Damn I hate this gettin' old

NEC 300.4

You've probably forgotten more than I know. So, I would just suggest you ask the local building codes people or inspector, as this is a way to meet him/them and let em know you intend to do it right. They like those kinds of builders. I'm in the middle of an addition, and I've called mine about six times so far. He said he would rather a phone call than declining approval because someone just didn't get a simple but important item right. I live in a small town. Things may be different where you are. Even though there are national standards, sometimes those little localities can and do have their weird ways of doing things.

Steve

We don't have inspectors here. I'm so far out in the sticks we get our email by UPS. I'm just wanting to follow the code.

Thanks. Greatly appreciated.

You don't live in Toquerville, Utah, too, do you? Same thing here. No house delivery of mail. Everyone has to go to the post office. UPS goes to post office. But the inspector is a nice guy, and if you approach him right, he'll point you AWAY from the cliffs.

Steve

Sorry RBM but 300.4 does not answer my question. In case I did not explain my question I offer it again. Example: I drill a 3/4" hole in the studs (they are 2X6s). How many 12/2 insulated cables can I run through the hole? I know I can NOT run a 12/2 and a 10/2 through the same hole, but I have occasion to run more than one cable through a hole. In fact there is one place that I would like to run 5 or 6 cables through a larger hole in sill plate that would be above the level of a suspended ceiling. Someone said that running too many wires through one hole, or parallel along a joist might cause too much heat buildup. But, I can not find anything in that regard in my 2005 NEC. Of course, I've not yet read it cover to cover.

I don't know of any limit listed in the NEC

JC wrote: ...

As many as will fit comfortably -- there's no code specification other than the "workmanlike" clause that I'm aware of.

What makes you think that? Absolutely no reason not to.

...

You haven't found it because it isn't there.

The referenced "someone" is blowing smoke.

Put whatever fits in the hole comfortably -- I'd try to leave a fair amount of "slop" rather than tightly packed certainly, but it's not a code restriction.

You could be ultra-conservative and consider the same fill ratio as a conduit but that would be overkill. For a large bundle I would prefer several smaller holes rather than the one big one as well, but that would be for structural reasons rather than electrical...

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Thanks again. I appreciate your response.

I believe I read that in article 314 of the NEC.

If you pounded the code hard enough you might say this was a nipple and you use the 60% fill rule. I believe that is a stretch but it might not be a bad guideline.

I thought about that but after some research and reading I got the impression that heat buildup was a "result" of the conduit material rather than the current. I know, it didn't make sense to me either.

PS: I believe I have found a starting point that will lead me to what I want to know. It is 310.10 including the FPNs.

The potential for heat buildup is a combination of both current and conduit. The current is required for the heat source; the conduit reduces cooling by restricting air flow around the cable(s) relative to open air.

In a short hole the thickness of a 2x, there's not enough length in the hole to be such a restrictive air flow as in a length of conduit so the fill rule would be somewhat conservative.

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Could I suggest ONCE AGAIN to merely call the inspector?

Or are you having too much fun here?

Steve

For those of you that are interested:

The best reference I have found seems to be NEC article 310.16 regarding the ampacity of wire. There are charts and footnotes indicating that one must derate bundled cables. One reference is to THHN wire with a 90 degree Celsius rating showing that bundled cable with 10 to 20 current-carrying conductors should be derated at the rate of 50%. The chart shows these conductors carrying capability to be 30Amps, thus when bundled in a group between 10 to 20 current carrying conductors the circuits should be derated to 15Amps. This is for 12/2 wire. The derating factors are 80% for 4 to 6 conductors and 70% for 7 to 9.

Case closed.

"JC" wrote

So, how many wires can you put through a hole, then?

Steve

Depends on the conductor(aluminum, copper clad or copper) and the rating of the wire (60, 75 or 90). For my application, between 10 and 20 current carrying conductors of THHN 12/2 can be bundled if you derate the breakers to 15 amps.

whoosh .......................!

sigh ..............................