In the 2002 code 450.21(B) a room must be fire rated (1 hour) if a dry type transformer larger than 112.5 KVA is installed in it. Exception No. 2 allows transformers larger than 112.5 KVA installed in an un-rated room if the transformer has a class 155 insulation system and enclosed except for ventilation openings. The transformer manufacturer I am looking at does not have a class 155 rating, however it does have a class R rating which has a 220 deg C insulation system with 150 deg C temp rise. Does the class R rating of the manufacturer (Cutler Hammer) meet the Class 155 rating refered to in the code? Is there a cross reference between these class type insulation systems somewhere? I do not have access to the ANSI/ASTM-1995 or NFPA 251-1999 refered to in the FPN in this section.
transformer rating
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kingpb
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My suggestion would be to contact the CH rep and ask him to find out. They have technical guys in their organization, and should be able to gte an answer to this for you very quickly. Especially if he knows it it means you can't buy his equipment otherwise.
Section 450.21(B) Exception No. 2 applies to transformers with a Class of insulation that is equal to, or exceeds Class B insulation, Class R exceeds Class B. To determine the insulation Classification add the temperature rise above a 40 degree ambient and then add a 35 degree hot spot, i. e., Class B = 80 + 40 + 35 = 155. I have not seen a modern transformer that does not meet Exception No. 2.
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