Neutral Load VA divided by Phase to Phase voltage

[xformer]

What is the justification for deriving the neutral load amps by dividing the phase to phase voltage on a single phase system?

 

[wwhitney]

What is the justification for deriving the neutral load amps by dividing the phase to phase voltage on a single phase system?

Let's assume 120V/240V. If you had all 120V loads and a total load of say 12000 VA, that would be 100A @ 120V. You're supposed to balance the load equally across both ungrounded legs, so that would be 50A supplied L1 - N and 50A supplied L2 - N. That makes the maximum neutral load the same as the maximum load on each ungrounded leg--they are all 12000 VA / 240V = 50A.

When you have 240V 2-wire loads, you can leave them out of the above as far as determining the neutral load. And for 120V/240V 3-wire loads, Article 220 has some guidance on what fraction of the total load you need to consider for determining the neutral load--the balance is assumed to be supplied with 240V 2-wire internally.

Cheers, Wayne

 

[xformer]

Thanks Wayne