ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

anybody know whether or not running wire on the bottom of floor joists in a basement is acceptable, if your going to put up a tbar ceiling. i have a house which only has 2x8 floor joist's and i would like not to drill through them. to the best of my knowledge the answer is no, but maybe somebody know's the codebook better than i do. or know's the inspector will allow it under these circumstances. i'm in ontario by the way

12-514(b) says you can if the wire is protected from mechanical injury. Above the ceiling is okay, but isn't okay until the ceiling is installed. The traditional protection is a running board beside the wires or running the wires on the side of the beam.

If you keep the holes in the middle of the joist, it won't weaken the joists. The rule refers to Appendix G that has a cross reference to the National Building Code 9.23.5 about drilling joists. Last time I looked, I couldn't even find a carpenter with a copy of the National Building Code and mine is from 1985. Perhaps someone has a more up-to-date copy. In the meantime, the rule WAS that the hole had to be 50mm from the edge and have a diameter less than 1/4 the depth of the joist.

Don't drill trusses.

Without approval by the structural engineer. Greg you can drill some trusses but only in very specific areas, of certain maximum diameter, etc. But drill it in the wrong place and lots of trusses need to be completely replaced.
That said, your advice is still good as getting it wrong or without the engineers approval can be very expensive.

The typical I-beam truss that I've encountered has factory provided KOs that blow out with a light tap of a hammer.

The worst place to open up a large hole in manufactured trusses is at the ends. That's where the stress is the greatest.

Manufactured beams are another story altogether...

We never penetrate them -- and the factory does not provide any KOs, either.

this is an old house guys no engineered trusses here. the original floor joists are just 2x6s thats why i dont want to drill at all.

floor joists or trusses....what is it. Is there not a difference? Never drill a truss as far as i'm concerned.

some of the replys are refering to the engineered trusses made out of chipboard and 2x2s this is an old house with 2x6 floor joists. i'm hoping to not have to drill holes in them if they were 2x 10s as they should have been then no problem.

I’m in the US so not familiar with the CEC, but in basements and crawl spaces of older buildings with under sized joists we used to shim and screw one or two 1X running boards across to the bottom of the joists and staple the wiring to that. The width of the boards was determined by the number of wires to be run. We would cut them at various angles to go around corners or change direction to follow the room or area. It looked really neat and is allowed to be done this way in the NEC. Hopefully there is enough ceiling height to allow the T-bar ceiling track to mount just below this level.
If there is not enough room to use the running boards, I would ask your inspector if he will allow you to mount the wires directly to the bottom of the joists and protect them with 1X strips on each side. This isn’t really ideal as far as the NEC is concerned, but once the T-bar ceiling is up, IMO it shouldn’t be much of an issue.