[RE-wrenches] #10 THWN-2

[Kirk Herander, VSE]

Dual rated thhn / thwn complies.  And every reel I've ever bought is dual
rated. I've never seen single-rated thhn.

Kirk Herander
Vermont Solar Engineering
802.863.1202
NABCEP(tm) Certified Solar Installer
NYSERDA-eligible Installer
VT Solar Incentive Program Partner

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Ryan
Mayfield
Sent: Friday, July 23, 2010 3:31 PM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] #10 THWN-2

Peter,

There was a change in the 2008 NEC (I know - CA is just getting to this Code
cycle) that won't allow THHN inside conduit when the conduit is installed in
wet locations, 300.9 (300.5 for underground):

300.9 Raceways in Wet Locations Above Grade.
Where raceways are installed in wet locations abovegrade, the interior of
these raceways shall be considered to be a wet location. Insulated
conductors and cables installed in raceways in wet locations abovegrade
shall comply with 310.8(C).

And 310.8(C):

(C) Wet Locations. Insulated conductors and cables used in wet locations
shall comply with one of the following:     
(1) 	Be moisture-impervious metal-sheathed 
(2) 	Be types MTW, RHW, RHW-2, TW, THW, THW-2, THHW, THWN, THWN-2, XHHW,
XHHW-2, ZW 
(3) 	Be of a type listed for use in wet locations


So for an attic run, it wouldn't be considered a wet location but for the
outdoor runs it would be. And since so many runs will be exposed to both
types of locations, it only makes sense to me to keep it all THWN-2. I like
your position of only stocking one wire type to reduce the possibility of
confusion in the field.

Ryan




-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Peter
Parrish
Sent: Friday, July 23, 2010 11:28 AM
To: Allan at positiveenergysolar.com; 'RE-wrenches'
Subject: Re: [RE-wrenches] #10 THWN-2

Just a minor point: the dash-two appendage brings a wet-rated wire from 75
deg C to 90 deg C. 

If you are not in a locale that argues for wet-rated wire and your specific
application does not argue for wet-rated wire, IMHO it is perfectly
acceptable to use THHN wire (90 deg C rated for damp environments) for
outdoors, attics and other extreme temperature conditions. Of course you
have to use good 3R boxes and rain-tight EMT connectors.

For us, it is easier to purchase and inventory just one wire type for
conduit runs, and we usually get the same price for THWN-2 as we do for
THHN, or close enough. In fact we almost never use #12 either for the same
reason.
 

 

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