maximum number of cables in single hole?

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  #1  
Old 06-14-06, 10:45 PM
ddr
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maximum number of cables in single hole?

Hey folks,

I canít seem to find anything in the NEC about how many cables may be pulled through a single bored hole in a framing member (I know the edge of the hole must not be closer than 1.25Ē from any edge without a steel plate). Does such a regulation exist for residential wiring? If so, does it go by the number of cables or the total of the conductors?

Also, is there a rule limiting the number of cables which may be run vertically through a single 14.5Ē stud bay? (Again cables or conductor total?)

Any problem with interference from induction/EM fields? (I know, I know; Iím getting paranoid with that one.)

Thanks in advance...
 
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  #2  
Old 06-15-06, 03:46 AM
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It goes by the total number of current carrying conductors when determining if you need to de-rate when running wires through bored holes.

With regard to the vertical runs, no there is not a limit, but keep the cable tv and telephone wires out of this cavity. You could have emf problems there. You will also have to install dead wood or some other kind of brace to get the required support on your wires. Stackits are cool.
 
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Old 06-15-06, 08:01 PM
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Any problem with interference from induction/EM fields? (I know, I know; Iím getting paranoid with that one.)
[/QUOTE]

When it comes to worrying about E/M it depends on the current drawn through the wires. I have seen large current wires push themselves apart over time but which way they go depends on which way current is going. As for worring about frequency intereference devices that are operated on multiples of 60Hz or what ever country your in could be affected depending on their design.
 
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Old 06-16-06, 05:41 AM
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I thought derating only applied to conductors in conduit or some kind of enclosed wireway. As far as I know the only limitation on wires through a framing member is the size of the hole.
 
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Old 06-16-06, 10:18 AM
ddr
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Thanks for everyoneís input.

Iíve been going through the NEC and checking on other forums (like Mike Holtís) and even there the inspectors/electricians canít seem to agree on it. The question seems to stem from bundling: if the wires are separated along the run but then brought into close proximity in a hole, is that momentary closeness the equivalent of bundling and therefore subject to derating? Some say yes, others say no, still others say yes but only if the hole they are passing through is over 24Ē which makes the hole a conduit or raceway.

The holes Iím talking about would be 1.5Ē long through a sole plate from basement into first floor wall and then through a double top plate (3Ē) from first floor wall into a crawl space.

They also say it only applies when having more than 4 current carrying conductors next to each other (generally 2 12/2 cables). Then one guy says that 12/3 cables should be allowed since thereís no current on the neutral. To my understanding this is only if the loads on the two hots are identical, otherwise (assuming a properly wired multi wire circuit) the neutral will be carrying the difference of the two loads ó am I losing it or is this guy just plain wrong?

Add to this the fact that almost everything said is tied to whether or not a fire-stop sealant is used ; if yes then you canít do it, if no, then itís okay. (At this point Iíve broken out the Tylenol...)

Then they start to argue about the grouping, i.e. if you have three cables through a hole for a stud cavity run and you exit all three through another hole they are considered bundled if there is no physical separation in between, such as a cross member to which they are nailed with adequate space between each cable for cooling purposes; without this, the cables, even if not physically bound together, will tend to stay in a group making them ďbundledĒ and a possible fire hazard, especially if run through a stud cavity with insulation.

So whatís a DIYíer to do?
 
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Old 06-16-06, 11:50 AM
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If you are running them through the same hole in the bottom of the stud cavity, and then through the same hole in the top of the stud cavity, how are you going to keep them separated inside the stud cavity?

A properly spaced hole in a 2x4 does not allow much room for the hole, and limits the diameter it can be. Therefor you cannot pull many cables through it without risking damage to the cables.

Why even ask the question? Just make two holes at each end and avoid the question.
 
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Old 06-16-06, 05:07 PM
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If you are running them through the same hole in the bottom of the stud cavity, and then through the same hole in the top of the stud cavity, how are you going to keep them separated inside the stud cavity?
racraft,

The separation of the wires was something I was reading about on another site. According to this guy youíre supposed to install a furring strip or something across the stud bay to act as a brace and nail the cables an inch or so apart to maintain separation. Believe me others posted back to say he was nuts.

Why even ask the question? Just make two holes at each end and avoid the question.
I'm sorry if the question seemed silly. My house was built in 1952, had 60A service and 3, yes 3 fuses feeding the whole house (and one of them was dedicated to the furnace). There were only three cable holes drilled above the fuse box and the cables ran up to a crawl space; everything stemmed from there.

Since then the service has been upped to 100A and a breaker panel installed, but with running lines for A/Cís, computers, and splitting off some of the original circuits to smaller loads, there are 16 or 17 circuits in there now and Iíve got cable running everywhere in the basement. Also, NYC code requires (or required - need to check the current code) conduit to protect more than 18Ē of exposed cable in accessible areas. In short, my basement looks like a power substation and I was hoping to get some wires back in the walls without turning my sole/top plates into Swiss cheese, thus my question about putting more than one wire through a hole and my previuos question about 12/3 vs. 12/2/2.
 
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Old 06-16-06, 07:30 PM
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2005 NEC®© 310.15 (B) (2) Adjustment Factors.

(a) More Than Three Current-Carrying Conductors in a Raceway or Cable. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are stacked or bundled longer than 600 mm (24 in.) without maintaining spacing and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor. .

What this means, very simply, is that after applying the derating factors for #14 and #12 NM-B the allowable number of current carrying wires that can be bundled together is 9 without having to change wire and/or breaker sizes. This means you can run 4 #12 NM-B cables or 4 #14 NM-B cables, or 4 12-3 or 4 14-3 cables. The neutral DOES NOT count on a residential multiwire circuit, nor does more than one traveler on a 3 way circuit. A 14-4 or 12-4 ( or 14-2-2 or 12-2-2) cable used for running a light-fan-heater unit where all share a common neutral has only the neutral and one hot wire counted. A 14-2-2 or 12-2-2 must be counted as 4 if 2 separate circuits are run in it (2 neutrals, 2 hots)

It doesn't matter if you tie the cables together with cable ties or not, most AHJs will consider cables run through the same hole on both ends of a stud cavity bundled UNLESS a stacker of some kind that separates the cables is used.

That said, 4 is probably the most number of cables you would want to be pulling through the same hole, and if they're #12s you would probably be needing a hole large enough to require notch plates.
 

Last edited by itsunclebill; 06-16-06 at 11:04 PM.
  #9  
Old 06-16-06, 11:11 PM
ddr
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Thanks for the info itsunclebill.
 
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Old 06-17-06, 05:15 PM
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Originally Posted by racraft
Why even ask the question? Just make two holes at each end and avoid the question.
I wondered the same thing. Got me thinking of the 'see how many people you can stuff into a telephone booth contest'.
 
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