ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
AreMetal Ladders Ever OK For Electrical Work?
by HotLine1. 01/22/18 07:31 PM
Photocell
by twh. 01/22/18 05:06 PM
VDE 0100 to introduce AFCIs
by sparky. 01/20/18 05:09 PM
MRI LED lights dimmer control replacement - wow!
by Potseal. 01/19/18 08:52 PM
New in the Gallery:
Housebilding DIY wiring
SE cable question
Who's Online Now
0 registered members (), 24 guests, and 12 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Page 1 of 2 1 2
Foam insulation cable derating #192300
02/06/10 03:25 AM
02/06/10 03:25 AM
C
Check Pilot  Offline OP
Member
Joined: Nov 2005
Posts: 141
Edmonton Alberta Canada

It's been a while since I've had to ask a question here, now that I have retired from the EC business. (and my other job as a Civil Aviton Inspector as well - it's nice to get older and retire).

However, once the neighbours know about your past, I get questions and asked for advice about electrical installations. One of them has me flummoxed since I had not run into this one before.

He is doing a new basement installation to add a new living space in the basement and the 2X6 walls are being wired for all kinds of stuff including CAT 5 and every other kind of who knows what its for, cable including the basic electrical outlets, switches and fairly elaborate lighting system in a suspended ceiling system.

However there are a few places where 4 NMD 90 cables could be run up the 2X6 studs from just above the concrete floor level to the ceiling and these are on outside walls that he would like to spray with foam insulation.

I have checked both the CEC and NEC codes ad nauseum, about spraying insulation into the interior of the wall stud cavities and can find about zero information about any requirement to derate the cables for that kind of insulation. We all know about the usual batt insulation stuff but it seems to me that maybe the same rules that might not apply since there is no air flow in spray insulation as in fiberglass or rockwool insulation.

Has anyone here have information, experience or a code requirement about spray foam insulation applied on outside walls that require derating of the conductors?

Last edited by electure; 02/06/10 10:24 AM. Reason: Double Posting
Work Gear for Electricians and the Trades
Re: Foam insulation cable derating [Re: Check Pilot] #192303
02/06/10 11:35 AM
02/06/10 11:35 AM
Tom  Offline
Member
Joined: Jan 2001
Posts: 1,044
Shinnston, WV USA
The NEC does not differentiate between fiberglass or spray in foam. If you look at 334.80 in the 2008 NEC, the last paragraph requires an ampacity adjustment.

If you do the ampacity adjustment, you'll start in the 90 degree column and adjust that with a 70% multiplier for 8 current carrying conductors. That works out to 21 amps for #12 and 17.5 amps for #14, both of which exceed the maximum circuit breaker size for both sizes.

I'd say that there is no problem running 4 two conductor cables.

Tom


Few things are harder to put up with than the annoyance of a good example.
Re: Foam insulation cable derating [Re: Tom] #192304
02/06/10 11:47 AM
02/06/10 11:47 AM
L
leland  Offline
Member
Joined: Aug 2007
Posts: 853
Lowell area, Ma. USA
[quote=Tom]The NEC does not differentiate between fiberglass or spray in foam. If you look at 334.80 in the 2008 NEC, the last paragraph requires an ampacity adjustment.

If you do the ampacity adjustment, you'll start in the 90 degree column and adjust that with a 70% multiplier for 8 current carrying conductors. That works out to 21 amps for #12 and 17.5 amps for #14, both of which exceed the maximum circuit breaker size for both sizes.---


My guess is it will soon. My only caution with the foam is,it gets hot as it cures,so any low volt use a good PVC/Poly insulation.I have had times where the cheap typical phone cable has sufferd damage.
I'd say that there is no problem running 4 two conductor cables.


Last edited by leland; 02/06/10 11:48 AM.
Re: Foam insulation cable derating [Re: leland] #192314
02/06/10 07:22 PM
02/06/10 07:22 PM
Obsaleet  Offline
Member
Joined: Apr 2003
Posts: 362
Pa
I would be more concerned if the the foam would react with the rx insulation.

Ob


Choose your customers, don't let them choose you.
Re: Foam insulation cable derating [Re: Obsaleet] #192317
02/06/10 08:07 PM
02/06/10 08:07 PM
T
Texas_Ranger  Offline
Member
Joined: Dec 2001
Posts: 2,409
Vienna, Austria
Yes, conduit seems like a good idea. Some kinds of foam insulation (particularly the stuff sold in small cans to the homeowner) are supposed to react with PVC and soften it. Better safe than sorry!

Re: Foam insulation cable derating [Re: Texas_Ranger] #192319
02/06/10 08:36 PM
02/06/10 08:36 PM
Trumpy  Offline

Member
Joined: Jul 2002
Posts: 8,231
SI,New Zealand
Over here in New Zealand we use a different grade of PVC cable for these sorts of installations.
It's called Non-Migratory PVC.
Here's a link to the manufacturers specification:

Clicking this link will open a PDF file

Re: Foam insulation cable derating [Re: Trumpy] #192322
02/06/10 10:15 PM
02/06/10 10:15 PM
T
Tesla  Offline
Member
Joined: Jun 2004
Posts: 1,273
Sacramento, CA
Derating of Romex cable starts at the rating of the cable: 60 degrees Centigrade.

This reduced rating vs the underlying THWN-2/ or THHN reflects the fact that the cable sheath insulates...

The rise in super-insulated homes may well cause the Code Committee to revisit this issue. But as it stands, no NEC provision exists to derate based upon spray in foam. For my money it should be treated as if were running underground.


Tesla
Re: Foam insulation cable derating [Re: Tesla] #192323
02/07/10 12:19 AM
02/07/10 12:19 AM
L
leland  Offline
Member
Joined: Aug 2007
Posts: 853
Lowell area, Ma. USA
1981- 2010- derated once.

Never ever to this day had a problem. In any application.

Re: Foam insulation cable derating [Re: leland] #192331
02/08/10 12:26 PM
02/08/10 12:26 PM
M
mbhydro  Offline
Member
Joined: Feb 2003
Posts: 349
Winnipeg MB Canada
If you watch any of the Mike Holmes renovations shows from Canada if he has an open outside wall open on the inside, he foams it.

I am sure I have seen him order foam for existing walls with the old "fabric" romex, and you know how anal he is about doing things to right to code.

Re: Foam insulation cable derating [Re: mbhydro] #192332
02/08/10 02:46 PM
02/08/10 02:46 PM
K
KJay  Offline
Member
Joined: Nov 2007
Posts: 763
MA, USA
As far as I can tell, the derating requirements of 334.80 only apply to more than two NM cables with two or more current carrying conductors if you don't maintain spacing.
IMO, since the spacing is not defined, it could be 0 to 1mm or even 10-feet... there is no specific distance required top to bottom, or side to side, whether thermal insulation is involved or not. Likewise when any number of NM cables is installed through the same hole in wood framing whether it is to be draft stopped or not.
So, I guess if you have metal framing... no worries?

The way I see it, you could drill a single 1-1/4-inch hole in a wood top plate and run as many NM cables through it as will fit without derating, as long as the cables are evenly stacked top to bottom and side to side. There also doesn’t appear to be anything preventing you from changing direction of the cables to a different position once they pass thought the hole in the framing, as long as they all transition in the same direction with the same spacing, which in this case, could be any desired amount.

I don't write it... I just read it.

Page 1 of 2 1 2

Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
RH1
RH1
California
Posts: 22
Joined: August 2009
Show All Member Profiles 
Top Posters(30 Days)
Admin 21
sparky 15
Potseal 15
Popular Topics(Views)
243,602 Are you busy
180,416 Re: Forum
170,873 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.021s Queries: 16 (0.004s) Memory: 1.0266 MB (Peak: 1.2070 MB) Zlib enabled. Server Time: 2018-01-23 23:51:47 UTC