ECN Forum Forums Code Related Discussion NEC & other Code issues Wires per hole??

an oldie, but goodie....

how many wires can i put in a hole?

assume rx or mc thru wood joists here....

As many as will fit in the hole. Remember that the hole must comply with 300-4 and must not destroy the structural strength of the framing member. This assumes that the cables will NOT be tightly bundled between framing members.
Don(resqcapt19)

Sparky,
That is a good One.

That would Depend On the size of the hole.We would still consider art 300-4 in application of this method.

Wayne

I've mentioned before in another thread (there ought to be a law) that I'd like to see a requirement for bored-hole fill similar to pipe fill. I use it as a rule of thumb when dealing with larger cable, (2" for 4/0 SE. 1-1/4" for #2 SE, etc.)

As far as #14 and #12 NM Cable, I go no less than 3/4" , usually 1".

Virgil;
yes you did, and it's worthy of a thread's consideration.

to add to the Q,
what would qualify as 'bundled'

A bored hole through a 2"X4" seems to have a lot in common with a nipple especially if the wall is insulated too.

Do you mean that some people don't make a separate hole for each cable on minimum one-diameter spacings?

If I did that I'd be making $3 an hour on bid jobs... but for cost-plus, that's OK!

Please don't tell me it's code to do so...is it? It'd make swiss cheese out of the homes I've wired. One hole in the center of the joist/stud/plate makes for less structural degradation.

Bundled cable derating is one of the most ignored codes around here to this day... heck I'm guilty of it I suppose...

Of course it is legal to do so...


I can't speak to structural degradation, but I can't imagine how Swiss cheese is worse than a big whole. My gut feeling is that a bunch of half inch holes a half inch apart cause less weakening than a single large hole.

I've pulled NM out of joists where the holes were sized and shaped almost exactly to the oval shape of the cable.

Of course, 12-3-G fills a round hole nicely.

Let's just say that I lean toward Swiss cheese as the preferable way. I think so long as I'm leaving 60% there, it's structurally safe.
If you are making a single hole up to 1.5", I wouldn't object, especially if you are restoring it with steel.

Perhaps you need a faster drill or a sharper bit.

It's easier to trace wires through Swiss cheese than in a bundle, but a little harder to protect with plates.

No derating in Swiss cheese...

Myself,
There are probably few people outside of our trade that appreciate our's as having any asthetic value, but i just like a neat job.

if i do a complete building, i like to wire for expansion. So when it comes to wood i usually arrange via chalkline 3 to 4 1 1/2" or 2" runs back to the panel, possibly more closer to the panel. First i ask the carpenters, they are responsible for load bearing, etc. The time i take to do this pays off. I have found a self-feed and right angle works best, having all holes at an angle tends to work the wires thru hard.

All the runs are pulled easily, they occupy on average 1/3 to maybe 1/2 of the hole diameter, always room for that future sparky.

All runs starting from the panel fan out neatly, which looks good as an end result.

I believe the derating factor for 1" holes dead center of the framing member to have about a 4% decrease in structural integrity. 1/2" holes would be 3%. If they are not dead center, then up to 30% derating of the load carrying ability of the member must be assumed. I was told this by a P.E. I worked for, so I can't back up its accuracy. So it's kinda moot.

I guess the important thing is to have them dead center.

I don't put more than three cables in one hole under any circumstances, just a rule of thumb.

I should mention that I tend to "exaggerate for clarity" if that makes any sense. In today's sensationalized world, sometimes it's hard to get a point across without going to the extreme!

[This message has been edited by sparky66wv (edited 05-14-2001).]