NM cable/deration

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nizak

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I did a residential rough in and had my home runs running down an exterior wall(will be insulated with cellulose insulation). I secured the NM cables using the plastic NM cable stackers that hold a total of 8 flat cables in 4 seperate slots. I am being told that this is a violation of 334.80.The way the stackers are constructed is that there is a thin strip of plastic between each slot that the wires fit into. I don't see anywhere where it says how much space has to be maintained, any thoughts on if this would be a code violation. thanks.
 

Hv&Lv

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I did a residential rough in and had my home runs running down an exterior wall(will be insulated with cellulose insulation). I secured the NM cables using the plastic NM cable stackers that hold a total of 8 flat cables in 4 seperate slots. I am being told that this is a violation of 334.80.The way the stackers are constructed is that there is a thin strip of plastic between each slot that the wires fit into. I don't see anywhere where it says how much space has to be maintained, any thoughts on if this would be a code violation. thanks.

310.15(1)or(2)? (trying this from memory...)
 

Ponchik

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310.15(1)or(2)? (trying this from memory...)

310.15(b)(2)(a)
specifies 24" if you have conductors or cables that are bundled together. But it doesn't specify the spacing between the cables if they are separated.

I think the installation that OP posted is OK and should pass inspection.
 

Hv&Lv

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310.15(b)(2)(a)
specifies 24" if you have conductors or cables that are bundled together. But it doesn't specify the spacing between the cables if they are separated.

I think the installation that OP posted is OK and should pass inspection.

I was refering to the cables touching somewhere within the 24" length. I looked up 310.15(B)(2)(a), and in the 2008 NEC they added "installed without maintaining spacing for a continuous length".
IMO, I agree with you, as long as the cables maintain some space throughout, no matter how small, ,he should pass. \
 

infinity

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If the without maintaining spacing installation has cable with a length that does not exceed 24" then you should be OK. Basically it's a judgment call on the part of the inspector. IMO stackers provide the requisite spacing.

(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 installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) 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.
 

Hv&Lv

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*Multiplication Factor of 1.08 from Table 310-16, 60?C column, 1990 NEC
**If 5 to 8 # 14-2 w/g NM cables are installed in a SI-1 cable stacker, ampacity derating should be considered.

http://multimedia.3m.com/mws/mediaw..._UoYTSev7qe17zHvTSevTSeSSSSSS--&fn=SIFSDS.PDF

I wonder how long they held those amperages on the wires? It would make a huge difference if it was 5 minutes, 60 minutes, or 3 hours IMO. I understand that derating should be considered, and to be honest, it will be hard to keep(maintain) spacing, any spacing, throughout any particular 24" section.
Personally, I can't see it being done, as the inspector could check the entire length and fail the installation if he finds the wires touching twice anywhere within any 24" section. Is it the best way? Probably not. However, IF he can maintain spacing, then by code, he should pass.
 

infinity

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Personally, I can't see it being done, as the inspector could check the entire length and fail the installation if he finds the wires touching twice anywhere within any 24" section. Is it the best way? Probably not. However, IF he can maintain spacing, then by code, he should pass.

IMO that is not what the requirement says, it says "installed without maintaining spacing for a continuous length longer than 600 mm (24 in.)". The conductors would need to touch for more than 24" continuous inches for derating to apply.
 

Dennis Alwon

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If you look on the bag they come in, it tells you to mind derating. The inspector is correct.
I don't see how it can possibly be considered derating since the cables are not touching the entire length. The fact that the bag states to mind derating does not necessarily mean you must derate. IMO, that is a CYA statement.
 

infinity

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I don't see how it can possibly be considered derating since the cables are not touching the entire length. The fact that the bag states to mind derating does not necessarily mean you must derate. IMO, that is a CYA statement.

I agree, saying "ampacity derating should be considered" is not an automatic requirement.
 

Hv&Lv

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IMO that is not what the requirement says, it says "installed without maintaining spacing for a continuous length longer than 600 mm (24 in.)". The conductors would need to touch for more than 24" continuous inches for derating to apply.

I see your point, however, I am reading this differently. I read this as the space has to be maintained for at least 24". Stud spacing is 16 inches, and the holes are considered supports. Can 8 wires be ran through the holes together? I have heard so many different numbers, some say 4, some say 8, I have heard 12...:?
 

iwire

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I agree that the manufactures recommendation does not have to be followed.

That said, I think it s clear we are going to have to change our thinking. The NFPA seems determined that we start considering derating much more often than we have in the past. In the last few code cycles they seem to be addressing this.

For example, the rule about a number of NMs through a fire stopped hole, or NM being used at 60C and SE being 60 in contact with insulation etc.
 

Dennis Alwon

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When entering a panel, IMO, it is best to add a horizontal block against the back side of the wall and staple the wires in pairs. This spreads the wires out and gives plenty of space. I also try and design my runs so they come in both top and bottom of the panel.
 

George Stolz

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I think it would be foolhardy to ignore the "advice" given on the bag, since it's so easy to comply with. I use zip ties instead, but the same concept applies; when you reach nine CCC's, simply start using the other side of the stud bay.
 

infinity

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I see your point, however, I am reading this differently. I read this as the space has to be maintained for at least 24". Stud spacing is 16 inches, and the holes are considered supports. Can 8 wires be ran through the holes together? I have heard so many different numbers, some say 4, some say 8, I have heard 12...:?

8 or 80, if the hole is not fire stopped or filled with a draft stopping material. The issue is, as you've mentioned, is there adequate spacing between the cables in the area between the stud holes.

Regarding the 24", I can take 20 NM cables and tie them together in a tight bundle with cable ties and derating will not apply as long as there is spacing between the cables on either side of the bundle.
 

Hv&Lv

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8 or 80, if the hole is not fire stopped or filled with a draft stopping material. The issue is, as you've mentioned, is there adequate spacing between the cables in the area between the stud holes.

Regarding the 24", I can take 20 NM cables and tie them together in a tight bundle with cable ties and derating will not apply as long as there is spacing between the cables on either side of the bundle.

I realize this is getting extreme, but in your example, you can take 20 NM cables, tie them together tightly, and it is ok as long as there is space on either side, and the cables do not touch continuously for 24". So can I tie these same 20 cables together every 8 inches for however long I need as long as there is some space between each cable on each side of the ties?
 

infinity

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I realize this is getting extreme, but in your example, you can take 20 NM cables, tie them together tightly, and it is ok as long as there is space on either side, and the cables do not touch continuously for 24". So can I tie these same 20 cables together every 8 inches for however long I need as long as there is some space between each cable on each side of the ties?

You can make a continuous bundle up to 24" long. For longer than 24" 310.15(A)(2)Exception might come into play.
 
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