NEC 450.21B

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electrical irishman

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In this code it state "Individual dry type transformers of more than 112 1/2 kVA rating shall be installed in a transformer room of fire-resistant construction. Unless specified otherwise in this article, the term fire resistant means a construction having a minimum fire rating of 1 hour. Exception No.1: transformers with Class 155 or higher insulation systems and separated from combustible material by a fire-resistant, heat-insulating....."

Okay my question is; is the code talking about the temperature rise or the system temperature that the transformer says it is rated for?
 
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electrical irishman

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Re: NEC 450.21B

Sorry I spoke too soon. The transformer I am talking about is a 300kVA dry type transformer. It is rated on the label for 150 deg.C. temperature rise and a 220 deg.C. system. So this transformer is a Class 220 right?
 
charlie b

charlie b

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Re: NEC 450.21B

I don?t have a copy of UL 1561 handy (?Dry-Type General Purpose and Power Transformers?). That might be the best written source of information to resolve the question of whether your transformer meets the NEC statements regarding ?Class 155 or higher.? You could also ask your transformer?s vendor or manufacturer to clarify its rating.

But looking at the link provided by Russ, it appears that a transformer rated for 150 C temperature rise should be at least a ?Class 180.? From this, I infer that the Exceptions to NEC 450.21 should apply. The bottom line is that if the transformer itself can handle the heat, and if there is nothing combustible nearby (i.e., something that might not be able to handle the heat), then you don?t need a 1-hour fire-rated room.
 
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