Sizing the grounding and grounded conductors for a 480V 3W from Y transformer

[lakee911]

Utility is supplying a Wye-Wye transformer. I originally specified the following from the transformer secondary to the main disconnect: 3-(350MCM/phase,#1/0G,3?C). That's three sets of 350MCM per phase and 1/0 ground in a 3" conduit.

Contractor thinks a nuetral (grounded) conductor is required. Yes, it is required. My mistake.

I check my work .... I do not have any 277V loads and I'm only taking three wires from the switchgear so my unbalanced nuetral load is 0A.

So, I size the neutral (grounding conductor) per Table 250.66: 350 kcmil copper shows 1/0 copper ground. Ok.

I size the neutral (grounded conductor) per 220.61(A): the unbalanced load = 0A. For that, 250.24(C)(2) allows me to use a minimum size of 1/0 copper.

Am I correct?

3-(350MCM/phase,1/0,1/0G,3?C) or three sets of 350MCM per phase, plus 1/0 grounded conductor and 1/0G grounding conector. (I know it might be tough to pull, but it's a short distance).

Thanks!

 

[chris kennedy]

3-(350MCM/phase,1/0,1/0G,3?C) or three sets of 350MCM per phase, plus 1/0 grounded conductor and 1/0G grounding conector.

From utility secondary to gear you only need one 1/0. Could be reading this wrong, but there is no EGC between POCO secondary and the main disco.

 

[Smart $]

Deleted...

 

[bob]

Utility is supplying a Wye-Wye transformer. I originally specified the following from the transformer secondary to the main disconnect: 3-(350MCM/phase,#1/0G,3?C). That's three sets of 350MCM per phase and 1/0 ground in a 3" conduit.

Contractor thinks a nuetral (grounded) conductor is required. Yes, it is required. My mistake.

I check my work .... I do not have any 277V loads and I'm only taking three wires from the switchgear so my unbalanced nuetral load is 0A.

So, I size the neutral (grounding conductor) per Table 250.66: 350 kcmil copper shows 1/0 copper ground. Ok.

I size the neutral (grounded conductor) per 220.61(A): the unbalanced load = 0A. For that, 250.24(C)(2) allows me to use a minimum size of 1/0 copper.

Am I correct?

3-(350MCM/phase,1/0,1/0G,3?C) or three sets of 350MCM per phase, plus 1/0 grounded conductor and 1/0G grounding conector. (I know it might be tough to pull, but it's a short distance).

Thanks!

You only need a neutral from the transformer to the main switch. Just convert the 1/0 to a neutral(grounded conductor).

 

[lakee911]

Thanks.