Transformer Secondary Protection

[trallio]

Is secondary overcurrent protection required for either of the two following conditions?

1. 480V single phase primary protected at 125%FLA with a 240/120V Secondary.


2. 480V 3phase primary protected at 125%FLA with a 120-208V secondary.

 

[fc]

Re: Transformer Secondary Protection

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

 

[don_resqcapt19]

Re: Transformer Secondary Protection

Transformer secondary protection is not required in either case, however, as pointed out by FC, the secondary conductors require protection. This is an area where many code users just look to Article 450, when they need to be looking at both 450 and 240.
Don