Control Transformer

[infinity]

I have a 480/120 volt, 1kva transformer to provide power for a motor operated circuit breaker. The control transformer is fed from a 480 volt, 1600 amp switchboard. There will be primary and secondary protection, do any tap rules apply?

 

[tom baker]

I will typically see this type application in an MCC, power to the transformer is tapped off the secondary side of the MCC disconnect, then with primary fusing, but the fuses are current limiting, and this is a UL 508 application. Your question, I am not sure about.

 

[tkb]

I have a 480/120 volt, 1kva transformer to provide power for a motor operated circuit breaker. The control transformer is fed from a 480 volt, 1600 amp switchboard. There will be primary and secondary protection, do any tap rules apply?

Yes, 240.21(B)(1)
If the tap doesn't leave the enclosure the size of the conductors can be sized to your transformer's primary protection.

 

[infinity]

Yes, 240.21(B)(1)
If the tap doesn't leave the enclosure the size of the conductors can be sized to your transformer's primary protection.

Ahh yes I forget about the conductors not leaving the enclosure which these do not therefore the 10% conductor rule does not apply. Thank you.