Best wire to sit in water "forever"

[grasfulls]

Most every conduit around here fills with water. We have always pulled in THHN/THWN wire, is that the best for longevity / safety?

 

[kwired]

In general the more insulation the better depending of course on if or how water will affect the insulation. Conductors designed for direct burial will usually have thicker insulation than a conductor not intended for direct burial.

Protecting the insulation from damage during installation may be a big factor in how long it will last. Nicks and scrapes may go unnoticed and cause a failure later.

 

[infinity]

IMO XHHW would seem to be a better choice. Not from real scientific data just from using both XHHW and THHN/THWN.

 

[grasfulls]

thicker insulation

thicker insulation

In general the more insulation the better depending of course on if or how water will affect the insulation. Conductors designed for direct burial will usually have thicker insulation than a conductor not intended for direct burial.

Protecting the insulation from damage during installation may be a big factor in how long it will last. Nicks and scrapes may go unnoticed and cause a failure later.

I do not think I have ever seen large wires pulled in with out a few nicks and scrapes, usually just the outer layer of THHN, though sometimes a tad deeper :-(. It does not seem to matter if bell ends are in pull boxes and bushings on either end, somehow they scrape it on something, well, I should inclde "me" in "they"....so "we".

 

[grasfulls]

Xhhw thhn/thwn

Xhhw thhn/thwn

IMO XHHW would seem to be a better choice. Not from real scientific data just from using both XHHW and THHN/THWN.

I am also looking at Type USE-2 (EPR-HYP) and Type USE-2 RHW-2 OR RHH XLP. Both approved for direct burial, is this going overboard? It may infringe on my conduit size, I only installed 4" and need 350MCM copper. It fits into kwired's suggestion for direct burial cable as well.

In general the more insulation the better depending of course on if or how water will affect the insulation. Conductors designed for direct burial will usually have thicker insulation than a conductor not intended for direct burial.

 

[kwired]

I do not think I have ever seen large wires pulled in with out a few nicks and scrapes, usually just the outer layer of THHN, though sometimes a tad deeper :-(. It does not seem to matter if bell ends are in pull boxes and bushings on either end, somehow they scrape it on something, well, I should inclde "me" in "they"....so "we".

I am also looking at Type USE-2 (EPR-HYP) and Type USE-2 RHW-2 OR RHH XLP. Both approved for direct burial, is this going overboard? It may infringe on my conduit size, I only installed 4" and need 350MCM copper. It fits into kwired's suggestion for direct burial cable as well.

The trick is to avoid scraping it THHN/THWN has relatively thin insulation, doesn't take too much of a nick or scrape and you have exposed the conductor. Using a RHW with a thicker insulation and the same nick maybe only gets halfway to the conductor, you still want to avoid scraping it though because this is now a weaker spot in the insulation.

 

[Dave58er]

In this area all underground conduits fill with water as well.

The guys who have talked about nicks and scrapes are right IMO.

I've only seen underground conductors fail due to water one time.
I got sent out to do a service on some remote pumps that were tripping breakers. The wires didn't hold up when megger'd. When the old wires were pulled out you could see that where the plastic on the thhn had been nicked (actually scraped and dragged is a better description) water would get in and discolor and deteriorate the inner part of the insulation.

But really, how often do you guys see wires fail just due water? They seem pretty resilient considering.

 

[kwired]

around here a lot of underground aluminum conductors are installed on farms both direct buried and in raceways, if you damage the insulation you have a weak point for transients from lightning to try to escape the conductor. Once an aluminum conductor has insulation compromised it does not take long and you have total failure of conductor. When you dig up this failure or withdraw conductor from raceway you will have bulging insulation or complete separation with nothing but white substance inside (probably aluminum oxide) Lots of sandy soils around where I live. Sometimes you will find sand that has been turned into glass right next to the conductor failure point.

 

[tom baker]

I have seen THHN/W fail where installed in water filled conduits.
We spec XHHW-2, or XHHW-2 USE for any underground run.
If I recall, the PVC insulation is only 15 mils, it just takes a nick for it to fail.

 

[LarryFine]

. . . you will have bulging insulation ... with nothing but white substance inside (probably aluminum oxide) . . .

Well, of course it is. What else could it be?

 

[iwire]

Another vote for XHHW or RHW/USE

 

[cschmid]

you guys forgot to add that not only do they fill water they freeze solid as well..

 

[ohmhead]

Most every conduit around here fills with water. We have always pulled in THHN/THWN wire, is that the best for longevity / safety?

Well months ago we had a post which everyone said that that was not going to ever happen water can not come in if your conduit was installed correctly ?

And my post telling them that it happens all the time in florida thur pvc conduit you blow it out and the next day its back you just made my day thanks .

THWN -XHHW-2 THHW table 310.13 thats what we use never a problem ever . The only problem is getting a true tape in conduits with water it sticks to the inside wall and drys to the inside walls and never wants to come out again.

 

[iwire]

Well months ago we had a post which everyone said that that was not going to ever happen water can not come in if your conduit was installed correctly ?

And my post telling them that it happens all the time in florida thur pvc conduit you blow it out and the next day its back you just made my day thanks .

Well I think you remember things incorrectly.

Well I think if we go back and look at the thread we will see many said conduits are filled with water.

 

[ohmhead]

Well I think you remember things incorrectly.

Well I think if we go back and look at the thread we will see many said conduits are filled with water.

Well post 7 # did you not say that i was wrong ?

PVC GLUE issue

 

[don_resqcapt19]

you guys forgot to add that not only do they fill water they freeze solid as well..

Freeze thaw cycles are a big issue if metallic conduit or concrete encased non-metallic conduits are used. The ice produces a crushing force that damages the insulation. I tried a number of code cycles ago to require underground conduits be installed like water pipe...below the frost line.

 

[220wire]

I am looking at a job specd with RHW Locomotive cable and type-w multi conductor cable. I've never used RHW loco cable before but the type-w is usually used in mining operations and can be submerged. A "better' conduit if you can use it is HDPE. The POCO use it alot and can come pre-wired

 

[cschmid]

Freeze thaw cycles are a big issue if metallic conduit or concrete encased non-metallic conduits are used. The ice produces a crushing force that damages the insulation. I tried a number of code cycles ago to require underground conduits be installed like water pipe...below the frost line.

That would be so costly but really have no idea on the solution..but if you run the conduit so it all drains one way you could drill tiny hole in the bottom of the 90 and put some pee gravel under it so it would drain..

 

[kwired]

How deep is the frost in some of the far northern states? Here in northern Nebraska if you bury anything deeper than about 24 inches frost will not be a problem. Some years on north side of buildings or areas that do not get direct sun frost may be a little deeper. Many POCO's require service laterals to be 36 inches deep.

I have seen more trouble on buildings that had the backfill around the basement settle and take wiring down than I have seen from frost heave.

 

[kwired]

Had another idea - how about undersizing conductors so they operate at higher temperature - no more frost problems