passing romex through floor joists


Old 09-19-00, 05:29 PM
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I am in the process of rewiring my house. I have read in a Basic wiring book that I have to drill a 5/8 hole throught the joists to pass romex through. My question is, is there a limit on how many cables I can pass through a hole in a floor joist? Can I drill a bigger hole and pass several cables through? I'm working with 14-2 & 12-2 romex.
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Old 09-19-00, 06:41 PM
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To preserve as much strength in the joist as you can, drill the smallest hole through which all the wires will fit, but don't cram them in too tightly. And drill the hole dead center in the joist (top to bottom). If you have a choice, drill the hole near one of the supported ends of the joist instead of in the middle of the run.

No place is it written that you need a 5/8" hole. You can go larger or smaller as your needs dictate.
Old 09-19-00, 09:39 PM
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What John told you is true, but he left out one detail. Drill the hole in the center of the stud. If there is less that 1-1/4" of wood from the hole to the edge of the stud, attach a metal plate on the edge of the stud to protect the wire. Certainly don't want to put a sheetrock screw or nail into a wire!
Old 09-20-00, 11:24 AM
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These guys are right as per the NEC about the 1 1/4" from the edge of the joists, but by the CABO 1 & 2 family dwelling book, you can drill a hole anywhere in the joist that you want as long as the hole does not come within 2" of the edge of the floor or ceiling joists, and the diameter does not exceed 1/3 the depth of the joist. A hole is no more than a knot in the board. Stay away from the very end of the joists, this will cause splitting of the joist.

Now notching is another ball game. YOu can notch a joist, but only on the compression [top] side of the joist, never on the tension [bottom] side of the joist. Cantelevered joists may not be notched unless with enegineering documents on the design and load factor. Now you can only notch a joist in the outside 1/3s of the joist, not in the middle of the joist. Your notch is limited in size to no more than 1/6th of the depth of the joist.

The above is for repetitive members which are load bearing. It does not apply to non bearing wall studs. A bearing or outside wall stud may not be bored with a hole exceeding 25% of its width.

I agree that their is no limit to the smallness or the largeness of the hole you drill by the NEC but you might check that you are not violating the Building Codes. Even though you are acting as an electrician you are responsible for the notches and holes that you drill and under the authority of the building Code.

The previous replies are right about not making too tight but by Code you could stuff just short of causing damage to the wire. The NEC does limit the number of Romexes to be cabled in repetitive structural members to 24" before you come under the conductor ampacity deration charts found in 310-15-b-6. Just make sure that air is allowed between the Romexes between the joists so the conductors can cool both in between the joists and out the ends of your drilled holes, to avoid hazards due to the conductors heating each other.

Good Luck

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