My main electrical circuit breaker panel is on one end of our unfinished basement. I need to run 2 circuits to the far end of the basement. Normally I would mount these wires on the center beam that supports the home and runs down the center of the house. Since there is no more space left on that center beam, I would like to route #12 type NM wire through my basement ceiling by drilling suitable holes in the floor joists.

Is this legal and can I put 2 wires in one set of holes?

  • Do you have a finished ceiling in your basement?
    – Niall C.
    Commented Oct 2, 2014 at 17:13
  • Another alternative is to nail running boards (1x2, 1x3) to the joist bottoms, and then staple the NM to it. Although, future finishing of the basement then becomes problematic. Commented Oct 2, 2014 at 17:44

2 Answers 2


The general guidelines:

  • Don't notch a joist. (it's legal under the correct circumstances, but don't consider it until you have no other choice.)
  • Don't drill a joist near the ends. (how near is near? Stick to the middle third and be safe. )
  • Only drill on the center-line of the joist. (This is the area under least stress).
  • keep your holes less than 1/3 the height of the joist. A 3/4 inch hole for romex is fine under almost any circumstances.

These aren't the rules, these are a set of guidelines more restrictive than the rules, that you can quickly and easily work with in the field. If you want to work outside these guidelines, then consult the local building code.


Are you sure the center beam is full? You can stack romex, though derating rules apply. However, as most circuits are already derated, adding two more via stacking romex clamps might be ok.

This page of the rulebook applies, at least in Canada. http://www.dslreports.com/speak/slideshow/24708984?c=1575722&ret=64urlL2ZvcnVtL3IyNDcwNjI1My1CdW5kbGluZy1tdWx0aXBsZS1yb21leC0

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.