Replies

1. 
   BillHartmann | Jun 15, 2009 06:15pm | #1

   First of all their is NO PROBATION ABOUT USING NM IN CONDUIT, PERIOD.

   Also NM is used all the time where there is limited or no air flow.

   There is no problem with using NM with DPC.

   .
   William the Geezer, the sequel to Billy the Kid - Shoe
2. 
   gfretwell | Jun 15, 2009 06:20pm | #2

   RX can be used in conduit or in insulation. The only derating issues are when you have too many conductors bundled together.
   In pipe the issue is usually "fill" since an oval cable gets measured by it's widest dimension. You fill a conduit up pretty fast.
   In insulation, any contact is considered bundled, even if it is a single 2x4 that is penetrated and insulated (the foam up the hole thing). That is a new code change. We won't be having that big hole in the top plate above the panel with 15 RX cables foamed in there anymore.

1. 
   peedee | Jun 16, 2009 06:10am | #3

   To Bill - I'm glad we agree on that, if only I could convince the local BIs... do you happen to recall which provision of the code I can refer them to should this issue arise again?gfr- I've not seen NM referred to as RX before but my knowledge is admittedly limited - please enlighten me further. Also I'd like to stay up on current code and you mention "That is a new code change", which code are you referring (e.g. IRC, UBC, and year?)Thanks,
   David

1. 
   BillHartmann | Jun 16, 2009 07:19am | #4

   The only thing that I know of is the section that specifies NM and give the place that it can and can't be used.Insulation is not mentioned at all..
   William the Geezer, the sequel to Billy the Kid - Shoe

2. 
   rasconc | Jun 16, 2009 08:18am | #6

   He is just abreviating Romex. For those who have fought for it Freedom has a flavor the protected will never know.

3. 
   gfretwell | Jun 16, 2009 08:56am | #7

   The code change is to 2005 National Electrical Code article 334.80 and says when 2 or more cables are bundled and go through framing that is insulated, firestopped or sealed with foam you must apply derating per 310.15(B)2(a).
   2008 added "caulk"

   Edited 6/16/2009 1:57 am ET by gfretwell

1. 
   peedee | Jun 16, 2009 03:55pm | #8

   Thank you for the clarification, gfr, this is why I think of BT as BrainTrust, as well as BreakTime.Regards,
   David

2. 
   BillHartmann | Jun 16, 2009 07:20pm | #9

   I don't have 2008. But here is the 2005."334.80 AmpacityThe 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.Where more than two NM cables containing two or more current-carrying conductors are bundled together and pass through wood framing that is to be fire- or draft-stopped using thermal insulation or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a)."And this is from the Handbook. Often it gives some clarification or background that helps make more sense, but not in this case."Section 310.15(B)(2)(a) states in part: ``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).'' Failure to comply with the appropriate
   adjustment ampacity derating called for by this table, where nonmetallic-sheathed cables may be stacked or bundled, can lead to overheating of conductors. For the 2005 Code, a new derating requirement was added to prevent overheating of Type NM conductors where passing though draft- and fire-stopping material."It would be interesting to see the original reasonings and discussions. It sounds like something that might have gotten extended more than makes sense.I can't see where cables going through 1 1/2" top plate (allowed with stacked framing)or even 3" is that much different with a squirt of foam or caulking. BTW, it reads MORE THAN TWO CABLES, not "says when 2 or more cables "And I see this;"320.80 Ampacity
   The ampacity shall be determined by 310.15.(A) Thermal Insulation Armored cable installed in thermal insulation shall have conductors rated at 90°C (194°F). The ampacity of cable installed in these applications shall be that of 60°C (140°F) conductors. 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."And the Handbook."The requirements for armored cable installed in thermal insulation recognize the decrease in heat dissipation capability of cables. New for the 2005 Code, the last sentence brings this section into harmony with 334.80 for Type NM cable and clarifies that the 90°C degree insulation may be used for derating purposes. Cable marked ``ACTH'' indicates an armored cable rated 75°C and employing conductors having thermoplastic insulation. Cable marked ``ACTHH'' indicates an armored cable rated 90°C and employing conductors having thermoplastic insulation. Cable marked ``ACHH'' indicates armored cable rated 90°C and employing conductors having thermosetting insulation."But while the section on AC does mention thermo-insulation, but the section NM does NOT say anything about thermo-insulation except where it is part of fire blocking.Again does not make any sense.
   .
   William the Geezer, the sequel to Billy the Kid - Shoe

1. 
   gfretwell | Jun 25, 2009 04:01am | #10

   http://gfretwell.com/electrical/NEMA%20Romex%20in%20foam%20study.pdf

2. 
   mmoogie | Jun 25, 2009 05:10am | #11

   Have you (or you too, Bill) ever had an inspector flag you for typical residential wiring where there are 2 or 3 wires passing through holes in studs or plates w/foam around them and/or dense-pack cellulose or foam insulation in the walls, and loads that were not derated?Steve

   Edited 6/24/2009 10:11 pm by mmoogie

3. 
   gfretwell | Jun 25, 2009 08:36am | #12

   You would really need five #12 or #14 /2 cables before derating would make you upsize the wire. You derate from the 90c column and have to size the wire from 240.4(D).

2. 
   rasconc | Jun 16, 2009 08:16am | #5

   These people are way out of control!  Are you talking about regular foam or fire caulk?  I can see if it is the 15 you are talking about but a couple poking through a plate should not be a problem.For those who have fought for it Freedom has a flavor the protected will never know.