NM cable through joist holes- general consensus?

[s14kev]

Quick one which seems to have varying responses. In a basement garage I'm running NM cable (14-2 and 12-2 most commonly) for lights and power. I generally try to use the pre-existing drilled holes in joists which already have NM cable for the remainder of the home. How many NM cables are allowed per hole (generally 1" or 7/8" holes). Responses vary from as many as will fit without physical damage (ie. they can be pulled through fairly easily) to only 1 cable per hole. I think 1-2 cables is silly as drilling hundreds of new joist holes is not ideal for structural integrity.

Home was wired in the 80's and done well but some is clearly not to code (eg. no running boards for some 12-2 cable stapled directly to bottom of joists).

 

[ard]

personally I just stuff them through..... If you have to force it, thats too many.

 

[Innovate1]

That's really a question for the AHJ and their interpretation is going to vary. When I built this place I think they wanted to see no more than half full or something like that. Seems like you should be safe with conduit fill percentage which is 40% and you could use that to support the position since it isn't as confining as conduit.

 

[Stuart in MN]

This discussion on the Mike Holt forum is from 2012, so it predates the current 2017 NEC, but it shows some of the gyrations you need to go through to come up with an answer: https://forums.mikeholt.com/threads/number-of-nm-cables-through-hole.94202/


(note: the original poster didn't give a location, so I'm assuming they are in the US and need to follow the 2017 NEC.)

 

[Kevin Essiambre]

I'm in ontario canada. We are permitted to run 3 two conductor cables through a 7/8" hole without de-rating for a 15 or 20 amp circuit.

More than 3 on our code becomes a hassle.

I would stick to 3 per hole.

Sent from my new phone. Autocorrect may have changed stuff.

 

[s14kev]

This discussion on the Mike Holt forum is from 2012, so it predates the current 2017 NEC, but it shows some of the gyrations you need to go through to come up with an answer: https://forums.mikeholt.com/threads/number-of-nm-cables-through-hole.94202/


(note: the original poster didn't give a location, so I'm assuming they are in the US and need to follow the 2017 NEC.)

I'm in TN. That thread in the Mike Holt forum only adds more confusion

 

[sberry]

As a matter of good practice 3 and in some cases 4, 4 for a short distance is allowed, 24 inches.

 

[Stuart in MN]

I'm in TN. That thread in the Mike Holt forum only adds more confusion

That was kind of my point. Unfortunately there's not a cut and dried answer.

 

[PedroEvo]

I'm in ontario canada. We are permitted to run 3 two conductor cables through a 7/8" hole without de-rating for a 15 or 20 amp circuit.

More than 3 on our code becomes a hassle.

I would stick to 3 per hole.

Sent from my new phone. Autocorrect may have changed stuff.

1000%


Sent from my iPhone using Garage Journal

 

[Stuart in MN]

The original poster is in Tennessee, so Canadian rules don't apply.

 

[canbug]

If you are just pulling through joists, there is no derating of the conductors because the distance together is so short. Inspectors don't even look at it but a quick call to your local Electrical Inspection Department will give you the definitive answer for your region.
Rule of thumb is if it pulls easily no matter the number of wires, your good to go.

Tim.

 

[Innovate1]

The Mike Holt link goes into all the gory details but lots of difference of opinions there so very confusing and I doubt many inspectors get that deep. As I said before you should just ask the AHJ (inspector) what he considers ok. Most will give you a straight forward answer. Not likely in my experience but a few may be jerks and say if you are wiring the place you should know what you are doing. Most will keep it simple such as no more than a certain number (although it should vary with hole size) or not crowded or some such.

I just looked at some of mine that is exposed. I was just using the 1.4" holes that are prepunched and can be knocked out in the I joists wherever I could. I have up to 6 through holes near the panel and a few cables are #10 that are bigger than 12-2. A few of them are pretty full but not packed tight.

Only sure way to know is to ask the AHJ.

 

[Innovate1]

If you are getting this inspected they may want you to correct the other issues you mention with the existing wiring too.

 

[checkthisout]

Quick one which seems to have varying responses. In a basement garage I'm running NM cable (14-2 and 12-2 most commonly) for lights and power. I generally try to use the pre-existing drilled holes in joists which already have NM cable for the remainder of the home. How many NM cables are allowed per hole (generally 1" or 7/8" holes). Responses vary from as many as will fit without physical damage (ie. they can be pulled through fairly easily) to only 1 cable per hole. I think 1-2 cables is silly as drilling hundreds of new joist holes is not ideal for structural integrity.

Home was wired in the 80's and done well but some is clearly not to code (eg. no running boards for some 12-2 cable stapled directly to bottom of joists).

The rule is 9 current carrying conductors per hole without derating. This means 4 NM (2 conductor) cables per hole without de-rating. The rule for hole size is null. As long as you can pull the wires through the holes without damage and and the holes are the correct clearance from the outsides of the stud then you're good to do.

 

[checkthisout]

If you are just pulling through joists, there is no derating of the conductors because the distance together is so short. Inspectors don't even look at it but a quick call to your local Electrical Inspection Department will give you the definitive answer for your region.
Rule of thumb is if it pulls easily no matter the number of wires, your good to go.

Tim.

If the joists will have insulation in them, that's considered bundled.