NEC 1999, APPENDIX D, Example D1(b)

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I am reading NEC 1999, to take test, and in Appendix D, example D1(b) confuses me. Why the book is using 10 A for neutral of dishwasher and AC ( both 120V), and why using 3,2,2 for 25% of largest motor? Is dishwasher the largest motor? Is waste disposer the largest motor?

charlie b

Staff member
Seattle, WA
Electrical Engineer
Re: NEC 1999, APPENDIX D, Example D1(b)

They treated the two machines (room A/C unit and dishwasher) as though the two constituted a single motor. But they used 10 amps for the neutral by mistake. Their note says to use the larger of the two, so they should have used 12 instead of 10. That error was corrected in the 2002 code.

Since the two machines are being treated as a single motor, and since it is larger than the 230V A/C unit and larger than the disposer, you take 25% of the current from each leg. 25% of 12 is 2, and 25% of 10 is 2.5. I think they should have rounded the 2.5 up to 3, but they rounded it down to 2. In the 2002 code book, the same example shows the three currents as 12, 12, 10, and the 25% factor as 3, 3, 2.

[ March 03, 2003, 12:00 PM: Message edited by: charlie b ]
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