lauraj
Senior Member
- Location
- Portland, Oregon
This is a theoretical question and I can't find any reference in the NEC for this.
112.5KVA, 480-208/120V xfmr feeding a panel with a 300A main breaker with 350kcmil conductors. System bonding jumper is located in the transformer.
If a grounded conductor is pulled, what is the smallest size it could be?
I say we must use T250.102(C)(1) and it would be a #2 CU, because if we had a line to neutral fault at the panel, it would need to be big enough to carry that fault current. But I sure can't find anything that tells me I need to use that table. 250.30(A)(2) which give minimum neutral conductor requirements for SDSs only applies if the system bonding jumper is not located at the transformer.
112.5KVA, 480-208/120V xfmr feeding a panel with a 300A main breaker with 350kcmil conductors. System bonding jumper is located in the transformer.
If a grounded conductor is pulled, what is the smallest size it could be?
I say we must use T250.102(C)(1) and it would be a #2 CU, because if we had a line to neutral fault at the panel, it would need to be big enough to carry that fault current. But I sure can't find anything that tells me I need to use that table. 250.30(A)(2) which give minimum neutral conductor requirements for SDSs only applies if the system bonding jumper is not located at the transformer.
