What is the difference between THWN & THHN wire?

Reply

  #1  
Old 05-12-07, 07:26 PM
Member
Thread Starter
Join Date: Apr 2007
Posts: 31
Question What is the difference between THWN & THHN wire?

Just wondering what is the difference and what is better for my different applications.
Thanks.
 
Sponsored Links
  #2  
Old 05-12-07, 08:10 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,802
W indicates sutiable for use in wet locations.
 
  #3  
Old 05-12-07, 08:19 PM
nap's Avatar
nap
nap is offline
New Member
Join Date: May 2006
Location: north
Posts: 4,163
most thhn wire is dual rated as thwn.

check to be sure the wire you purchase is so.
 
  #4  
Old 05-12-07, 08:29 PM
ddr
ddr is offline
Member
Join Date: May 2006
Location: New York City
Posts: 133
THHN is a code for heat-resistant thermoplastic wire which is allowed for use in dry to damp locations and rated for a maximum temperature of 90C (194F).

THWN is a code for heat- and moisture-resistant thermoplastic wire which is allowed for use in both dry and wet locations but has a lower maximum temperature rating of 75C (167F).

As nap said, wire can be dual rated (THHN/THWN). Be careful not to misread the code as there are similar ones for different type wires (such as THHW) while others have suffixes (such as -2) which change the wires rating.
 
  #5  
Old 05-12-07, 09:33 PM
Member
Thread Starter
Join Date: Apr 2007
Posts: 31
So if the wire is dual rated thhn thwn is it usually 75C or 90C and/or is it

the temperature usually also indicated on the wire?
 
  #6  
Old 05-13-07, 03:20 AM
nap's Avatar
nap
nap is offline
New Member
Join Date: May 2006
Location: north
Posts: 4,163
I don't recall seeing a temp rating on the wire I generally use although it could be. Never really paid that much attention to it. I'll have to take a look.

The temp rating I have is within the NEC.
 
  #7  
Old 05-13-07, 04:18 AM
Member
Join Date: Apr 2006
Location: New Bern, NC
Posts: 1,623
"So if the wire is dual rated thhn thwn is it usually 75C or 90C and/or is it "

If the wire is duel rated it can be used at 75 c if used in a wet location or 90 if used in a dry location.

THHN/THWN-2 can be used at the 90 deg rating in a wet or dry location.

Keep in mind that the 90 deg columb is rarely if ever the final amp rating for a given wire size. In DIY work, it will likely never be the final amp rating of the wire. The purpose of the 90 deg columb is for a starting point when doing bundling, ambient temp, etc calculations.

If running conduit and individual conductors, most of the time the limit will be the 75 deg columb, as the lugs on the equipment will only have a 75 deg rating.

If running NM or NMB cable (romex) the limit will be the 60 deg columb, regardless of the wire type.
 
  #8  
Old 05-13-07, 05:32 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,802
Apologies in advance for slightly hijacking this thread but is dual rated acceptable for over head (in air) use to supply power to another structure? (Four # 10 suppling a 30 amp sub panel for example.)
 
  #9  
Old 05-13-07, 10:32 AM
Member
Join Date: Apr 2006
Location: New Bern, NC
Posts: 1,623
duel rated just means rated for more than one thing. If the wire is duel rated for thhn/thwn, then no not for overhead wiring. If the wire is duel rated for overhead and something else then yes.
 
  #10  
Old 05-14-07, 09:56 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,337
Ray,

Overhead wiring must carry a UV/sunlight exposure rating which THHN/THWN does not have.

Overhead wires must also be supported by a load-bearing messenger wire which is only included in the triplex/quadplex cable assemblies that are sold for overhead services.
 
  #11  
Old 05-14-07, 12:45 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,802
ibpooks, thanks for figuring out my somewhat unclear post. (I left out THHN/THWN). So I'm assuming the way I learned with individual conductors fastened to individual insulators is no longer permitted.

I assume if you were running to a garage with other metallic pathways you'd need a four wire cable assembly. I doubt fourplex even exist when you get down as small as #10, correct? Dang, didn't want to go the burial route.
 
  #12  
Old 05-14-07, 03:03 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,337
> I assume if you were running to a garage with other metallic pathways
> you'd need a four wire cable assembly.

Yes. It's highly recommended anyway.

> I doubt fourplex even exist when you get down as small as #10, correct?

The smallest I've seen is #2 aluminum which is rated for 100A as a dwelling feeder. In any case, I hardly ever recommend feeding an outbuilding with anything less than #2 aluminum.

If you really want a smaller feeder, I know the power company uses #4 aluminum, so you might be able to get your hands on that somewhere.
 
  #13  
Old 05-14-07, 04:42 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,802
Thanks all. Guess I'll have to dig.
 
  #14  
Old 05-16-07, 02:30 AM
Member
Join Date: Apr 2006
Location: New Bern, NC
Posts: 1,623
I think anxiter wire and cable or windy city both sell retail.

Let your fingers do the walking. if a wire is made, those two companies can get you some.

Quadplex is fairly common, but as stated not in smaller sizes.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'