How Many Wires Can Fit in Each Hole?

When roughing in for new residential wall rough, does it really matter how many pieces of NM cable we put into each hole drilled thru the studs? In the latest episode of Electrician U, Dustin answers this question and brings to light some of the code articles associated with it.

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The very first thing to mention would be your local AHJ. The Authority Having Jurisdiction. That usually is your local inspector. They have the final say on approving your installation or not, so it makes sense to see what they are requiring, before just going out and doing! Some inspectors like no more than a couple, while some allow you three, etc. The last thing you want to do is rough in an entire house only to find out that the inspector won’t pass your wall rough, and you must do a bunch of rework! Trust me here, its no fun and can be quite aggravating.
The NEC doesn’t specifically talk about how many wires you can install in a given size hole in a stud. And that also makes sense when you think of how many different sizes of holes you could drill in a stud. What the NEC DOES talk about that is related to the topic is cable bundling. If you were to install a bunch of NM cables together thru the wood studs and tie wrap them every few feet, it may look nice and neat but there are a few issues with an installation like that. The first would be heat dissipation. With so many cables that close together, they cannot dissipate the heat generated by the flow of current in them. This can be a point of contention to some of us. The likelihood of ALL those NM cables being run at FULL CAPACITY at the same time is pretty low, so is the need to dissipate a TON of heat really that important?
The more likely reason the NEC doesn’t allow us to bundle (without derating) is due to capacitive coupling. When you have two conductors run next to one another and an air gap in between them, you have the ability to build up capacitance. Capacitance is the ability of a component or circuit to collect and store energy in the form of an electrical charge. So, the theory here is the more space you provide between those conductors, the more you can reduce the effects of that capacitance. That capacitance CAN impede current flow in the conductors. If you had 10 cables bundled together, with 10 different amounts of current flow running thru them, all that capacitance can have a large adverse effect on the current flow. Table 310.15(C)(1) of the NEC is where we derive the values that we must derate our conductors when we install several of them together in a conduit or thru the wood studs of a wall, or things like that. The NEC doesn’t tell us that we CAN’T install many cables closely together, just that when we do, we may have to adjust our conductors to be able to carry less amperage than standard wire sizes normally allow.
So, in a nutshell, NO, the NEC doesn’t tell us how many conductors we can put in any given size hole in a stud. The larger the hole, the more cables you can fit in there. And the larger the hole, the less chance of you damaging the NM cable when pulling it thru the hole drilled in the studs. In fact, Article 300.4(A)(1) of the NEC tells us that if we drill holes in the studs for NM cable, that we cannot be closer than 1-1/4” to the nearest edge of the wood member. Bottom line is to plan your work and install the cables without damaging them.

[Hunter-ycxi]

I have "center drilled" houses to run home runs to the panel before. Starting with a 3/4" hole at the far end of the house and increasing it to 1 1/4' and 2' as I got closer to the panel. The inspector was quite impressed with my work and complemented me on how neat and clean my work was.

[ubersham]

I think some of the limitations are because we used to run 14/2-3 (or even smaller) through walls, while today it’s more common to see 12/2-3 run through walls for additional safety and capacity when needed. The margin of safety between 14 and 12 awg wires is significant, and running 12 awg limits the heat, capacitive resistance, inductive resistance, and expansion those wires might otherwise experience with smaller wires. Running 12 awg is like future-proofing the home. I always recommend running 12 awg, as well as running CAT-6 to every room in the house (and 2-4 runs to every possible media location). CAT-6 is useful in so many ways that it just makes sense to run it before the drywall goes up.

[douglasboyle]

I had an inspector tell me the limit on the amount of romex in the hole was "There wasn't enough room for thermal expansion". I had to stifle a laugh. In his mind I think he expects copper to expand by orders of magnitude when it gets hot.

[JCWren]

I would argue that wall insulation has more effect on the temperature of the conductors than bundling does. Wires in open cavity walls can dissipate heat far easier than having a bat of fiberglass insulation or spray-in insulation around them.

[markhansen]

Carpenters sometimes call electricians and plumbers termites.

[CarlVanWormerAEGD]

Capacitance is not an issue for 60Hz wires. As stated by another commenter, the capacitance between the hot and ground conductors in a Romex cable is greater than the capacitive coupling between arbitrary pairs of Romex cable. The reason for limiting conductors in shared holes in the rules must be some of the other things you mentioned besides the capacitance.
If we assume that Romex has about 20pF per foot, 100' gives about 2000pF, which has a capacitive impedance of about 1 Meg Ohms at 60Hz. That would give about 100 micro-Amps of current flow. If we consider another Romex cable as close as it could be for that same 100' length, the capacitance would probably be ten times less. The result would be insignificant.

[Chris_In_Texas]

2:42 I have seen an electrician get killed from that issue, it was actually inductive coupling. The new wire run wasn't grounded running next to a live 7.2KV 3 phase run, which induced enough voltage and current into the new "dead" cable. He grabbed the cable to work on it, not verifying that there was a ground in place, and was electrocuted. That was preventable for sure. 😢

[lanceleavitt]

Like he said, it depends on your local inspector. With 4 conductors in a 1" hole, my inspector
said I could only have 2. --- Drilled a new 3/4" hole and re-ran the conductors. All about getting signed off. ---

[calvissuperman]

While we're on the subject of romex running, can you make a video on techniques to rolling out home runs? I've done it now twice, and it just seems like I'm missing some very simple tricks because it takes me FOREVER. Also, what staples do you use and how do you install them? The ones I've tried are a nuisance to put in, and I always end up smashing my thumb multiple times. Would love a video on BASIC techniques of pulling romex, drilling holes; hammering staples and boxes. Just can't seem to find a groove you know

[mkill]

Hey Swedish electrician here, damn you guys have a easy job. Here in Sweden you have to draw all wires in plastic pipes (when the installation are in walls). But that can also be very useful when you need to change wires/cabels.

[ottoroth]

I have a common practice of drilling a 3/4 hole, and if another run is needed, drill another hole. You can fit comfortably 3 runs of 12/2 and 14/3, and 4 runs of 14/2. My biggest concern of overcrowding is not the breathing factor, but drywall screws skewering the run! Though nail plates are used for some reason, a lot of people think longer screws are better to hang drywall, or put up my own home, I replaced a junky GE Slimline panel with a nice Square D. The original panel had no main cutoff, though it was installed in 1981, and passed inspe tion (?), and when I purposely forced tripped a Slimline breaker the damn breaker did not trip...so I could have just replaced all the breakers, but with that expense, decided a new panel was needed. Anyway, there was a siding nail stuck inside the service conductor leading to the panel from the meter. I replaced that wire bundle, opened the cover and saw the neutral was indeed poked. Yes, could have energized my whole house exterior....anyway, catch your " act" on the next video!

[csimet]

Agree... I too stick to two cables per 3/4" hole. Occasionally, I have to run three through and just up the hole size to 1". Just makes pulling the cable easier.

[ScrewThisGlueThat]

Dang Dustin, you nailed it again. Man I love this show and your truly a mentor of mine. I have been a general contractor for 30+ years and I still find a ton of value in your teachings.

[jimmeade]

Your "heat not an issue" argument works fine in typical inside walls, but it's worth considering in outside walls that are insulated. Many years ago, when I was in college, I worked at the local electric utility, and one of the things they asked me to do was to test various types of insulation and their effects on wires. We built a 4-segment wall, ran several conductors through it (14-2 WG Romex, 12-2 Romex, 12 AWG in conduit, 14 AWG in conduit, 14 AWG post and knob) through it, insulated the various sections with different insulating materials (none, fiberglass, cellulose, foam), installed thermocouples to measure the temperatures, and then ran each circuit at various increasing current levels. When we got to 20 amps on the 14-2 Romex circuit (yes, that exceeds NEC but can be a common mistake if 14-2 is connected to a 20A circuit breaker; the utility was aware that some service/panel upgrades used 20A breakers connected to 12 AWG wire at the panel that then connected to existing 14 AWG wire elsewhere in the house), the wall started smoking and caught fire after just 5 minutes of continuous load. The fire started in the foam section, then spread to the cellulose. Needless to say, the test was quickly terminated. The test results were shared with several organizations, and led to some of the electrical and building and insulation code changes we see today.

[kenbrown]

an independent lab ran testing on how many wires can be jammed in a hole without overheating them, so they put various numbers of cables in a hole, foamed the hole, like insulators now always do, and their determination was that you pretty much couldn't exceed 3 cables before you started overheating wires. and capacitance between wires? not a thing I've ever heard of. induced voltage, yes. never capacitance.
and if capacitance is the issue in the wire bundling charts, why is ambient temperature a factor?

[MEXATRON]

Currently waiting for my coworkers, thanks for being awesome with these videos ! Very nice way to kill time and obtain knowledge 🤟

[chrisluna]

I wish this channel was around when I was a first year. I've learned so much in just a few of your videos. Thank you, Sir.

[chrisneill]

310.15(B)(3)(a) provides a clear definition of multiple cables in a “bundle”. As a general rule, I stick to 3 which derates the conductors by 80%. This allows for other adjustments that might be applied in addition to bundling such as ambient temperature. Thanks for the video.

[tomreiter]

Good video. Something worth mentioning is the derating requirement in 334.80 should the holes be filled with caulk, foam, etc..

[tomcook]

Couple years ago, I ran a wood screw into a stud for a shelf bracket…pop went breaker

Opened the wall to find the screw went directly thru the hole, thru the Romex….

No slack to fix it with a wire nut, so I used a crimp butt connector, after crimping I soldered the connector to be safe and covered with heat shrink.