Transformer Derating & Secondary Protection

[SG-1]

If you have a transformer in a high ambient temperature such that it must be derated to 80% of its kva rating, should you use the derated value of the output current to size the secondary breaker?

Or, would you use the 100% value before derating ?

Example:
15kva transformer with a 240/120 secondary.
Should the secondary breaker size be based on 62.5Amps or 50Amps ?

 

[bob]

I would think that you would use a breaker, primary/secondary, that would limit the amperage to the 80% value.
The FLA would not be available. Therefore the conductors would be based on the 80%. I did not see a specific NEC
article that covered this situation.

 

[SG-1]

Thank you, Bob. Appreciate the responce.