Thhw or thwn failure in wet conduit

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rib

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I want to run 4-#10 wires in conduit underground for about 70 feet. I have got recommendations for both for various reasons. I would like to know from your experience which of the two has failed less in a very wet location to the point of water in the conduit. xhhw is also a popular choice. Thanks.
 
I've always used THHN/THWN with no problems. I once pulled some out that had been sitting in water for years. What was soaked had turned brown, but no failure (yet).
 
I've pulled several years old THHN/THWN #10's out of waterlogged conduits that were discolored but otherwise OK. A frugal person could have megged them and pulled them back in.

IMO, THHN/THWN #10 stranded or solid is fine for underground conduit applications.

Welcome to the forum.
 
We had to replace several runs of THHN/THWN over the last several months. All submerged in water, but I don't think the water was the cause of failure. The building is at least 30 years old or older. The wires have outlasted a lot of motors!
 
XHHW is a totally different jacket, and not glossy and slick like the "T" series. I know the Big stuff is!(I think that right...)

In a good run of PVC its the enviromental conditions around the conduit, that act on the remaining space.

Condesation, not flowing water is usually what happens here.

I couldn't figure out if this was new or existing.

The minimum amount of joints of pvc might also be a consideration.

I would use a 90? of the end of a stick down in the earth, try to install as direct as you can.

Scope the run if possible, if existing, figure out which way your be pulling
in respect to the bell end, or install the bell ends of PVC toward your best pulling location.
 
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Thanks for the response. I'm putting in a new conduit. I had an adjacant conduit filled with water for a while using thw wire with no problem. I wanted to know if thwn is as good or better then thhw in water.
 
RIB,

THHN has a good rating.

From a practical perspective, do not over bend and crack the insulation.

Pulling a 'kink' into the conduit may do this.
This is a matter of wiring alignment, or "wire abuse by a helper".
I have pulled a run where the helper did not align the #6 wires,
and the insulation pulled off near the head.
We all know that Scraping, Chaffing, and Cracking are to be avoided.

The resulting fractures and cracks in the insulation
may allow the introduction of moister into the wiring.

Hope you like these forums!
We will not life long enough to learn everything, nor make all the mistakes.
Learn from others!

...
 
Rib you may notice that we often veer off topic here a little, but does anyone know why the plumbers can install pvc underground and are fairly successful at keeping water IN while we can't seem to keep water OUT?
 
Minuteman said:
Rib you may notice that we often veer off topic here a little, but does anyone know why the plumbers can install pvc underground and are fairly successful at keeping water IN while we can't seem to keep water OUT?
Click to expand...

In my opinion one reason is because few ECs seal each end of the conduits letting air pass through the raceway, the water in the air condenses and collects in the low spots.

With normal underground runs it may take years, no one would know. With walk in coolers and freezers I have seen pipes fill with water in just weeks.

I pulled a switch out of a box in a walk in freezer that had only been in operation maybe a week and the switch box looked like some one had filled it with a root beer frozen drink.
 
Minuteman said:
Sometimes, there is a whole lot of condensation goin' on.
Click to expand...

Yes. :smile:

Lets say you have conduits running from an inside electrical room to outdoor locations, often the building is operated under just a bit of positive air pressure, that will send heated, humid air out through all those cool underground pipes 24/7/365 for years on end.

One teaspoon of water a day would be about 4.5 gallons in 10 years.

Of course I do agree sometimes they have been flooded since day one. :D

I think the big issue is no matter how it gets in it finds the low spots and remains forever.
 
iwire said:
Yes. :smile:

Lets say you have conduits running from an inside electrical room to outdoor locations, often the building is operated under just a bit of positive air pressure, that will send heated, humid air out through all those cool underground pipes 24/7/365 for years on end.

One teaspoon of water a day would be about 4.5 gallons in 10 years.

Of course I do agree sometimes they have been flooded since day one. :D

I think the big issue is no matter how it gets in it finds the low spots and remains forever.
Click to expand...

Same thing happens in lot lighting. Despite using solid PVC (as opposed to glued-together 10' sticks, I just can't recall the name for it right now) it will still fill up with water. No flooding. Both ends of the pipe are inside the pole base. Moisture still condenses at both ends during weather (temperature and humidity) changes. I've seen 200' runs of 1" fill up in less than a year.
 
I am finding this forum very helpful. Professional experience appears to be abundant at this forum. Minuteman, interesting way of highlighting the moisture issue. Plumber vs electrician. Good comments from all of your experiences. Sealing the ends of the conduit is a good point. Once condensation has accumulated, have any methods worked at getting the water out without pulling the wires? Where I live (in the mountains) gets 30-50 inches of rain in about 4 months with no rain the rest of the year and 70-90 degree sunny summer weather days.
Back to the topic at hand, is using thw or thhw a solution to the problems with the nylon coating on the thwn, assuming you don't nick the thhw insulation?
 
THWN is pretty much the way to go. As others have said, I have seen wires soaked in "root beer float" stuff and working just fine, only to be removed because of other reasons. (Pump fails, relocate/remodel, etc.) Install the THWN and forgetaboutit. :smile:
 
Maybe a dumb question, but how is the best way to fill the ends which would still allow removal in the future if needed?

Are there any fittings available? Like a gland or cable seal? For multi conductors?

Jim
 
Water or no water, if the THWN is failing in the wet conduits, it was more than likely damaged or compromised from day 1, thus letting the water do its deed.
 
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