Is XHHW-2 overkill?

[xguard]

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.

 

[retirede]

It’s likely that everything else will fail or fall apart before properly-applied and installed THWN. Just my opinion.

 

[roger]

There's no doubt that XHHW is the better insulation but I agree with Retired for general wiring applications.

 

[infinity]

I agree with the contractor. Maybe with the exception of underground THHN/THWN-2 will still last a century.

 

[xguard]

Thanks guys!

 

[don_resqcapt19]

I always specify XHHW for underground locations and for the conductors between a VFD and the motor.

 

[electrofelon]

I'm also on the camp that although XHHW is better than THHN, I would put a designer / engineer requiring it in the category of one of those annoying things that they shouldn't worry about or be specifying.

 

[Jraef]

I always specify XHHW for underground locations and for the conductors between a VFD and the motor.

Same here. XHHW is not as prone to “corona breakdown” as the PVC insulation in THHN/THWN is, and more moisture resistant. Putting it on everything is likely overkill, but for sure the critical stuff where it makes sense.

 

[xguard]

I'm also on the camp that although XHHW is better than THHN, I would put a designer / engineer requiring it in the category of one of those annoying things that they shouldn't worry about or be specifying.

Why shouldn't they worry about it or specify it where it provides an advantage?

 

[electrofelon]

Why shouldn't they worry about it or specify it where it provides an advantage?

There are many things that "provide an advantage" : copper over aluminum, RGS 90's, #10 home runs, minimum pipe size. The question is how much of a cost and hassle are these and how large is the advantage. Personally I would prefer these things left to the person actually installing the stuff and with the field experience.

 

[infinity]

There are many things that "provide an advantage" : copper over aluminum, RGS 90's, #10 home runs, minimum pipe size. The question is how much of a cost and hassle are these and how large is the advantage. Personally I would prefer these things left to the person actually installing the stuff and with the field experience.

Me too unless there is some special circumstance these specifications just make it harder to find the materials, sometimes harder to install, and cost more money without any real world benefit. If THHN can last 100 years are you really providing a benefit to the client if you specify something that costs more?

 

[electrofelon]

Me too unless there is some special circumstance these specifications just make it harder to find the materials, sometimes harder to install, and cost more money without any real world benefit. If THHN can last 100 years are you really providing a benefit to the client if you specify something that costs more?

Yeah I feel like this is one of those things that has an extremely low possibility of providing any actual advantage in practice, yet someone looking at bid documents and seeing a specification like this they're going to roll their eyes and tack on money due to the extra hassle.

 

[electrofelon]

I almost always use aluminum conductors, and xhhw is the standard for aluminum so it's sort of a non issue for me. I am mostly designed build.

 

[tortuga]

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.

I have worked with a design team that specified XHHW-2 for those types of municipal projects but only on the outdoor 'article 225' stuff like underground conduits and duct banks etc. I have also used the smaller sizes down to #10 XHHW-2 CU for long outdoor runs to light poles and receptacles on regular commercial.
If its smaller than #10 or Inside a building including under slab I switch to THHN/THWN.

 

[roger]

I know this is a little outside the discussion but to meet the requirements of 517.160 a conductor with the di-electric constant of 3.5, manufacturers of Isolated Power Systems call for XHHW

 

[don_resqcapt19]

I know this is a little outside the discussion but to meet the requirements of 517.160 a conductor with the di-electric constant of 3.5, manufacturers of Isolated Power Systems call for XHHW

Yes, and often prohibit the use of any "wet" wire pulling lubricants.

 

[xguard]

There are many things that "provide an advantage" : copper over aluminum, RGS 90's, #10 home runs, minimum pipe size. The question is how much of a cost and hassle are these and how large is the advantage. Personally I would prefer these things left to the person actually installing the stuff and with the field experience.

I get what you're saying about letting the installer have more say. Honestly, I'd probably lean that way too on some projects. But for critical stuff like pump stations or drawbridges, 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. I see it a lot doing inspections, and I'd just rather not leave crucial details to chance on those kinds of jobs. That said, I do want to identify legacy requirements we specify that may not be as helpful as we thought they were.

 

[steve66]

I'm also on the camp that although XHHW is better than THHN, I would put a designer / engineer requiring it in the category of one of those annoying things that they shouldn't worry about or be specifying.

And most times I would put a contractor that complains about a wire spec as something in the category they shouldn't complain or worry about. After all, nobody made them bid the project Anyhow, many times it's an owner specification, especially with larger clients, so it's not always the engineer driving the bus.

And it doesn't seem like overkill at all for the type of projects the OP mentioned. Especially pump stations and sewage treatment.

But this is the first time I've heard the "harder to pull" comment. I assumed XHHW had the same nylon coating THHN gets, but it doesn't look like the is the case - its required for THHN, but optional for XHHW. And I can't find any XHHW that says it has a nylon coating.

Southwire Simpull XHHW is supposed to be easier to pull, but it still doesn't mention having a nylon jacket.

 

[don_resqcapt19]

And most times I would put a contractor that complains about a wire spec as something in the category they shouldn't complain or worry about. After all, nobody made them bid the project Anyhow, many times it's an owner specification, especially with larger clients, so it's not always the engineer driving the bus.

And it doesn't seem like overkill at all for the type of projects the OP mentioned. Especially pump stations and sewage treatment.

But this is the first time I've heard the "harder to pull" comment. I assumed XHHW had the same nylon coating THHN gets, but it doesn't look like the is the case - its required for THHN, but optional for XHHW. And I can't find any XHHW that says it has a nylon coating.

Southwire Simpull XHHW is supposed to be easier to pull, but it still doesn't mention having a nylon jacket.

I have never seen an outer nylon jacket on XHHW. If you use the correct amount of wire pulling lubricant it pulls just fine, but you don't want any "dry" spots with no lube.

As a side note some XHHW has a nylon wrap around the conductor. I did a project where a factory terminated motor would not run....after some work we found that the nylon wrap had not been removed when the manufacturer made the termination.

 

[electrofelon]

And most times I would put a contractor that complains about a wire spec as something in the category they shouldn't complain or worry about. After all, nobody made them bid the project .

Fair enough, to each their own. I know I am in the minority, but I pretty much only do design build type of work, and it would drive me crazy to install stuff that other people have designed. Yes it's a pet peeve of mine the way the industry is structured where most of the time you have designers or engineers with little to no field experience doing the design and electricians are just installers.