Sizing Neutral

[augie47]

When I wore a younger mans clothes and did this every day this question was child's play but old brains don't work as well as younger ones
400 amp 240/120 single phase service commercial building.
No load calculations have been made.
Service conductors will be parallel in one conduit.
220.61 allows the neutral to be sized at 200 amps + 70% of 200 amps or 340 amps,
Neutral is not considered to be current carrying (unbalanced load) so no fill adjustment required for neutral.
Question:
Since the neutral does not terminate on a device using 90deg conductors can the neutral be reduced to 3/0AL (175 X 2) or is it required to comply with the 75deg rating ?

 

[infinity]

This section confuses me, why can't 220.61(A) apply? If that because there is not a load calculation?

220.61(A) Basic Calculation.
The feeder or service neutral load shall be the maximum unbalance of the load determined by this article. The maximum unbalanced load shall be the maximum net calculated load between the neutral conductor and any one ungrounded conductor.

 

[wwhitney]

I raised this question on 90C terminations for the grounded conductor back in 2022:

90C ampacity usable for grounded conductor?

Say you have a feeder between panelboards. Typically at least one end of the ungrounded conductors will landed on a breaker which has max 75C rated terminations. But the grounded conductor may run from one neutral bar to another. Are those neutral bar terminations possibly rated 90C? If so...

forums.mikeholt.com

There was no definitive response, but responses overall leaned towards only 75C rating.

Cheers, Wayne

 

[suemarkp]

Any 2 pole loads you can subtract off? Kind of hard to know how much to take off with no calc to see if some demand factor is applied to any 240V loads, but I would think you have some to work with.

 

[augie47]

So with no load calculations my 400 amp service would require parallel 300 kcmil AL (as I can't assume a load less than 400 amps ) with parallel 250 AL neutral