basement floor joists


Old 04-24-06, 07:02 PM
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basement floor joists

Here's a boring but important question. What do folks consider the standard, and the best, practice for wiring nmb perpendicular to first floor joists in an unfinished basement, when the joists are not drilled. If you use conduit, please be specific as to what you do.

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Old 04-24-06, 07:44 PM
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Running board are one of the few options available if you don't want to drill the joists. Run a piece of 1 by 3,4 or 6 on the bottom of the joists and staple the wires to the bottom of the running board.
Old 04-24-06, 08:13 PM
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Originally Posted by BuffaloDIY
Love the pun!
Old 04-25-06, 07:38 AM
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is it actually against code to just staple to the bottoms of the joists in an unfinished basement?
Old 04-25-06, 08:09 AM
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Yes, if running perpendicular.
Old 04-25-06, 08:14 AM
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and a flat running board brings it into code? or do I need to raise the edges of the board, or enclose the wire?
Old 04-25-06, 08:18 AM
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A running broads make the installation code legal.
Old 04-26-06, 02:18 PM
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but is that the best solution?

Originally Posted by racraft
A running broads make the installation code legal.
But is that what you would do? Ok, it meets code, but that seems more exposed to potential damage than drilling the joists, plus makes it more difficult to ever install a ceiling. Of course, drilling the joists too much seems like an even worse idea.
Old 04-26-06, 05:20 PM
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If all the wires in that section of the basement were simply stapled...I'd staple another one. If all the existing wires were bored through the joists...I'd drill holes and make what I did look like what is there. Just seems common sense.

Don't you already have wires down there? If so, what method was done?

I thought one of the ideas of a 'running board' was to actually not just wire staple a wire to the underside of a board but to create nailing boards in such a way (boards on each side of the wire) that there is a channel for the wire, to reduce the odds of the wire being hit. I thought I read that in either this electrical forum or some other.


You said you can wire staple to the bottom of joists if running perpendicular. Are you indirectly saying then that you really can't if you are wire stapling along the bottom of a joist, in the direction the joist is going? If this is the case, why can't you? *I* always staple it up on the side of the joist, and this is probably proper. But I'm wondering why, if you can *cross* a joist with a wire...then why can't you simply run it along the bottom? Is it because the odds are greater of the running wire under the joist, of being pinched/hit somehow from below? It's always nice for people to understand if they *can't* do something as to the logical reason why they can't, IMO.
Old 04-26-06, 08:26 PM
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Just exactly how is drilling the joists a bad idea? Most houses are wired that way. The people who make lumber joists for a living have a few simple rules for drilling joists that if followed won't weaken the joists. People cutting joists for plumbing are what weaken the joists.

Rules are: (for JOISTS, walls are different)

1) no holes in lumber smaller than 2X6

2) no holes closer than 2" to the edge

3) no holes larger than 1/3 of the height of the joist (actual height, not common lumber size - a 2X8 isn't 8" high)

4) holes must be spaced 3 hole diameters apart minimum (2 inch holes would have 6 inches between them)

Given holes for wiring are usually 1/2 to 7/8 inch, there isn't much risk of screwing up a virgin floor joist because you drilled holes in it for wiring. I drill joists all the time and in fact charge a LOT more if I have to deal with a homeowner who won't let me.

The National Electrical Code prohibits fastening anything smaller than a cable with 3-#8 wires to the bottom of a joist, perpendicular or otherwise. Reasons are many but include preventing damage from any number of things. Most AHJs will require running board mounted cable be stapled to the side of the board, in most cases requiring a 2X4 be used, and will reject wire stapled to the bottom of a board which is essentially the same thing as fastening to the bottom of the joists and offers no protection. The code assumes you know where to put the cable on a running board because it isn't written for DIYers.

Boards used for protection in attics are placed beside wire fastened to rafters and other attic framing to prevent things from being stored on them or people stepping on them, kind of si,ilar to the "channel" idea.

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