Testing for moisture in wire

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mjmike

Senior Member
Not sure where to post this question, so I will try this forum. I am working on troubleshooting an electrical system and we feel water has entered some wire. I know we should just replace the wire etc. etc. etc. but please lets stick to the question I have.

Question: I am trying to determine if a tester exists or a way to test if water has gotten into a wire. Any ideas?

The wire is stranded and I know water can wick pretty far in this stuff. I have talked to Fluke, Ideal and Extech but no tester exists. I thought of doing a dielectrtic test / insulation test but this won't say if there is / was water in the wire.

thanks
 
zog

zog

Senior Member
Location
Charlotte, NC
mjmike said:
Not sure where to post this question, so I will try this forum. I am working on troubleshooting an electrical system and we feel water has entered some wire. I know we should just replace the wire etc. etc. etc. but please lets stick to the question I have.

Question: I am trying to determine if a tester exists or a way to test if water has gotten into a wire. Any ideas?

The wire is stranded and I know water can wick pretty far in this stuff. I have talked to Fluke, Ideal and Extech but no tester exists. I thought of doing a dielectrtic test / insulation test but this won't say if there is / was water in the wire.

thanks
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It would really help to know what type of wire you are talking about, there are methods like PF/DF testing and N2 purging but just replacing may be cheaper option depening on what you are talking about.
 
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mjmike

Senior Member
The wire is in 600V wire I believe and is stranded copper, possibly thhw/thwn, about #4 in size. Then there is an SO type cord 4-wire approx.
 
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TxEngr

Senior Member
Location
North Florida
It's probably easier to just dry the wire out. I've never heard of a test. I've used dry nitrogen in the past on some 15KV cable but it took a few days to dry it out. I've never tried this but wonder if you could use a welding machine to heat the cable up (just a little) and dry it out - much like you would a motor. However, if it megs good then I'd probably just use it.
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Assuming that the conductor insulation is in good condition and the water entered from the ends of the conductor I don't see an issue. The water just becomes part of the conductor. I guess that if you have enough water and it freezes the expansion of the water as it turns to ice could damage the insulation. The same if you get it hot enough to turn the water into steam, but not too many conductors are suitable for operation at 100?C.

If the water is entering through the insulation itself, then the wire is junk.
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Trick is to keep the water from leaking out the end of the wire onto your connections. Use it for bottom feeds only.

Probably could rig up a strain type cable connector to some couplings and an air hose then apply pressure for a few days or weeks. Probably have to unwind it and lay it flat. Then watch for drips to come out the end.
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
ptonsparky said:
Trick is to keep the water from leaking out the end of the wire onto your connections. ...
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Just tape up the lower end really well:grin:

We did a tear out of some old 2.3kV service conductors a number of years ago and when we untapped the connections at the switch gear bus, about a quart of water ran out of the cables. The cables were in service until just before we disconnected them. They were terminated at the outside connection to the utility with the bare strands pointing up and over time the spaces between the strands filled with water and it stayed there until we let it out.
 
Len

Len

Senior Member
Location
Bucks County
wet wire

wet wire

If the wire is rated for wet locations, they you have no issue. If it is not rated for wet locations you need to replace it.
 
S

SJRibsman

Member
Location
south Dakota
hmm, just a thought, but I have worked on wind genration towers, and my Q, is that if the outer insulation of the stranded four/wire MCM/cable should crack or break due to the coldness of the elements, would this larger product still be allowable for the application, or our we allowed to repair the product, just like we would a break in lets say #12/wire. Just has me thinking that the inner insulation isn't broken around the wire, so maybe the repair would be feasable?
 
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hardworkingstiff

Senior Member
Location
Wilmington, NC
I know you didn't ask this but I'm sharing anyway. I once found water coming into a service disconnect inside of a building. The conduit came up through the floor and the problem was when it rained the disconnect leaked water. Found the neutral at the overhead conductors on the pole (is where the underground conduit went to get power) came out of the conduit and connected to the neutral without a drip loop and the wire was looking straight up. Rain ran into the wire and dripped out in the disconnect. Store owner said it had been like this for years working fine.
 
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rcwilson

Senior Member
Location
Redmond, WA
How to Dry Wet Cables

How to Dry Wet Cables

An old Cablec cable manual had a procedure for drying out cables using dry nitorgen. I?ll summarize.

If it is a high voltage cable, dry the conductor strands separately from the shield wires. (Otherwise the air gets short circuited).

At the upper end of the cable, wrap two layers of HV tape around the conductor to act as a seal. Jam a piece of hose jam on the wire and clamp in place with a hose clamp. Use the appropriate pipe nipples, hose clamps and reducer fittings to connect it up to the nitrogen tank regulator hose. Use tees and valves to tap off to other conductors if necessary.

Fasten a gallon plastic bag around the wire at the lower end with tape. Snip one corner to let the air out.

Put 15-25 psi on the cables for 8 hours or more, maintaining pressure for some time ( 8 hours) after the last moisture is out.

Water vapor is easier to detect if you sprinkle Anhydrous Cupric Sulfate in the bag, about 1 TSP. It?s that stuff that turns blue when it gets wet. It?s available from scientific lab supply houses.

For the size of wires you?re taking about, it may be cheaper to re-pull them.

When I was in the testing business, the only way we could test for water was a megger test. If the water was held inside the insulation, the wire still passed the test.
 
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rcwilson

Senior Member
Location
Redmond, WA
don_resqcapt19 said:
Bob,
Is there any real reason to try to get the water out?
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Because the client wants a dry cable? That's the only answer I can think of for low voltage wiring (<1,000V)

On high voltage cables with cross-link polyethylene insulation there is a failure mechanism called water treeing where the cable insulation develops minute cracks or tracks that lead to cable failure, especially if the a DC high pot test is applied. Leaving water in the strands may lead to water treeing and cable failure. There are products that inject a gel into the cable strands to drive out the water to prolong the life of in service cables. This is an issue on older, direct buried URD cables.

If the client wants dry wires and is wiling to pay for the drying process, it sounded like an interesting thing to try. I doubt that there would be much benefit.
 
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