EGC Size for Parallel Feeder

[Trey4U]

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?

 

[LarryFine]

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?

 

[Trey4U]

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?

 

[Dennis Alwon]

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.

 

[petersonra]

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)

 

[texie]

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.

 

[Trey4U]

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?

 

[texie]

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.

 

[Trey4U]

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.

Thanks, that's what I missed and needed.

 

[Trey4U]

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.