Sizing neutrals

[sig2008]

A building is supplied with a 400 amp 3 phase 208Y/120V 4 wire service with the ungrounded conductors size 500 kcmil copper. The maximum calculated unbalanced load for the building is 20 amp. Determine the minimum size copper neutral conductor for the service.

 

[roger]

Show us how you would go about getting the answer and we will tell you if your right or we will help you find the answer.

Roger

 

[Smart $]

...The maximum calculated unbalanced load for the building is 20 amp...

The quoted sentence of your post suggests you have no more than three 20 amp single phase loads (where each is supplied by a different phase). That's not much for a 400 amp service!

There also seems to be a question you didn't ask?

Additionally, we can't determine the maximum unbalanced load with the little information you provided.

For reference on sizing the grounded service conductor, 250.24(C)(1) requires size not be smaller than required GEC size specified in T250.66.