I want to run a number of new circuits onto a single long wall. There
will be 6 or 7 circuits total on a wall that's about 50'. They will
all use 12/2 from 20A breakers and feed new 20A receptacles.
Right now I only know of one good path from the basement to the 2nd
floor. However, from what I've read it seems I can't just run all
these cables in one big bundle. How much separation do I need between
them? How many can I bundle without heat being an issue?
Once into the attic (thankfully I have some low attic access to the
back of this long wall) I can come up a roof joist and then down a
stud on the back of this wall and then fan out in the appropriate
direction. 6 of the 7 will head in one direction though. So as I run
through the studs, I don't want to drill 6 holes in each one. How
many can I bundle here? What's the separation requirement?
On Wed, 12 Dec 2007 08:40:42 -0800 (PST), firstname.lastname@example.org wrote:
Just don't tie them together so the air can circulate around them. In
inaccessible areas it is OK to fish them without securing in place.
This is one of those times when neatness is not a good thing. If the
cables are wrinkled and twisted they won't lay tight together
So all the wiring will pass through the attic? Have you considered just putting
a subpanel in the
attic? Then there's only 1 wire to run to the main panel.
We did that when adding a 2nd floor to our house, it made wiring the 2nd floor
Curious here. When I remodeled I didn't pay any attention to the
number through one hole, figuring if they fit without cramming it was
alright. The limiting factor to me was not weakening the stud/plate
thus my largest hole was 3/4" and I probably have 3 running through a
The only limits I am aware of:
if they are going through wood framing that is required to be fire or
draft stopped with insulation or foam, derating factors apply if there
are more than 2 cables (NEC 3334.80).
if they are stacked or bundled together for more than 24" derating
factors apply (NEC 310.15-B-2-a). (separate the cables as gfretwell
Speaking of insulation, the wall that will get all these outlets does
have insulation (fiberglass) between each of the studs (its backside
is into an attic space). From what I can tell, the original wiring
was wired over the top of the insulation (its very thin, so fits
between the wallboard and the middle of the stud where the hole and
cable is). Since then a previous homeowner laid thicker pink
fiberglass insulation against the wall between the studs. Is there
any issue with these wires being that close to insulation? I would
intend to run the new wires like the old ones (between the two layers
I have not heard of problems with old cables in insulation - someone
else might have.
Romex for many years has had 90 degree C insulation. A major reason is
it is often buried in insulation. The 90 degree stuff is NM-B - should
be the only Romex available now.
You aren't supposed to insulate around the old cloth covered "knob and
tube" wiring, but there are no problems insulating around modern romex
cables. Wires run through insulated walls all the time.
As for the temperature ratings on NM type cables, that mostly pertains to
the heat buildup around light fixtures. The newer NM-B cable has a higher
temperature rating than the regular old NM. I've opened up old light
fixtures that used regular NM cable, and the insulation was dry, brittle,
and cracking away leaving exposed wires.
In any case, buy new cables today and you'll get the higher temperature
rated NM-B (doesn't hurt to check the printing on the cable though). Either
type will be fine in insulation though.
The main concern with bundling cables is heat build-up. My inspector said I
could run two cables through a single hole at the breaker panel, so I
assume it would be OK to run two through holes in a stud as well. However,
from an installation standpoint, I still prefer to drill separate holes for
each cable. It will be a lot easier to pull cables that way.
It's really not that difficult to drill holes in studs, especially if you
get a self-feed auger bit. And, you're probably not running all six
circuits to the end of the long wall, so the number of holes needed will
decrease as you go. Regardless of the size of hole you drill, to avoid
weakening the studs, you should have at least 2" between each hole. Go
farther if you have the space. I would use a 5/8" bit for the 12/2 cable,
and drill six holes in each stud. Two smaller holes spaced apart should
weaken the stud less than one larger hole.
When I wired our house, I had to run numerous cables up from the breaker
panel, along a 25 foot wall, and then branch off to various parts of the
house. In some places, I have as many as 10 cables running through studs.
I've uploaded a couple of pictures to:
From experience with this, the best place to run cables from the
basement to the attic is next to the plumbing vent pipe. There's
usually quite a bit of room in there and no drilling is needed.
I agree with the guy that said to put a separate sub panel up there.
While the cost of the heavier wire and the additional box is an extra
expense, it might be the same as running all that 12/2, considering
the price of wire these days.
This is the way I'm leaning now. Run 6/3 from a 60A 240v breaker in
the main panel to a sub main lugs panel on the 2nd floor, and use 12/2
to run 6-7 20A 120v circuits from that subpanel. I expect my max
simultaneous load to be around 70A at 120v.
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