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I'll begin by saying that I'm no electrician. I was just wondering about the following:

TLDR: Is it ok to have two 12/2 cables and a 10/3 cable going through the same 3/4" hole?

For a washer and dryer there are currently two blue boxes with two yellow cables, which I suspect to be 12/2 cables, going through a hole (through wood, but not a floor joist) maybe 3/4" wide. Turns out a gas dryer wasn't possible so I needed a larger wire, so I ran an orange 10/3 cable through the same hole as the 2 12/2 cables.

My question is whether or not this is OK? The reason I did this is because the ceiling is going to be boarded up and now is the time to do it. The 10/3 cable going to the panel has a drop ceiling so I am going to let the electrician handle the wiring of that (though for now I did just run it along the joists and to the panel).

The 10/3 cable is pretty thick so I did have to tug a little bit to get it through the hole, but it appeared to be undamaged and fine. I'll add by saying that the 10/3 and 12/2 cables are not running parallel once through the hole. In fact they diverge (something like below)

                              ^
                              |
                              |
                              |
                              |
                              |
                              |
                              |
                              |
                              |
                            12/2
                              v
<---------10/3 cable ------>  * 
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  • Just to make sure: this is all indoors, right? If it's indoors, it doesn't matter half as much as when it's outdoors.
    – Mast
    Oct 25, 2018 at 16:58
  • Those are called cables, not wires. Wires are the single things inside them, i.e. That are white, black, bare, etc. Oct 25, 2018 at 18:59

3 Answers 3

12

In the US, as far as the National Electrical Code is concerned, you can run three cables through a hole bored in a joist or rafter as long as you can run the cables without damaging them.

If the bored hole was longer than 24", you would have to observe the rules for bundling and do derating calculations - that is, figure out the diminished current carrying capacity of the cables. This would be very unusual in house construction, there are not many walls, beams, etc. that are 24" deep.

There may be local codes that apply in addition to or instead of the NEC - can't say what applies for your area.

Some people have their own rules about how many cables can go through a single bored hole. Sometimes these rules of thumb are pretty popular, and can be confused with actual code requirements, even by inspectors.

The safest thing to do in these situations is contact your local code enforcement department and ask. Of course, it's often a lot easier to drill another hole.

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  • In Knox County, Tn ( Knoxville ), we're allowed 2 wires per hole. Mixed gauge wires can be run thru the same hole if they are #10 or smaller. Again, that's specific to my location.
    – BillWeckel
    Oct 25, 2018 at 13:51
  • 7
    @BillWeckel you probably mean 2 cables per hole. If it were 2 wires, you wouldn't be able to run anything at all! Oct 25, 2018 at 18:15
  • Bundling or Conduit Derating won't impact 3 or fewer circuits of #10 or smaller. It also won't impact 4 or fewer circuits of #12 or smaller. Oct 25, 2018 at 18:17
  • @Harper You'd be correct. I don't use the term "cable" as I probably should. Cable to me means just that, cable wire, as in coaxial cable.
    – BillWeckel
    Oct 25, 2018 at 18:21
  • I'm not sure about NEC, but CEC (which is usually very similar) stipulates derating limits for greater than 24" of parallel runs in contact - I don't think the cables need to go through a 24" long hole for that to apply; even if they're just strapped together or run together across a wall (sharing holes in the studs) then derating applies if you exceed the maximum number of wires.
    – J...
    Oct 25, 2018 at 18:59
4

Assuming the 10/3 is certified for that use, it's legal, although "I did have to tug a little bit to get it through the hole" means it's a tight fit and I'm not sure the building inspector would like it, if the inspector ever sees it.

I'd just drill a new hole and be happy to not have to worry about it.

FWIW, not all 10/3 is legal to run for house wiring. For example, you can't use SJ or SJO.

2

Yes you can run a cable of #12 and a cable of #10 through the same hole.

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  • Would anything change if that area is going to be insulated? Any things to note in terms of fire safety? Oct 25, 2018 at 12:13
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    @TabethNkangoh - Most municipalities require you to seal bored holes with foam or other means to keep the ingratiate of fire protection of the stud. Oct 25, 2018 at 12:37
  • @RetiredMasterElectrician Thank you for the information! Oct 28, 2018 at 21:59

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