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NEC 240.21 says all ungrounded circuit conductors require overcurrent protection, with a list of exceptions:

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One of those exceptions is 240.21(C):

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240.4(B) says that if you're under 800 amps, you can up-size your breaker to the next available size. But what I don't understand is the text of 240.21(C). It says the conductors connected to the secondary don't have to have protection, and also that the up-sizing of the (non-existent) protection isn't allowed. Why would you say "You're not allowed to up-size the breaker" right after saying "You're not required to have a breaker at all?" I must be misunderstanding something.

Stephen Collings
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  • Is there meant to be an extract of 240.4(B)? – Andy aka Oct 28 '21 at 07:24
  • No, I left it out because the text didn't seem particularly relevant. – Stephen Collings Oct 28 '21 at 13:00
  • I have seen comments saying that NEC stands for "not exactly clear." I agree that it can sometimes be pretty difficult to interpret. I would recommend looking at everything in the code that is related to the question. Sometimes it helps to carefully consider the complete context. Also consider forums like https://forums.mikeholt.com/forums/nec/ . Note that such forums only welcome questions from "people in the field." The NEC handbook might help. The IEEE 3000 Standards Collection™ is a series of recommended practices that might help. –  Oct 28 '21 at 13:56

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