Transformer sizing & continuous loads

[cppoly]

If you have a 30 kVA continuous load (lighting), you can use a 30 kVA transformer right?

But the secondary conductors and OCPD need to be sized at 125%.

OCPD = 83A x 1.25 = 104A = next size up 110A. So let's say you give 42-pole 225A panelboard with 110A main breaker.

1) Is this OK have 110A OCPD but the transformer secondary can't exceed 83A?

2) Doesn't this give the illusion (at least to someone else) that the FULL 110A can be utilized if they see a 42-pole panelboard with 110A main breaker? Can't the panel be loaded up to 110A amps, then you get 39.6 kVA calculated load which would exceed the 30 kVA transformer rating.

 

[EC Dan]

Sure but that's a design issue not a safety issue which is what the NEC is concerned with. Drawing more than a transformer can supply will cause voltage sags, but as long as the conductors are sized appropriately it's not a safety concern.

 

[David Castor]

The continuous rating of a 110 A breaker in a panel is 88 amps (80%).