Wouldn't you go to the manufacturer for their specs? I've never thought of derating based on 105?,125?, or even higher.
XHHW-2 vs THHN Wire
- Thread starter stuartdmc
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Wouldn't you go to the manufacturer for their specs? I've never thought of derating based on 105?,125?, or even higher.
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
I may simply be misunderstanding the questions; if so, my apologies. Section 310.15 (A)(1) permits ampacities for most ?common? conductors to be computed by 310.15(C) (even with ambients over 90C) under engineering supervision. Tables 310.18 and 310.19 apply to conductors rated above 90C.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
You didn't understand -- we missed that table. :thumbsup:
Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
I love that it's lighter and is much easier to terminate but I HATE installing it in conduit. I can push 500 superslick copper through underground conduits one at a time for short runs no problem. Aluminum, no way in hell. It's going to drag and rub like crazy. It's a love/hate thing with aluminum for me.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Apparently there is copper XHHW also. I have never seen it
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I did not miss it, there is no XHHW listed in those tables so I did not mention them. The whole deal here is that it was mentioned that XHHW can be used at higher temp than THHN, yet all the ampacity tables give them the same rating.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
curt swartz
Electrical Contractor - San Jose, CA
- Location
- San Jose, CA
- Occupation
- Electrical Contractor
It's not the insulation. It's the difference between the copper and aluminum. Take a piece of copper wire and bend it 90 degrees. When you let go it will spring back to almost straight similar to a fish tape. Try the same thing with aluminum and it has very little spring back. I have never used much aluminum in raceways but on the projects I have it has been much harder to pull than copper.
curt swartz
Electrical Contractor - San Jose, CA
- Location
- San Jose, CA
- Occupation
- Electrical Contractor
Back when the high tech companies in silicone valley were building like crazy most of them required copper XHHW for the feeders. My primary supply house had to stock all sizes in both insulation types since the XHHW is more expensive than the THHN/THWN. That seems to have changed now and instead they are using THHN in colors. My supplier now stocks most sizes through 600 in 9 colors. I don't know what made the change in requirements back to THHN. Maybe cost or maybe just a new batch of engineers?
Like the others here I always felt the XHHW insulation was more durable. My supplier said they had more problems with damaging the XHHW when running it on to the Wemcos than they did with THHN.
That "press release" appears to be written by "Distributor Wire and Cable" who I assume is a cable distributor. So we have to take it with a little salt, especially when they are recommending a more expensive product.
I don't think they meant to outright misrepresent the product. Even though THHN and XHHW wire have the same NEC ratings, I think XHHW insulation probably does hold up better at higher temps. So if you install the two products under the same conditions, and operate them at the same currents, in 50 years, the XHHW insulation will probably be in better shape than the THHN insulation. That's what I think they intended to say.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I thought the question was generic and not about XHHW--
Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
I guess I wasn't clear. We get big copper in THHN. We get big aluminum in XHHW or USE/RHW. The aluminum always drags harder than the superslick THHN copper.
I've never tried to get big copper in XHHW, only small stuff like #12 and #10, etc.
Marvin_Hamon
Member
- Location
- Alameda, CA
XHHW is 90?C rated in wet and dry locations where THHN is 90?C rated only in dry locations so they do not have the same insulation temperature rating in the NEC tables once you take the environment into consideration. Since THHN is only rated for dry locations what is available is usually dual rated, like THHN/THWN or THHN/THWN-2. THHN/THWN is rated 90?C dry but only 75?C wet while THHN/THWN-2 is 90?C rated wet or dry just like XHHW. In an outside conduit XHHW is going to have a higher temperature rating.
If the engineer was choosing between XHHW and THHN/THWN for outside conduit then it might have been the desire for the 90?C rating that was the deciding factor for XHHW. THHN/THWN-2 could just as well have been used.
If the engineer was choosing between XHHW and THHN/THWN for outside conduit then it might have been the desire for the 90?C rating that was the deciding factor for XHHW. THHN/THWN-2 could just as well have been used.
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