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Old 05-07-2008, 02:29 PM   #1
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Diameter hole for 4 * 12/2 MC


Is there somewhere I can find out the proper hole diameter through a joist, and/or max # of wires per hole without derating?

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Old 05-07-2008, 03:19 PM   #2
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Diameter hole for 4 * 12/2 MC


In the I-codes, holes can be drilled through joists. The holes must not exceed one third of the joist's depth, and must not be any closer than 2" to the top or bottom chord.

As far as wiring goes, you need to avoid bundling. I'd have to dig for code language to substantiate this, but I'd limit it to 2 or 3 wires per 1" hole. The less, the better. Drilling a few smaller holes a few inches apart will always be the best way to go, as opposed to pulling several wires through the same hole.

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Old 05-07-2008, 03:38 PM   #3
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Diameter hole for 4 * 12/2 MC


Up to four cables before you need to be concerned about derating.
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Answers based on the 2008 & 2011 NEC.
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