Neutral sizing in 3P/4W System

[seamus000]

Have reviewed previous postings, but...

120/240 3p/4w system feeding 120/240 distribution panel (all 1p loads, not particularly balanced, and a pump control panel (2 motors powered from 3 phases with no neutral connection, 120v 1p control equipment powered from A-leg to neutral from power company transformer.)

1)What are the rules (NEC) for sizing the neutral conductor? particularly from the power company transformer through to the dist panel and to the PCP?

2) is this concidered to be a current-carrying conductor? does it need to be considered in sizing all four conductors back to transformer (in conduit)? i.e. do i need to derate ampacities by 80%?

Thank you in advance.

 

[RajT]

In your case the simple answer is to size the N conductor the same as the phase conductor.

 

[resqcapt19]

If this sytem in 120/240 with a wild leg, the grounded conductor is not a current carrying conductor. If this is a 3 phase wye system feeding a single phase panel the grounded conductor is a current carrying conductor. The code in 220.22 says you size the grounded conductor based on the maximum net computed load between the neutral and the ungrounded conductor with the largest load.
Don