2008 334.80 spacing between cables

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Minuteman

Minuteman

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Where more than two NM cables containing two or more current carrying-conductors are installed in contact with thermal insulation without maintaining spacing between cables, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a).
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So how far is this spacing to be? I'm hearing one local AHJ uses the IRC and the IRC says 24". Seems like this could be difficult to comply with on the outside walls in most new kitchens. For that mater, some new homes what thermal insulation in ALL walls.

So how far apart should these be?
 
Minuteman said:
So how far is this spacing to be? I'm hearing one local AHJ uses the IRC and the IRC says 24". Seems like this could be difficult to comply with on the outside walls in most new kitchens. For that mater, some new homes what thermal insulation in ALL walls.

So how far apart should these be?
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That quote was from 2008 correct?
 
Just took my 6 hour CEU on the '08, and this was one of the things that caught my attention as a potential problem. I don't understand why the CMP did not just fix a value for the spacing. Leaving something up to the AHJ is like leaving it up to my wife, you'll not get the same answer twice. :rolleyes:
 
I'm not sure the study I linked to was the right one,... does anyone have access to this one , It might give insight to as to what distance is effective

NM Cable Bundles
Installed on or In Thermal Insulation, November 2005.​
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7-74 Log #3152 NEC-P07
Final Action: Accept


(334.80)

____________________________________________________________

Submitter: ​

Travis Lindsey, Travis Lindsey Consulting Services



Recommendation:
Add an additional third paragraph to 334.80 to read:


Where more than two NM cables containing two or more current-carrying
conductors are installed in contact with thermal insulation without maintaining
spacing between cables, the allowable ampacity of each conductor shall be
adjusted in accordance with Table 310.15(B)(2)(a).

Substantiation: ​

Recent field experimentation shows that NM cables which are


grouped or bundled together for varying lengths and installed in contact with
thermal insulation in walls and ceilings can exceed the maximum allowable
design temperatures of the insulation. Even when the circuit currents were
limited to eight percent or less, temperature exceeded 90?C (194?F).
Full details are contained in the test report entitled​

NM Cable Bundles


Installed on or In Thermal Insulation, November 2005.

Note: Supporting material is available for review at NFPA Headquarters.

Panel Meeting Action: Accept
Number Eligible to Vote: 14
Ballot Results: ​

Affirmative: 13 Negative: 1



Explanation of Negative:

ADAMS, M.: NECA believes this proposal is too restrictive. ?In contact with
thermal insulation? is not the same concept as in the present second paragraph,
which envisions completely surrounding bundled NM cables with thermal
insulation or sealing foam. Also, since ?bundled? is not a term defined in the
NEC, accepting this proposal could preclude use of standoff type cable clamps.
While intended to maintain space between adjacent NM cables, multiple cables
installed in standoff clamps still touch in places, and might also touch thermal
insulation. We do not believe that NM cables should be derated under this
installation circumstance.​
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Minuteman said:
...Leaving something up to the AHJ is like leaving it up to my wife, you'll not get the same answer twice. :rolleyes:
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Is that your phone ringing?:smile:
M. D. said:
I'm not sure the study I linked to was the right one,...
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The file at copper.org had a late 2002, early 2003 date.
 
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