What type of conductor for conduit filled with water?

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jmjr55

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Telford, PA
We just removed #2 wire that was marked THHN/MTW/THWN. The conduit is underground and filled with water. The A phase was burned through, and the normal load is about 12 amps per leg @480v 3 phase. I thought any conductors marked with a W in the insulation type is rated for water? Does anyone have experience with a similar situation and what type wire held up? Also the wire that we pulled out is about 100 feet long and only 5 years old.
Thanks for your input.
John:
 
I'm surprised it failed. Normally I would install XHHW in that situation, but I've also installed plenty of thhn/thwn in water filled conduits without failure as well.
 
more info ??

more info ??

I agree with the other guys. Certainly can't blame the failure on the water. But my curiousity has me. What application #2 wire, 12 amp load ?? 100 ft run.
I ask because the "devil may be in the details" and we are overlooking some clue as to the failure.
 
augie47 said:
....But my curiousity has me. What application #2 wire, 12 amp load ?? 100 ft run. .....
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I would have guessed parking lot lights, but #2 is overkill for a 100' run unless that 100' is between two pole bases.
 
jmjr55 said:
We just removed #2 wire that was marked THHN/MTW/THWN. The conduit is underground and filled with water. The A phase was burned through, and the normal load is about 12 amps per leg @480v 3 phase. I thought any conductors marked with a W in the insulation type is rated for water? Does anyone have experience with a similar situation and what type wire held up? Also the wire that we pulled out is about 100 feet long and only 5 years old.
Thanks for your input.
John:
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W stands for WET locations. Wet does not mean submerged. Any organic insulating compound is permeable to water, it is just a matter of time before they fail. That is why underground cable installations use inroganic - read metallic - continuous sheet such as lead or corrugated bronze or aluminum such as CLX. Of course you can install others, but expect it to eventually fail.

When you pull into conduit, you never know if inside the conduit you have insulation that is gouged, but with water present you will soon find out.:grin:
 
weressl said:
W stands for WET locations. Wet does not mean submerged.
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Do you have anything to back that up?

IMO Type W is rated for submerged.

In my area almost all underground raceways are full of water.
 
weressl said:
W stands for WET locations. Wet does not mean submerged.
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Sometimes they are one and the same. I don't believe the NEC would allow THWN in raceways underground if that were the case. Raceways often get water in them.
 
iwire said:
Do you have anything to back that up?.
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That W stands for wet, and that T stands for thermoplastic, and that X stands for crosslinked?

IMO Type W is rated for submerged.
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Look at 110.20 to see the differentiation between the different level and methods of water exposure. Unfortunately the Code does not give a defeintion to what it consdiers "wet".
In my area almost all underground raceways are full of water.
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I agree. Could it be that - gasp - the Code is IMPERFECT?!
 
Take a look at the definition of "Location, Wet" notice it says 'locations subject to saturation with water'.

Then as take look at 680.56(B) cord immersed in or exposed to water shall be extra hard usage type w.


Let me spin it around, can you point to a conductor that is actually rated submerged?
 
In my area almost all underground raceways are full of water.
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Same here and we only get 7" per year.

Condensation?



My guess is that they get damaged during installation and eventually fault. Not uncommon at all.
 
Question for the OP:
Is there any chance the water is freezing?

That's a real problem up here. As already mentioned, underground conduits get water in them. I have anecdotal evidence for two different failure modes when the water freezes - at least for smaller conductors, say 10s or smaller.

1. What we found: When you pull the conductors out, the insulation will have a couple of mangled spots. One of the spots will have a black mark.
What happened: 480V circuit fails in the winter. Thaw the conduit with a pipe thawing machine or welding machine till you can blow air through it. Suck out water with a vacuum. Replace conductors.
What I think caused: Water freezes. Smashes the insulation. Insulation eventually gets a hole in it and shorts to conduit.

2. What we found: When you pull the conductors out, one or all conductors will be stretched thin over a 1' to 2' area - 10s pulled down to 14s. The insulation will be pulled in two leaving bare wire.
What happened: 480V circuit fails anytime of year. Thaw the conduit if winter. Suck out the water. Replace conductors.
What I think caused: Water freezes in two different spots a ways apart. Expansion (?? maybe - don't know what else) pulls on the conductors stretching them out thin. Eventually insulation separates and shorts to conduit.

carl
 
iwire said:
Take a look at the definition of "Location, Wet" notice it says 'locations subject to saturation with water'.
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Saturation and submerge are two different and distinct words with different meaning. The example given clearly indicates that the water exposure is periodic and that the item will be dry between.

Then as take look at 680.56(B) cord immersed in or exposed to water shall be extra hard usage type w.
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Loose wording of the Code.


Let me spin it around, can you point to a conductor that is actually rated submerged?
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Not a conductor, but cable. It is called submarine cable, or well cable.
 
weressl said:
Saturation and submerge are two different and distinct words with different meaning. The example given clearly indicates that the water exposure is periodic and that the item will be dry between.
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We will remain in disagreement, it ain't worth arguing about.



Loose wording of the Code.
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?

Or perfect wording.

Not a conductor, but cable. It is called submarine cable, or well cable.
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Can you find it in 310.13 or 400.4? Because if it is not in those tables I can not use it.

BTW, often 'well cable' is unjacketed. :)

pump-wire-reel.gif


I can't use that either, it's not in the NEC.
 
weressl said:
Saturation and submerge are two different and distinct words with different meaning. The example given clearly indicates that the water exposure is periodic and that the item will be dry between.

Not a conductor, but cable. It is called submarine cable, or well cable.
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Let's not loose sight of the fact that the OP said the cable failed after 5 years. I really don't think that thermoplastic will disintergrate after 5 years. I have seen TW wire used as well cable for years- 20 years or more. The pumps fail before the wire does. I just don't see how the submerged makes a difference.

Carl, your point is well made. Freezing inside the pipe makes the most sense.

BTW. The wire bob shows , I believe , is TW
 
After only five years, it could have been damaged during installation, and/or the water has something caustic to the conductor installation that may have caused the failure. It would be nice to see the conductor.


Here is a length of EMT that split due to freezing.
EMT_splitfrombeingFrozen1.jpg


EMT_splitfrombeingFrozen4.jpg
 
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iwire said:
Do you have anything to back that up?

IMO Type W is rated for submerged.

In my area almost all underground raceways are full of water.
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i love it when we have to blow strings into manholes. the helper goes in the other manhole or transformer pad and i blow the string in. usually i can tell when he gets the string because he screams because of the water shooting out. pretty funny sometimes.
 
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