220.61 clarification

[pgordon]

I have been asked to replace a 400a 480/277v ATS with (3) 500 MCM (1)3/0 CU conductors.
This neutral is rated at %50 , I am use to seeing %70 long ago and hardly ever see it these days.
This feeder supplies a HVAC / Light panel with only 3 or 4 277v lighting circuits .
220.61 talks about sizing the neutral for the unbalance, is this why it is reduced so much ?
220.61b talk about %70 reduction in excess of 200a .
I find this confusing , Please explain , Thx Paul

 

[Dennis Alwon]

The 70% refers to the portion of the unbalanced load in excess of 200 amps. I don't see how the neutral load will be in excess of 200 amps.

The neutral can be sized as small as the grounding electrode conductor for a service and as small as the equipment grounding conductor for a feeder provided the loads are not higher than the ampacity of those conductors