225kva xfmr installation

[jibron]

I’m using a 225kva to step up 208 to 480/277 wye.
450.21 (B) is telling me I need to construct a transformer room unless I qualify for the exception calling for “Class 155 or higher insulation systems “ on my transformer. Can someone tell me what exactly that is? Here is my tag.

 

[d0nut]

You have 220 degC insulation with your transformer.

 

[winnie]

Something that the requirements don't make explicitly clear. You have a 'NEMA insulation class'. It just happens that the insulation class number is the same as the max temperature allowed in degrees C.

NEMA Insulation Classes for Transformers

Transformer Insulation class, NEMA Insulation class

www.electricalengineeringtoolbox.com

So when the dataplate says 'Temp Class 220°C' that implies a NEMA insulation class 220, which exceeds NEMA insulation class 155

-Jon

 

[petersonra]

I don't think the manufacturers even make a dry type power transformer at less than class H insulation.