any limit to # wires in same stud hole?

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Old 08-12-09, 02:49 PM
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any limit to # wires in same stud hole?

I will be running wires for multiple circuits in the same wall. I don't want to have to drill a bunch of holes. I thought I would drill a large single hole -- maybe 1-1/2" diameter. The wall is not load-bearing -- it only supports itself/drywall.

Does the code limit how many wires you can run in the same hole (assuming you protect them properly with metal plates)?

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Old 08-12-09, 03:02 PM
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Four standard 14/2 or 12/2 is the upper limit before derating affects the circuit -- if the cables are larger sizes, then more detailed calculations would need to be done. However standard practice is to put two cables each through 7/8" holes drilled a few inches apart vertically. This method does not require metal plates. Not to mention that a 7/8" auger bit can drill a couple dozen holes in the time it would take to hole saw a single 1-1/2".
 
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Old 08-12-09, 06:48 PM
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Thanks for your quick reply -- I have never used an auger bit - will try it. Can a 7/8" hole take two 14/3 wires?
 
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Old 08-12-09, 07:17 PM
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Sure the 7/8 inch auger bit hole will take 2 X 14/3 without any issue

For myself I keep couple of diffrent size auger bits on hand the 9/16 and 7/8 is most common used in resdentail usage however I do have couple larger one for larger cable or conduits if need to.

Merci,Marc
 
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Old 08-13-09, 05:58 AM
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The two air conditioners are 8,000 btu - 6.8 amps and 115v. I know that each will need its own circuit breaker, but would they require 14/3 or is 14/2 okay?

All the manufacturer would say is that it is a "3-prong standard plug". I thought standard plugs only require 2 conductors plus the ground.

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Old 08-13-09, 06:39 AM
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You can use 14/2, which is 2 conductors plus ground. No reason for 14/3.
 
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Old 08-13-09, 08:43 AM
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Originally Posted by rambelmont View Post
The two air conditioners are 8,000 btu - 6.8 amps and 115v. I know that each will need its own circuit breaker, but would they require 14/3 or is 14/2 okay?
If they're near each other I'd probably put them both on one 20A circuit with #12/2 cable, however you could do two #14/2 cables also.

All the manufacturer would say is that it is a "3-prong standard plug". I thought standard plugs only require 2 conductors plus the ground.
I think they mean three prongs as in hot, neutral, ground (NEMA 5-15P).

I have never used an auger bit - will try it. Can a 7/8" hole take two 14/3 wires?
It's a little rough to handle and throws chips everywhere, but rips through framing lumber in a hurry. Recommended only if you have a 1/2" chuck drill motor. Corded is best, but some of the more substantial cordless drills can handle an auger. Yes, two #14/3 can go through a 7/8" hole. Basically anything that fits loosely is okay - if you have to really yank on it to get it through, the hole is too small.
 
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Old 08-13-09, 09:37 AM
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Thank you both for responding -- I bought a set of auger bits from HD last night -- and yes, I will be using a corded drill.

The air conditioners will be in separate bedrooms, and the panel has lots of room, so I guess separate 15 amp circuits would be best.

Thanks again for your fast answers.
 
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Old 08-19-09, 03:07 PM
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"Four standard 14/2 or 12/2 is the upper limit before derating affects the circuit"

That would be 8 conductors. I thought you could have 10 conductors without derating and if you had more than 10, you only had to derate if they traveled together for more than 2 feet? I thought I saw this somewhere. Anyway, if you have 14/3 wire, since only one traveler is hot at a time, does that only count as 2 conductors just like 14/2? I ended up with 4 14/3 cables in a 4 stack cable last night and wasn't sure if that was OK?
 
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Old 08-19-09, 04:25 PM
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Strictly speaking the need to derate enters the picture once you exceed three current-carrying conductors. The practicality of not having to derate until you exceed nine current-carrying conductors is because of the limits placed on #14 through #10 conductors with type THHN insulation. You are correct though that derating does not come into play IF the conduit containing the individual conductors is not more than 24 inches in length.

As for the 3-way switch example, that is why the code is worded as "current-carrying" conductors so no, you would NOT count both travelers in a three-way circuit.
 
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Old 08-19-09, 06:11 PM
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so it is when you exceed 9-not when you exceed 10?

I have a stacker that has 3 14/2 cables and 1 14/3 cable to fan/light so that is 9 current carry conductors. I have another 14/3 cable for 3 way switch arrangement (2 more conductors) that needs to follow same path down stud to box. so do I have to run it down the stud on the other side of box and enter box from other side avoid exceeding 9 conductors? or is a cable stacker not considered the same as conduit since it really is not tightly restricting the cables? the wall is 2x6 and I drilled 1" hole in top plate(maybe 1 1/4"?) there is still plenty of room but does the other cable have to come through different hole in top plate?
 
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Old 08-19-09, 06:50 PM
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I am not a code-enforcement officer nor have I ever submitted anything to the code review panels for consideration. My degree isn't even in electrical engineering although I have needed to follow NEC guidelines when I did design work in my previous life.

The questions you ask would be covered in Chapter 3 of the NEC. This chapter in the 2002 code (the one I have available at the moment) runs some 106 pages. There is no way that I (or anyone else) could break that down to just a few sentences. Even limiting ourselves to Article 310 would take far more room than is available on this forum but here is what is said in Table 310.15(B)(2)(a) Adjustment factors for more than three current-carrying conductors in a raceway or cable For 4-6 Current-Carrying conductors you may only use 80% of the ampacity listed in Tables 310.16 through 310.19 as adjusted for ambient temperature if required. For 7-9 the factor is 70%. For 10-20 the factor is 50% and it goes on.

BUT, remember that this is for conductors in a raceway or cable. You are using several cables, each of which contain no more than three current-carrying conductors. Therefore, there is no clear answer to your question. Using the "stackers" keeps the individual cables separate and that allows for the free air to cool the individual cables. In my opinion (which if accompanied with a dollar bill will get you a cheap cup of coffee) as long as you use the stackers and DO NOT "bundle" the individual cables (don't use ty-wraps for a neat job) you can ignore the derating requirements in this particular situation. Likewise, since running the cables through the hole in the framing member will be less than the 24 inch maximum for not derating you do not have to derate for running all the cables through the same hole.
 
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Old 08-19-09, 08:59 PM
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3M, the manufacturer of the stackers, has made the claim and published experimental data to demonstrate that their product does not contribute to excessive wire heating when used as labeled. The temperature increases were still well within safe limits for NM cable even with eight 14AWG cables (16 CCC) in the stacker all loaded up to maximum ampacity of 15A.

However, the code still has not taken an official position on derating and stackers despite the data to suggest that they can be used safely well above the conventional derating limits. Until the code makes an article regarding their use, it is largely up to the inspector to decide how to regulate stackers.

In my opinion your installation sounds perfectly fine. Except in rare circumstances, 14/3 cable counts as only two CCC.
 
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