transformer secondary protection

[Jeff Degitz]

When feeding a transformer from a 480/277v service {MDP} and tapping the transformer to provide 208/120v power to a panelboard, is a main breaker required in the panelboard? Overcurrent protection is provided on the primary side of transformer from MDP. Is secondary overcurrent protection required if all these components are grouped together?

 

[fc]

Re: transformer secondary protection

Yes you would need Overcurrent protection on your secondary.
Look at NEC 250.21 (C)

 

[volt101]

Re: transformer secondary protection

Overcurrent is provided at the feeder to the transformer, what is the rating?
Take a look at 450.3(B)

Jim

 

[fc]

Re: transformer secondary protection

sorry I ment to say 240.21 (c)(1)Protection by Primary Overcurrent Device. Conductors supplied by the secondary side of a single phase transformer having a 2-wire (single voltage) secondary, or a three phase delta-delta connected transformer having a 3-wire (single voltage) secondary, shall be permitted to be protected by overcurrent protection provided on the primary (supply) side of the transformer, provided this protection is in accordance with 450.3 and does not exceed the value determined by multiplying the secondary conductor ampacity by the secondary to primary transformer voltage ratio.
Single phase ( other than 2-wire) and multiphase (other than delta-delta 3 wire) transformer secondary conductors are not considered to be protected by the primary overcurrent protective device.
I think you have 480 primary 120/208 secondary 3 phase system sp you would need secondary protection.