Securing Type NM Cable

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dduffee260

dduffee260

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Texas
I am not a code expert but I believe it says to secure type NM cable within 8" or 12" from the box then every 3' 6" up the walls. This is how we have always stapled it. My question is this. Can we install one staple in the wood then tywrap the bundle of wires on that staple? This seems like it would help when you have 5 or 6 wires going up the wall. I also seen where Caddy makes a cable clamp device where you can put several wires in the clamps. Thanks for the input.
 
Re: Securing Type NM Cable

Can we install one staple in the wood then tywrap the bundle of wires on that staple? This seems like it would help when you have 5 or 6 wires going up the wall.

Technically that would be bundling and you would have to derate. Also, depending on the size of the framing you may not be able to maintain the 1 1/4 rule.

Proper way, and this applies to other wiring methods besides NM, is to use stackers as you suggest, Caddy "Colorado Jims" or any other method that puts them away from the stud.

At times when I've had a lot of cables in one bay I put 1x2's inside the bay every couple of feet and stapled the cables to them.


-Hal
 
Re: Securing Type NM Cable

First of all it is 4'-6" between staples.

We have been using the zip tie method. The AHJ in our area is allowing this to be used how you explained.

NM cable is already basically derated. Unless you go over nine current carrying conductors.
 
Re: Securing Type NM Cable

We use the furring stackers for all applications and when there are a bunch of runs into a 5 or 6 gang we back to back the stackers and tiewrap any that don`t fit in slots.You still have to secure within required distance from a box but as long as after that you keep the stackers over 24 ins apart bundling is not an issue.
 
Re: Securing Type NM Cable

Where are you learning the codes about derating?

NM cable is NOT derated, see Article 310.15(B)(2)(a), where more than three current carrying conductors in a raceway or CABLE exceeds 3, or where multi conductor cables are stacked or bundled longer than 24", use Table 310.15(B)(2) (a).

At best, with 9 current carrying conductors, Or approx. 4-12/2 Nm cables) if they will never get over 86 deg. F, that is 25 amps for #12AWG, at 60 deg C. you now have only 17.5 amp capacity.

25 X .70 = 17.5 Amps

Now figure -- what? 130 deg. F, once they enter the attic? That is another .41.

17.5 amps X .41 = 7.17 Amps

That leaves you with #12 Cables, rated at 7.17 amps, gotta breaker that small?

OR - If ya prefere, you can do the long mathmatics,(310.15(C). It's just easier, and faster to follow the codebook charts, and THEY have done all the difficult math.
 
Re: Securing Type NM Cable

the wire itself is rated at 90 degrees for the purpose of derating, not 60 degrees
 
Re: Securing Type NM Cable

electric_instructor,

334.80 allows us to use the 90?C column to begin our derating.

for nine #12 conductors:

30 amps x 70% = 21 amps.

In your attic

21 amps x .76 = 15.96 amps.

True, 9 bundled current carrying conductors in an attic are not allowed on a 20 amp breaker, but we don't need to go looking for a 7.17 amp breaker either.

The original post wasn't about attics, but about securing NM in walls. for that purpose, sparkslord was basically correct when he said NM is basically derated for up to nine current carrying conductors
 
Re: Securing Type NM Cable

Originally posted by electric_instructor:
Where are you learning the codes about derating?
Click to expand...
Your new so I will tell you that is not a way to gain respect around here. :p

334.80 Ampacity.
The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60?C (140?F) conductor temperature rating. The 90?C (194?F) rating shall be permitted to be used for ampacity derating purposes, provided the final derated ampacity does not exceed that for a 60?C (140?F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.11.
Click to expand...
Many of the members here are as sharp on the NEC and electrical theory as you will ever find in one place.

Originally posted by electric_instructor:
NM cable is NOT derated,
Click to expand...
In sizes 14, 12 and 10 it is already derated in a way, although we do not call it that.

Because of 240.4(D) in general we do not have to downsize the OCP on 14, 12 and 10 AWG NM until more than 9 current carrying conductors are bundled.

I agree entirely with eprice's example. :cool:

[ October 25, 2005, 12:03 PM: Message edited by: iwire ]
 
Re: Securing Type NM Cable

You have shown me the error of my ways. You are correct! :D

15.96 amps is much better. I operate under the experience that the cables will most likely enter an attic, but that isn't always so!

If that were the case and all of the #12 cables were being used for 15 amp circuits - COOL!

Thanks for the reminder, I do need one from time to time. ;)
 
Re: Securing Type NM Cable

I've been using the zip tie method for a little over a year now, and the inspectors have never batted an eyelash. It's much cheaper than 3M's Stackers, and faster than adding furring strips. As long as the zip tie is not tight-tight, and not any closer together than 2', it shouldn't be called bundling. Really, all you need to do is hold the cables centered on the stud, and not lashed down for hurricane force winds. As one of my collegue's put it, using a zip tie stapled to the stud to secure a number of cables is not much different than that same number of cables passing through a single bored hole at that same interval.

[ October 25, 2005, 10:39 PM: Message edited by: mdshunk ]
 
Re: Securing Type NM Cable

To see the ultimate in NM installations, click here.

Obviously a case where craftmanship was valued more than the money spent for the labor.

Roger
 
Re: Securing Type NM Cable

Originally posted by electric_instructor:

15.96 amps is much better. I operate under the experience that the cables will most likely enter an attic, but that isn't always so!

If that were the case and all of the #12 cables were being used for 15 amp circuits - COOL!
Click to expand...
Once they do enter the attic, there is probably not a need to keep them bundled, so you would not apply both the 70% derating for bundling and the .76 factor for temperature. In the attic the ampacity of the #12 conductors would be

30 amps x .76 = 22.8 amps.

the lowest ampacity in the run would still be the 21 amps in the walls.
 
Re: Securing Type NM Cable

The CODE does cover the "bundleing of cabeles through drilled holes. aside from the 1-1/4" required spaceing (300.4(A)(1), 334.80 does mention it.

I would love to understand where the CODE says that you can derate conductors at differant rates, based upon differant parts of that conductor?

Not trying to be a smart-A**, just don't recall seeing that part! LOL
 
Re: Securing Type NM Cable

its the sheathing of the conduit that is rated 60 degrees, not the covering of the wire.
 
Re: Securing Type NM Cable

Can ya derate for Number of conductors here -- then forget that, and derate again, somewhere else for temperature?

That wouuld be wonderful, if so! Specially in a refinery, making long runs, where ya have many conductors at first, then high temps later, near the crackers!

Lemme know how! I'd LOVE it! :D
 
Re: Securing Type NM Cable

OH, and back to the origional question!

It's 8" without a clamping means, and 12" if ya gotta clamp. And of course 4 1/2' after that, as already stated. :)
 
Re: Securing Type NM Cable

Originally posted by electric_instructor:
Can ya derate for Number of conductors here -- then forget that, and derate again, somewhere else for temperature?

That wouuld be wonderful, if so! Specially in a refinery, making long runs, where ya have many conductors at first, then high temps later, near the crackers!

Lemme know how! I'd LOVE it! :D
Click to expand...
310.15(A)(2) implies that you can have more than one calculated ampacity within a given run. If you can't, what would be the reason for including the exception?

Conductors are derated because of factors that affect their ability to disipate heat. Are you saying that having conductors bundled in the walls will effect how they disipate heat in the attic?? How does the temperature in the attic affect the way the bundled conductors dispate heat in the wall?

Since the NEC is a permissive code, let me turn the question around and ask, where does the code require me to apply every factor that may affect the conductor somewhere along the run, to every portion of the run, even where that factor does not exist?
 
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