Guys need some quick help. How many romex wires can be in one 1 1/2 in hole in a wood top plate. I have a circuit panel inside a garage, new construction, with the hole at the top plate completely stuffed with 12/2 romex. I have attempted to add the picture, but don’t think it went through.
There is no limit. Some might say this is bundling, but I seriously doubt the wires are tightly grouped together for more than 24" in this instance.
thanks
As many as you can without damaging the jackets of the cables.
Spock: An illogical approach to electricity does have its advantages on occasion, Captain. :mrgreen:
You need to address derating issues when stuffing holes with cables.
tom
Care to support this claim?
Electrical Myth #47
You only need to derate if they stuff insulation in that hole 334.80. Do you have an energy code?
Not around here(NE Pa) I’ve been getting word from other electricians that fire inspectors are looking at not just top and bottom plates, but studs and joists. So when drilling hole and running wires, we break our runs up to minimize bundling, and how many #14’s and #12’s go through holes. We can get the order to fire caulk every hole, as they want. The Myth is that this is coming from California, I think it’s being lobbied by fire caulk makers. 
tom
Hey, I’m in PA too, and we all work out of the same set of rules. Bundling is not bundling until it’s for 24 inches or more. I’d appeal the red tag for multiple cables in a top or bottom plate in a heartbeat, and I’d have to win. The code text is very clear on that matter.
So is 90.4
So now just incase, I drill an extra hole everytime I get to 9 cc’s 14# and 12# and 6 for #10.
tom
90.4 isn’t permission to make stuff up.
You better beileve it!
The rule about derating cables through firestopped holes is new in 2005. This is ONLY for holes that are (or to be) firestopped.
So here again we are caught with the “when was the hosue built” problem and* “what code was it under when it was built”*.
Good points Speedy,
I’m addressing both worse case, if I get hounded by the fire inspector, and then by the electrical inspector, so commenting specific on my work.
However, the OP says New Construction, Russel is in Texas (they adopted the 2005 NEC about the same time we [Pa]), through a TOP Plate(so fire caulking[or other method] should be required if not by fire codes, the NEC implied), so 334.80 seems to apply here(in this post).
Seems the term “bundling” is open for discussion, it was mentioned a distance was required, but I was instructed by an inspector, the actual text for derating[related 310] is ‘bundled more than 24"’ if just ‘bundled’ is mentioned, no distance is implied. So any bundling is bundling [related to 334], therefore bound by a hole in wood is bundling.
tom
Ironically enough when you do get involved with the derating of the NM Cable for the examples you all are giving…and end up using 90 degree for derating it in most cases with 14 AWG and 12 AWG wont effect the ampacity.
Basically if we had (4) 14-2 NM Cables thru the firestop…(4) current carry conductors so apply 310.15(b)(2)(a) and 80% would still be fine…for 15A breaker…without getting too detailed in it…so really it is not nearly an issue as other factors…
For example…how many inspectors make electricians adjust the ampacity in areas where the attics get VERY HOT…again without doing the math would it matter much on smaller NM Cable…probably not.
Where more than two NM cables containing two or
more current-carrying conductors are bundled together and
pass through wood framing that is to be fire- or draftstopped
using thermal insulation or sealing foam, the allowable
ampacity of each conductor shall be adjusted in
accordance with Table 310.15(B)(2)(a).
Now…I really dont like how this is written…I had one argument a 14-2 contains only (1) current carry conductor and because how that reads it says…more than (2) NM Cables containing two or more current-carry conductors…but a 14-2 only has (1) current carry conductor…lol…I know…I know…but thats how debates get going.
In residential you really don’t have that much firestopping, it is mostly draft stopping. That is why I asked about your “energy code”. Generally the only fire rated assembly in R3 is a ceiling over a garage if there is living space above. Some local codes also want 1hr between a garage and the rooms next to it but that is not how the IRC/Florida Building Codes read. It is assumed draft stopping also slows the spread of fire products and thus does slow the spread of fire. If this is that spray in foam YMMV since it is flammable. They are taking a long hard look at that in Florida as we speak.
For the purposes of 334.80 it is a distinction without a difference. If the hole has insulation in it you must look at derating. It really just gets back to the original question. How many wires are in one hole. This pretty much tells the installer not to jam all the Romex in one big hole. Drill several smaller ones.
Here in Pima County, Arizona fire caulking is now required on all top plate penetrations for residential. And yes, de rating in these holes is being enforced. We are buying smaller bits and drilling more holes.