Wiring across or through floor joists

Old 01-30-03, 04:34 PM
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Wiring across or through floor joists

I have to run five circuits from my circuit box in one corner of my basement to my addition, which is just off the other corner of my basement. Where I have to cross joists, can I staple the wires up against the joist, or should I drill through and run thru holes?

If I do run thru holes (here or anywhere else), is it one wire per hole, or can you put more than one through a single hole?

Thanks in advance...

Old 01-30-03, 05:20 PM
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If you think you may later finish the basement, you'd do better to bore the holes. Bore the holes dead center in the joist (top to bottom) and not in the middle fifth of the span, nor in the quarter of the span nearest a supported end (e.g., with a twenty foot span, drill the holes no closer than 5 feet and no farther than 8 feet from either end). You can put more than one wire through a hole. But if you need more than three, I'd use multiple holes (at least three inches apart) with no more than three cables through each hole. Use the smallest hole through which the wires will fit comfortably (without risking damage to the sheathing).

Otherwise, you can run them along the bottom of the joists if you install a "running board", which can be as simple as a 1x2 nailed to the bottom of the joists. Staple the cable to the 1x2. I'd run it close to and parallel with some other obstruction (e.g., a duct or pipe) that will already have to be dealt with if the basement is finished later. To run multiple cables, use a larger running board (1x3, 1x4, 1x5, etc.).
Old 01-31-03, 07:58 AM
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They changed the local code in a suburb of Buffalo as of Jan 1 to "center 2/3" of the joist, and not within 2 feet of a support.

I heard it's because much of the new construction of larger homes in that area uses OSB beams as joists.
Old 02-03-03, 06:45 PM
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You can drill small holes in the middle of a joist anywhere along its length. It's NOTCHING that has restrictions on depth, width, not in middle third of the length, etc. See Residential Code of New York State section R502.8 (Exact same wording and illustration as section R502.8 in the International Residential Code for One and Two Family Dwellings). Aside from code requirements, this makes sense. The top of the joist is usually in compression and the bottom is in tension, while the middle isn't really under much strain.
Old 02-04-03, 07:43 PM
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Use a 24 inch auger bit in a 1/2 inch drilll. The best place is in the middle of the joist vertically. This is the neutral plane and the joist is in neither compresion nor tension at this point. It actually varies with the span position, but for small hole (less than 3/4 inch in a 10 inch height) does not matter much. If you drill every other joist from the opposite side, pulling cable is a little easier.

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