I have a 75kva 3 phase 480v to 208/120v transformer. Secondary full load amps is 208amps. Can the secondary be landed to a 225amp MB panelboard even if it can never reach that ampacity? I read over 240.21C and the secondary conductors have to be the ampacity of the rating of the equipment. I can't find anything that says this isn't legal.
Transformer secondary OCP
- Thread starter stephena
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electrofelon
Senior Member
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- Cherry Valley NY, Seattle, WA
Sure no problem, as long as your conductors are sized for an ampacity of at least 225. Assuming the MB is protecting the transformer secondary, you would need to check that value too, but in your case per 450.3 (B) the worse case would be 125% transformer current so you are well within that.
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