Nec

[Khalid Ahmed]

Question: If you have a 3KVA single phase transformer with 480V primary protected with a fused disconnect and 120V secondary feeding a 120V fractional hp sump pump does the secondary of the transformer require a overcurrent protection ,the pump is less then 10 feet from the transformer?
Please refer to code section.

 

[david luchini]

If the primary fuses where 10A or smaller, then the transformer wouldn't require secondary protection per 450.3(B).

Assuming the 10A fuse on the primary, the secondary conductors would need to have an ampacity of at least 40A, in order to be protected by the primary OCPD, per 240.21(C)(1).

However, I'm not sure that the motor would be properly protected by the primary OCPD. Maybe someone else could shed some light on that.