want it to be some other reference conductor, such as those that get installed for telecommunications facilities or other, then you can size it and run it however you want, but it cannot be identified as an EGC.
 
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