EGC equivalents for MC- Corrogated tube-type cable(C-L-X)

[Monty Elsom]

The situation: Parallel 480VAC 3 phase MC feeders, using 3/c w/gnd cable, industrial facility, not previously required by a state inspector to oversize the EGC to meet NEC 2008 250-122(F).
Art. 250-118(10) allows the use of the corrugated tube-type armor as an EGC. The cable manufacturer UL's the armor for use as an EGC but does not give it's equivalent AWG size. Can we assume that the armor equals the copper ground conductor AWG that is provided in the MC Cable and therefore use the total of the two to satisfy Art. 250-122(F)? Is there an exception by interpretation from AHJ's that allows installations to utilize the armor and installed ground conductor without having to provide a 4/c w/gnd MC cable to meet 250-122(F)?

 

[Dennis Alwon]

I have never heard of doing that as there is no way to calculate that the length of the equipment grounding conductor and the cable would be the same.

I am not familiar with the cable you mentioned but the only way to be compliant, IMO is to have a full size equipment grounding conductor unless the equipment grounding conductor in each one cable satisfies T250.122.

 

[don_resqcapt19]

If the cable armor is suitable for use as an EGC, there is nothing more you need to do. It is just like using metal conduit as the EGC, there is no requirement to do anything different when you run the conduits in parallel. The wording in 250.122(F) only applies to EGCs of the wire type.

 

[infinity]

Do you have a link to this type of cable where the armor is a listed EGC?

Welcome to the Forum.

 

[don_resqcapt19]

This Okonite document says the jacket is a code compliant EGC, but also says they provide an internal EGC of the wire type. The wire type equivalent size is shown on page 11, based on the OD of the cable.
I am not sure if anyone makes corrugated tube MC without an internal EGC of the wire type.

 

[electricalist]

If the wire type egc exist wouldnt he be obligated to use it,, the same way if you pull a ground in a metal raceway,,you cant say well the wire ground is too small then im using the pipe as my egc?

 

[don_resqcapt19]

If the wire type egc exist wouldnt he be obligated to use it,, the same way if you pull a ground in a metal raceway,,you cant say well the wire ground is too small then im using the pipe as my egc?

If the cable jacket or the conduit is an EGC there is no obligation to use the EGC of the wire type that is installed in the cable or raceway. If you do use the wire type EGC it must comply with the sizing rules in 250.122.

 

[electricalist]

Mr.Don you are unraveling all that I thought to be true.
If I have a conduit and I pull a ground wire in it I don't have to use it.
So let's say my conduit ends at a new disconnect and the ahj says my egc the wire type is too small, I can simply say no problem I'm using the conduit as the egc?

 

[ActionDave]

Mr.Don you are unraveling all that I thought to be true.
If I have a conduit and I pull a ground wire in it I don't have to use it.
So let's say my conduit ends at a new disconnect and the ahj says my egc the wire type is too small, I can simply say no problem I'm using the conduit as the egc?

As long as the wire isn't connected to anything it's not an EGC, it's just a wire.

 

[don_resqcapt19]

Mr.Don you are unraveling all that I thought to be true.
If I have a conduit and I pull a ground wire in it I don't have to use it.
So let's say my conduit ends at a new disconnect and the ahj says my egc the wire type is too small, I can simply say no problem I'm using the conduit as the egc?

I am not aware of any code section that he could cite to require you to use the wire type equipment grounding conductor, assuming that your raceway is suitable for use as an EGC.

 

[Monty Elsom]

EGC Equivalents for MC

EGC Equivalents for MC

Thank you all for your comments. I agree that having a spare wire in a cable doesn't mean you have to use it if it is not necessary to comply with code. I was considering using the armor and the wire EGC in the cable, connected in parallel, if you will, to double the total size of the EGC, so as to comply with 250-122(F) when paralleling two MC cables. "don_resqcapt19" makes an interesting point. If the aluminum armor is listed as an acceptable EGC, it could be treated as a conduit, which isn't required to be a particular size, when paralleling runs. Therefore, by this logic, the size of the wire EGC in an MC cable is irrelevant when using MC cable in parallel runs. I can't see this as a good installation even if it may be legal. Anyone have any thoughts on this?

 

[don_resqcapt19]

Thank you all for your comments. I agree that having a spare wire in a cable doesn't mean you have to use it if it is not necessary to comply with code. I was considering using the armor and the wire EGC in the cable, connected in parallel, if you will, to double the total size of the EGC, so as to comply with 250-122(F) when paralleling two MC cables. "don_resqcapt19" makes an interesting point. If the aluminum armor is listed as an acceptable EGC, it could be treated as a conduit, which isn't required to be a particular size, when paralleling runs. Therefore, by this logic, the size of the wire EGC in an MC cable is irrelevant when using MC cable in parallel runs. I can't see this as a good installation even if it may be legal. Anyone have any thoughts on this?

If you use the internal EGC it must comply with 250.122(F). The equipment grounding conductor in a standard cable will not be in compliance.
There is no provision that would let you parallel the EGC and the cable jacket to comply with 250.122(F).

 

[GoldDigger]

If you use the internal EGC it must comply with 250.122(F). The equipment grounding conductor in a standard cable will not be in compliance.
There is no provision that would let you parallel the EGC and the cable jacket to comply with 250.122(F).

But do you concur that if you use only the cable jacket EGC it is presumed to be adequate?
Or would the presumption fail when it is part of a parallel conductor set?

 

[don_resqcapt19]

But do you concur that if you use only the cable jacket EGC it is presumed to be adequate?
Or would the presumption fail when it is part of a parallel conductor set?

The code does not say you have to do anything special to any EGC, other than an EGC of the wire type, for parallel installations.
If the use of the cable jacket or a metallic raceway, as the EGC for a parallel circuit, is an issue, then the 250.122(F) should be changed to require an EGC of the wire type for paralleled installations.