MCB for Distribution Panels fed from Aux Transformer

[kvramesh]

We got an mining facility at 4500m altitude asl. We got some panels 380V/219V, 50Hz fed from a 380V-380/219V, 75kVA, 3.1% aux transformer. The only protective device for the xfmr and panel is incoming breaker of xfmr which is 175amps fed from our MCC.

The distance from incoming breaker to xfmr is about 40ft while the panel and xfmr are next to each other. I referred to NEC 450 and 240.21 for xfmr protection and cable protection...I'm lil bit confused with various options on xfmr primary and secondary protection.

Could anyone assist me if I need to put a main CB in the panel or my incoming breaker should do? It's not about $, but looking at code requirement.


Thanks in advance

 

[raider1]

The overcurrent protection for the panel must be located on the secondary side of the transformer (See 408.36(B))

Also the secondary conductors from the transformer to the panelboard must be protected by one of the methods specified in 240.21(C)(1) through (6).

Chris

 

[chris kennedy]

Chris, although highly unlikely, you didn't ask if the install was underground.

 

[raider1]

Chris, although highly unlikely, you didn't ask if the install was underground.

You are correct, but the requirements for transformer secondary conductors run outside is located in 240.21(C)(4).

Chris

 

[kvramesh]

Nothing is underground. The transformer and panel will be sitting in an electrical room

 

[kvramesh]

We found out that inserting main breakers is not possible but we will have to buy new panels. So, I am considering if it is acceptable according to NEC or engineering practise without main breaker inside the panel but use the main breakers on the transformer...please advise

 

[raider1]

We found out that inserting main breakers is not possible but we will have to buy new panels. So, I am considering if it is acceptable according to NEC or engineering practise without main breaker inside the panel but use the main breakers on the transformer...please advise

The OCPD for the panelboard must be located on the secondary side of the tranformer. You can install a disconnecting means ahead of the panelboard that would contain the OCPD for the panelboard and also meet the requirements for the transformer secondary conductor requirements from 240.21(C).

Chris