XMFR Sizing

[jim dungar]

OK, if that's the scenario you've been discussing.

I have just been following the OP. I was not trying to go into the weeds, unless the OP was willing to go along.

Who said the NEC calculated load was 38,400VA?
There are no facts in evidence as to where this number came from.

 

[wwhitney]

Who said the NEC calculated load was 38,400VA?
There are no facts in evidence as to where this number came from.

True. I was asserting it as a hypothetical for my example, and am apparently happy to go into the weeds : - )

Anyway, my point is that the NEC does impose a lower bound on transformer rating based on the NEC calculated load, so transformer size is not purely a design choice. The NEC lower bound is not more than 80% of the calculated load, so in practice it's likely not to be a controlling constraint.

Cheers, Wayne

 

[electrofelon]

What NEC section says that the transformer rating must be at least the calculated load on the transformer?

There is more general wording in 110.3(A) that requires equipment be examined for suitability , including it's current capacity. It doesn't specifically say how the applied current level is determined. Perhaps some AHJ's would assume the load calc would be used. There are actually only a few things in the code that are required to be protected at their rating by an OCPD, for most other things this section is what would apply.