3 phase loads and reduced neutrals

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Apothe

Engineer
Joined
Oct 11, 2016
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New York City, NY
Let's say I have a 120/208V 3Ø 4W 100A panelboard serving an area.

On this panel I put a 40A 208V 3Ø motor and the rest of the loads on this panel are 120V single breakers, lets say they're non linear so there is current in the neutral.

Per NEC I have to bring 3#3 AWG wires to this panel, but can I technically use a 60A neutral now?

My reasoning for this is that 40A is gonna be dissipated into the motor and doesn't have a return wire to the neutral bar, while all the other loads on the panel have return wires.

May sound stupid but what is your guys take on this?

 
I think, but could be wrong, that you size the neutral for the expected unbalanced/harmonic current in the Neutral.

 
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