450.21 (B) EXCEPTION 1&2

[daveatuconn]

Is the class 155 or higher insulation rating in exception 1&2 of article 450.21 (B) a temperature rating, or is it referring to a different classification?

 

[jim dungar]

Re: 450.21 (B) EXCEPTION 1&2

I believe it is refering to the insulation class of the transformer windings, not the temperature rise of the transformer.

Standard transformer insulation:
Class A = 105C max permissable temp/55C rise
Class B = 150C max permissable temp/80C rise
Class F = 185C max permissable temp/115C rise
Class H = 220C max permissable temp/150C rise