Old 12-10-11, 09:28 PM
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I was reading the code and I don't under stand what derating is and how it applies.

Why is it allowable to derate neutral, relative to the line wires?
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Old 12-11-11, 06:07 AM
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Derating is a compensation for the inability to radiate heat because the cables or wires are close together or are in a high heat area. The ampacity is reduced.

The neutral is sometimes allowed to be smaller than the ungrounded conductors due to not all circuits need a neutral.
Old 12-12-11, 08:28 PM
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Typically, you only have to be concerned with derating if you're running more than 9 current carrying (hot & neutral) wires in one channel (usually conduit). When you pull NM-B through studs/joists, you want to limit it to no more than 3 (or 4) cables through a single hole across a few studs or joists.

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