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Thread: Drilling holes and running wire

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    Tom Nicelley is offline New Member
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    Drilling holes and running wire

    Can any one help me with a few questions;
    1. Are there any guidelines to follow when drilling thru studs, joists, rafters and such. What size hole (and number of holes) can I drill without having to worry about weakening the stud. Are there any stuctural members that I shouldn't drill through?

    2. How many wires (12-2 mostly) can I run together (meaning, in contact with each other)? I have an old laundry chute that could be handy in getting my wiring to the attic, but I'm unsure about running the wires for 8-10 circuits all throught the same space.

    Thanks,
    Tom

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    kactuskid's Avatar
    kactuskid is offline Master Journeyman
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    quote:Are there any guidelines to follow when drilling thru studs, joists, rafters and such.
    Yes, listed below are the requirements for both joist and studs:

    FLOOR JOISTS

    Holes: Do not bore holes closer than 2" from joist edges, nor make them larger than 1/3 the depth of the joist.
    Notches: Do not make notches inthe middle third of the span where the bending forces are greatest.
    Notches should be no deeper than 1/6 the depth of the joist. Notches at the end of the joist should be no deeper than 1/4 the depth. Limit the length of notches to 1/3 of the joist’s depth.

    WALL STUDS

    1” is the max diameter , we can have in 2 x 4 [3.5”] studs and avoid the 1/16” nailer plates due to the 1.25” NEC rule. (NEC rule: all wires must maintain a minimum of 1.25" from edge of stud on both sides) If you end up getting closer than this then install a metal nail plate across the studs edge. Three NM-B 12-2G ,Romex® will not require a hole larger than 1"..as 3/4" is a bit traumatic on the sheath, when pulling (3)size 12-2G NM cable.

    ¾” hole for (3) 14-2G

    1” hole for (3) 12-2G

    For structural (not electrical) reasons, keep your bored holes dead center top to bottom, and at least three inches apart (edge to edge). Don't drill through any trusses whats so ever.



    quote:How many wires (12-2 mostly) can I run together (meaning, in contact with each other)?
    Although derating requirements begin at a lower level, when using NM-B cable, it usually does not become an issue until you run more than four cables together (for more than 24 inches). This is a simplification of the actual rules (and hence isn't correct 100% of the time, but 99% is close enough). So, if you bundle 3-4 cables together you should be fine running 3-4 of these bundles up the chute.

    Before you start any work I would suggest that you buy a good book, Black and Deckers book on Homewiring is a good one and will give you lots of details you need to know concerning placement of switch boxs, receptacle boxs, lights, etc as there are specific rules. Also, any and all juction boxs must remain acessible at all times.

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    Tom Nicelley is offline New Member
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    Thanks Kactus!

    quoteon't drill through any trusses whats so ever.
    What about rafters?

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    kactuskid's Avatar
    kactuskid is offline Master Journeyman
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    Yes, rafters are fine, treat them the same as joist.

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    HayZee518 is offline Deity
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    On inside studs like next to doorways, invest in something called "stack-its." These plastic nail ons allow you to stack about 8 cables on the side of a stud. All cables are to be stapled within 12 inches of any box. The stack-its allow you to eliminate the staples IF you nail it within the twelve inches of a box. In Massachusetts I was able to drill an 1 1/2" hole approx center of a joist about a foot out from a cellar wall and insert about8 cables through it HOWEVER I had to de-rate the cable because of the number of wires through the hole.
    A 7/8" hole will accept two #12 cables through it. Use a 7/8" X 18" self feed auger. You'll save yourself a headache in drilling. ok, DO NOT drill through the bottom rail of any type of truss, floor truss or roof truss. The bottom rail is under a tremendous amount of stress when supporting a roof or floor. Drilling a hole through it will weaken it as the rail is already trying to tear itself apart.

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