EGC Size for Parallel Feeder

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Trey4U

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Alabama
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Retired Electrical Contractor
I have a 500 MCM parallel feeder cable type TC-ER. The EGC in each cable is a #2. The 800 amp breaker requires a 1/0 EGC based on Table 250.122. When I double the circular mil area of the #2's I'm just shy of the circular mil area of 1/0. I'm sure I need to run another EGC external to the two feeder cables but am unsure what size. The area of two #2's is 132738. The 1/0 is 133072, for a difference of 334 circular mils. What size additional EGC do I need?
 
The general rule for parallel conductor installations is that each EGC must be sized as if it was the only one, which is a common problem when paralleling cable assemblies.

Is there an alternate EGC available, like a cable tray or metallic conduits?
 
The general rule for parallel conductor installations is that each EGC must be sized as if it was the only one, which is a common problem when paralleling cable assemblies.

Is there an alternate EGC available, like a cable tray or metallic conduits?
No, this is direct buried and we found the issue on an inspection.

I was under the impression that one external EGC could be used and it has to be sized per Table 250.122 which in my case would be one 1/0. but since I have two #2's I'm not sure what I need.

Anyone have a Code reference?
 
Your equipment grounding conductor must be large enough to trip the 800 amp breaker so each cable must have the full size equipment grounding conductor.
 
No, this is direct buried and we found the issue on an inspection.

I was under the impression that one external EGC could be used and it has to be sized per Table 250.122 which in my case would be one 1/0. but since I have two #2's I'm not sure what I need.

Anyone have a Code reference?
250.122(F)
 
Yes, 250122(F)(2) would a allow this if you are using NEC 2017 as this allowance was added then. We had the question arise if was this allowed in a trench as trench is not specifically mentioned. Our AHJ thought a trench was similar to the requirement and allowed it.
 
I still don't know what size additional EGC is required. If I have in place the two #2's in the cables do I still need two 1/0 EGC's? The #2's don't matter?
 
I still don't know what size additional EGC is required. If I have in place the two #2's in the cables do I still need two 1/0 EGC's? The #2's don't matter?
You just do what it says in 250.122(F)(2)(a) and (b). You use a single 1/0 in addition to the EGCs in the cables all connected at each end.
 
Yes, 250122(F)(2) would a allow this if you are using NEC 2017 as this allowance was added then. We had the question arise if was this allowed in a trench as trench is not specifically mentioned. Our AHJ thought a trench was similar to the requirement and allowed it.
I missed that you posted the Code reference I needed, thanks.
 
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