Help me out here folks. Awhile back someone posted a message about how many
wires(cables) you could run through one hole in a joist or stud. Someone
even posted the article number and I printed it out because I am running
wires for a house I'm building. Well, I've lost the printout and now I can't
find the post. I even went over to my super duper newsreader and searched
through 154000 posts and could not find it.
I'd sure appreciate it if someone could let me know where to find that
information in the 2005 NEC. I'm almost positive it's in the 314s.
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. <G>
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
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...
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. <G>
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
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.
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.
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.
Seems that is what has been suggested to you...repeatedly. The bottom
line is that no matter how well you know the code, how many cites you
can come up with, the inspector is the one who has to be satisfied.
Right or wrong his ruling is what is going to allow you to proceed or
not as the case may be.
A bunch of wires going through a hole on 2x stock is not the same as bundleing.
If there are airpassages through a collection of loose wire betreen the
studs/joists, heat dissapation increases. Heat with the hole will be conducted
to the wire that can dissapate heat.
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