NM-B cable temp / amp ratings

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Trowbridge - Martin

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Dear Forum, United Copper Industries quotes this: Type NM-B (Nonmetallic-sheathed Cable) may be used for both exposed and concealed work in normally dry locations at temperatures not to exceed 90?C (with ampacity limited to that for 60?C conductors) as specified in the National Electrical Code.
For years an a/c unit in an attic with a 10k heater and 60 amp brkr has used #6 nm-b cable up to 65 amps (90c). At 60c we will have to use #4 nm-b now ?
Thank you
 
In my experience it depends somewhat on your air handler. I see some with 10kw heat and a MCA of 55 or less and some with a MCA greater than 55.
#6 NM Cable is limited to a 60? ampacity of 55 amps (as is SE in the '08 Code).
Any MCA greater than 55 would require a larger cable.
 
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