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Height of NM Cable In Walls??

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  • Height of NM Cable In Walls??

    Is there an actual height that you must run cable in a wall? My newest B&D DIY book says I might fail inspection unless I stick with 20" above floor. I sure hope not! Makes no sense to me. PITA for insulation for one thing. i've always drilled holes about 3" & 5" above plate and put receptacle boxes at about 14" high. But those weren't inspected situations.

    ALSO - why is the number of NM cable per hole such a vague, controversial subject. Can't they clean it up? Inside walls, Insulated walls. TJI's have huge 1-1/2" holes vs solid lumber. Derating of cables - what a bunch of crap. Based on that every house I've ever touched is on the verge of burning to ground & I really don't beleive that will happen.

  • #2
    Re: Height of NM Cable In Walls??

    First, I am not an electrical engineer, but have wired quite a few homes in the past.

    I do not know of a specific NEC Code that addresses this. However, the wire must be secured within 12" of a box.

    What I have always done is used my hammer as a "quick" height guide for my boxes and just held my right angle drill at arms length around my waistline and begin drilling studs.

    Beware that there may local codes above and beyone the NEC in your jurisdiction.

    Regards,

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    • #3
      Re: Height of NM Cable In Walls??

      I'm not sure on all the code on this one.

      In practice you generally need to stay over 20 inches to make things work. It is a bad idea to run on the bottom 6 inches because you risk getting your wires hit by drywall screws and nails from the baseboard. Your outlets are set at 16 or 18 on center. So you want to the wire to be at least six inches above or below a box so it can make a smooth bend into the box and have a staple securing it within 8 inches of the box. So if you go below 20 inches you have a lot less room to do what you need.

      The limitation on nonmetallic from my understanding only applies to conductors coming through above the service panel which are limited to 2 per hole. So you could have 10 conductors go up through a total of 5 holes from the panel beyond that the restriction doesn't apply so they could all hit the first floor turn 90degrees in the wall and go across in a single hole. Doesn't make much sense to me but thats how it is.

      Wires can not be within an inch or the surface without additional protection. This is to prevent drywall screws from penetrating the wire. If you drill on center with a bit larger than 3/4 it is possible for your wires to be within an inch of the finished surface. Any place your wires are within that inch it is acceptable to use additional protection such as a nail plate.

      For residential we drill around each room with a 7/8ths bit using a right angle drill at waist level. Go higher for doorways and lower fro windows. Looks more professional if the same guy does all the drilling because not everyones waist is the same height.

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      • #4
        Re: Height of NM Cable In Walls??

        Like it was said, their is no code that specifies a height for running romex. That is to say no code in the NEC, you code perhaps have a state or local code that does specify.

        Also their is no code in the NEC that specifies a limited number of wires in a bored hole. It does not matter where the holes are, their is no code that limits the number. Again, you could have a state or local code that does specify a limited number.

        Also as it was said, you can not have wires with-in 1 1/4" of the edge of the framing member you are going through. If you do have wires closer, the code specifies a 1/16" nail protection plate.

        Jeff
        Last edited by piette; 01-19-2008, 11:53 PM.

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        • #5
          Re: Height of NM Cable In Walls??

          While those were all valid points, you should also remember that running multiple (more then 2 wires) through a hole that is to be firecaulked requires de-rating of the wires - Article 334.80 of the 2005 NEC. Also keep in mind that stuffing a hole that is 7/8" round with multiple wires, the continous pulling of wires over other wires can cause burn or wear through the outter nm layer and inner layers. Just because there is room through a hole doesn't always mean to stuff it as much as possible. Pulling wires may seem easy, but like all trades, it's best left to a professional.

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