Is XHHW-2 overkill?

[tortuga]

I have never seen an outer nylon jacket on XHHW.

I assumed XHHW had the same nylon coating THHN gets, but it doesn't look like the is the case

That is XHHN I have never seen it but it got added to the code a few cycles back.

especially when we're going with the lowest bid, it just makes me a bit uneasy. You know how 'field experience' can really swing wildly from one crew to the next.

Yeah keep specifying XHHW you might even give more EC's the right idea, I got the idea from a municipal project EE about 20 years ago and started using it occasionaly on commercial design / builds - just for for long outside stuff.
Outdoor stuff is typically longer pulls, subject to harsher conditions generally and during wire pulls more likely to get some dirt or grit in the conduit. Conduits then are more likely to be water logged for months after storm with who knows what in the water, around here I have seen UG conduit just bubble water out of a vault, for the slight cost difference you get a much better install.
Its a easy option to add to a quote even if its not in the specs.

 

[electrofelon]

This may seem to go against my previous posts, but I wish they would just stop making THHN and make it all XHHW.

 

[tom baker]

Not overkill. I worked in all the locations you mention. I saw failures of THHW/N insulation used in underground runs where it sat in water at WWTP. Same on street lighting. Our specs were any runs underground would be XHHW-2. For buildings dry locations specs allowed THHW/N. WWTP, WWLS are critical locations to use XHHW-2. If it’s in the specs that’s what contractors bid on. Hard to pull? That’s what you bid on.

 

[Jraef]

What’s interesting to me is the part of this discussion where people are having trouble finding XHHW… Around here it’s just as common as THHN/THWN in the supply houses, at least those that primarily serve industrial and commercial contractors and users. I guess I’m kind of spoiled…

 

[Birken Vogt]

Why is it that copper wire traditionally comes with THHN and aluminum comes with XHHW?

 

[tortuga]

The other cool thing about XHHW-2 is in the larger sizes perhaps 1/0 and larger its usually 'approved for cable tray use'

 

[electrofelon]

Why is it that copper wire traditionally comes with THHN and aluminum comes with XHHW?

Yeah that's always been the way it is every where I have worked. Always wondered why that is.

 

[don_resqcapt19]

The other cool thing about XHHW-2 is in the larger sizes perhaps 1/0 and larger its usually 'approved for cable tray use'

Most insulation types in sizes 1/0 and larger are marked for CT use.

 

[Ken_S]

I'm a design engineer and typically require XHHW-2 insulation for our projects. These projects ranges from roadway lighting, small pump stations, sewage treatment plants, office buildings, labs, tunnels and the list goes on. From what I've read the XHHW-2 tends to last longer than the THWN-2 and that's why I've stuck with it. All of these facilities are government owned and have been around for 50 plus years and will very likely be there in another 50 years. It's not a dollar general (not to pick on them) that will be open for ten years and then shut down if things don't go right.

With all that said, on most every project the contractor complains about the wire choice. They often say it's more difficult to pull than THWN or their supplier doesn't have it available. Is my choice reasonable or am I just adding unnecessary cost or frustration to these projects? Let me know what you think, thanks.

I worked for a state dot for 20 years, that requirement is often called out in engineering standards from associations such as AASHTO.