3 PHASE DISTRIBUTION FEED WITH A REDUCED NEUTRAL

[ED-GEE]

Can anyone clarify and show example of a 3 phase 400A feeder with a reduced size neutral? is that even allowed by NEC?

 

[Engineer1916]

ED-GEE,
You need to find the unbalanced current first. But lets assume that you can connect a 400A single phase load on 3 phase 4 wire system, then your unbalanced load is 400A. NEC 220.61(B)(2) allows 70% on neutral current in excess of 200A. So your neutral current in this case will be 340A.

 

[waross]

The transformer jumpers from the transformer terminals to the wye point connection carry the same current as the phases and should not be reduced in size.

Bill
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