Sizing grounded conductor

[ShockMonkey]

I don't know if I'm overthinking this, but I'm a little befuddled.

Say I wanted to size the grounded conductor for a 480-volt, 600-amp service with two parallel runs of 350 kcmil. Would it be as simple as going to Table 250.102(C)(1) and selecting #2 wire as the grounded conductor (one for each run), or do I have to mess with 220.61 and the maximum unbalanced load? What if I don't what the loads will be?

 

[don_resqcapt19]

You have to do both methods and select the larger of the two. You will have to have some idea of what the line to neutral loads will be.
What type of facility? At that voltage the only common line to neutral load would be lighting.

 

[augie47]

+ if you are paralleling the grounded conductors, 1/0 is the smallest allowed.

 

[ShockMonkey]

You have to do both methods and select the larger of the two. You will have to have some idea of what the line to neutral loads will be.
What type of facility? At that voltage the only common line to neutral load would be lighting.

It's more of a hypothetical situation. I'm just trying to wrap my head around it.

 

[augie47]

Keep in mind the conductor has to be large enough to carry the load and that can only be assured by calculation the load.
You might 220.61 has some provisions for reducing the wire size.
In addition the service neutral is serving as your ground fault return path so it must be sized accordingly as you noted 250.102.

 

[ShockMonkey]

+ if you are paralleling the grounded conductors, 1/0 is the smallest allowed.

Doh! I forgot about that. Thanks!

I think I have a better grasp now. I was confused by the two requirements and didn't see that both needed to be followed.