Overcurrent device sizing Why doesn't the Code permit using the next highest size overcurrent device where the ampacity of the conductor does not match a standard overcurrent device, if the next higher standard rating exceeds 800 amperes (A)? Overcurrent devices below 800A are available in ratings increments that don't exceed roughly 18 percent and are gen erally much less than that. Overcurrent devices rated 800A and above are generally increased in size by a much greater degree to a point where allowing the next higher size is not practical. For instance, the next higher size over 700A is 800A, an increase of 100A. However, the next higher size over 800A is l,000A, an increase of 200A, and the increments become progressively greater. Check out NEC 240.6.
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