Transformer Room 450.21(B)

[Junior_EE]

We want to install a 225kVA dry type transformer in a mechanical room. According to NEC 450.21(B), code says the transformer needs to be in a transformer room with a 1hr rating.

My question is what is your interpretation of a transformer room? I interpret this to mean a dedicated electrical closet or room with a 1hr rating, with only electrical equipment inside of it. Some colleagues feel that the transformer can sit in a mechanical room if the mechanical room has a 1hr rating. There does not appear to be a definition of a transformer room in the NEC.

 

[augie47]

Check the 450.21 Exceptions. I would not be surprised to see your transformer met one of the exceptions.

 

[Junior_EE]

Check the 450.21 Exceptions. I would not be surprised to see your transformer met one of the exceptions.

I've looked into that but do not know how difficult it is to find a plain NEMA 1 transformer with Class 155 insulation.

Let's assume we can't find a transformer with Class 155 insulation. Can this transformer sit within the mechanical room?

 

[petersonra]

I've looked into that but do not know how difficult it is to find a plain NEMA 1 transformer with Class 155 insulation.

Let's assume we can't find a transformer with Class 155 insulation. Can this transformer sit within the mechanical room?

I think the standard acme distribution transformers are class 220 insulation.

Look at exceptions 1 and 2. Neither requires a transformer room at all.

 

[jim dungar]

I've looked into that but do not know how difficult it is to find a plain NEMA 1 transformer with Class 155 insulation.

I think it is harder to find one that isn't.