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Electrical Code - USA Commercial or Residential 1999 / 2002 / 2005 versions - for UNITED STATES

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  #1   IP: 68.37.48.49
Old April 17th, 2008, 05:10 PM
Logcabin1 Logcabin1 is offline
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Red face How many wires can I string through a single hole in a joist/stud?

Sounds like the lead into a Polish joke....

I'm pulling wire to juice my addition and have a couple questions on standard practices.

I understand most of the basic rules -- not drilling holes closer than 1 1/4" from edge of studs and bottom and top plates (without metal stopper), I think that I'm supposed to limit the size of hole to 1/3 of width. With 2" x 4" studs I'm generally using 1" hole to stay 1 1/4" from either side.

If running through 2" x 10" joists I'm placing the hole in the middle third depth and staying at least 2" from the ends. Do I also need to stay on the outside third of the span? In other words, if I have a 12 foot span, do I need to drill holes between 0-4 ft or 8-12 ft? Are there other rules I need to abide?

How many wires can I string through a single hole. Is there a limit or can I string through as many as fit? Am I better off drilling multiple holes next to each other or squeezing them in? My current plan has me using a couple bays to run many wires up the vertical using plastic stackers. Should I squeeze the wires through one or two holes or should I go the swiss cheese approach on bottom and top plates of a non-load bearing wall?

The circuit wire is 12/2wG and 14/2wG.

Your thought would be greatly appreciated!

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  #2   IP: 76.104.172.149
Old April 17th, 2008, 09:33 PM
suemarkp suemarkp is offline
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In insulated cavities, the cables will be considered bundled. This limits you to 4 cables per hole before you have to derate and use a smaller breaker than normal.

In an open floor, you could probably do more, but "bundled" isn't well defined in the code. To be safe, limit yourself to 4 cables in all holes, or call the inspector first asking if what you're doing is "bundled". My joists are 12" on center, so the wires look bundled to me. A 24" spacing would be harder to judge.

Generally, a 2" hole in a 2x10 and be anywhere along its span (just keep it in the center of the 9" depth). Usually, they don't like holes in line with the bearing surface (so stay a bit away from the end of the joists where they lay on a beam or foundation). Also, keep adjacent holes at least 4 to 6 diameters away from other holes.
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  #3   IP: 68.37.48.49
Old April 18th, 2008, 10:16 AM
Logcabin1 Logcabin1 is offline
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Thanks for the quick response SuemarkP (Mark).

Quote:
In insulated cavities, the cables will be considered bundled. This limits you to 4 cables per hole before you have to derate and use a smaller breaker than normal.
I will limit to 4 cables per drilled hole. I hope that you are not saying that I am limited to 4 wires travelling within the same insulated cavity without derating because I was planning to use two runs of stackers within a in single cavity, one run traveling up each vertical member. If I should not do that I appreciate the catch....that would be a lot of work to redo...The plastic stackers I purchased say they can be used for 4 to 8 cables of size 12/2 or 14/2. Will I need to limit each stacker run to 4 cables or risk derating?

Quote:
Also, keep adjacent holes at least 4 to 6 diameters away from other holes.
I assume this 4 to 6 diameters rule for adjacent holes applies to holes in the top or bottom plates as well as joists/load bearing members. I had been planning to place one stacker on each side of the vertical cavity so I could have 4-8 wires on each side travelling from the crawl space up, through the first floor wall, through the second floor wall, to the ceiling of the second floor.
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  #4   IP: 76.104.172.149
Old April 18th, 2008, 07:57 PM
suemarkp suemarkp is offline
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The limit isn't on a cavity, it is the size of a bundle. A stacker prevents bundling, but the code still treats a hole as bundling if the wall is insulated. So 8 wires in an insulated wall on a stacker would be OK as long as you went through 2 holes. Having this on both sides of a stud cavity is OK too (in fact you could put a 2x4 across the stud cavity and have wires stapled all the way across the cavity. Just limit the entrance/exit to 4 cables per hole).

I'm not sure if the hole spacing rule applies to top plates. I'd keep the holes small to help (13/16 should be fine for four new romex in 12-2 and smaller).

Here's part of the exact code wording:
334.80: {part dealing with holes:} Where more than two NM cables containing two or more current-carrying conductors pass through the same opening in wood framing that is to be fire- or draft-stopped using thermal insulation, caulk, or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a) and the provisions of 310.15(A)(2), Exception, shall not apply.
{this won't apply if using stackers:} Where more than two NM cables containing two or more current-carrying conductors are installed in contact with thermal insulation without maintaining spacing between cables, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a).
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