Transformer secondary MOCP

[sevlander]

What is the maximun overcurrent protection allowed an the secondary of a 45KVA 480-120/208V 3PH transformer? I believe it is 125A , but a plan we are bidding is calling to replace the existing 100A 120/208 panel with a 150A MCB panel using the existing transformer. The transformer secondary amps are listed as 125, how can this be allowed at 150A? Is the MOCP 125% of the 125A nameplate? I was always taught that this nameplate amperage is already at max and the 125% cannot be used. Please advise where it is shown in NEC if I am wrong. Thanks

 

[ron]

Take a look at 450.3(B)

 

[jim dungar]

There is no restriction on the size of a protective device on the secondary of a transformer, when the primary side device is limited to 125% maximum.

If you desire to increase the primary protective, then and only then is a secondary device required and it is limited to 125%.

Of course, these rules do not address the protection of the secondary conductors, for that you need to look at 240.21(C).