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Discussion Starter · #1 ·
What is the proper way to eliminate moisture from cables before megging them? These are 750mcm three conductor armored cables carrying 4160.
 

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I don't have the answer. If you don't want to say that's fine. Sorry I can't help
 

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Most electricians would choose NOT to re use wet cables,
Due mainly to legal liability issues,
But if you must ! Leave them out in the sun for at least a week.
 

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Most conductors are rated for moisture. Problems arise when the ends aren't sealed properly and moisture enters between the insulation. How wet did it get, how old is it, what makes you think it's got a moisture issue? All relevant questions. 4160 is nothing to monkey with and is the reason why I asked why you were asking. If it's for a new installation I hope to hell there is someone around who knows this stuff.
 

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Discussion Starter · #7 ·
I am spectating this at my current job. One of the cables isn't megging out and they want to rule out moisture. There was a fault that trashed the line side of a transformer and they are wanting to rule out moisture invasion in the cable. I don't see how this would solve anything though. Once a cable causes a fault it is trash IMHO.
 

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I would get that kind of advice from the manufacture of the cable.
 

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butcher733 said:
I am spectating this at my current job. One of the cables isn't megging out and they want to rule out moisture. There was a fault that trashed the line side of a transformer and they are wanting to rule out moisture invasion in the cable. I don't see how this would solve anything though. Once a cable causes a fault it is trash IMHO.
Is it like a lead sheathed mv cable? Water inside a cable can be responsible for expediting the breakdown of already weak spots in the insulation. Drying a cable out doesn't always make things better though due to the impurities in the water that are left behind afterwards. I wouldn't think that water in a cable could produce a full blown fault but it's hard to say without knowing the type of cable and insulation in question.
 

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Discussion Starter · #10 ·
Is it like a lead sheathed mv cable? Water inside a cable can be responsible for expediting the breakdown of already weak spots in the insulation. Drying a cable out doesn't always make things better though due to the impurities in the water that are left behind afterwards. I wouldn't think that water in a cable could produce a full blown fault but it's hard to say without knowing the type of cable and insulation in question.
Its pretty much teck cable. Plastic coated MC on a large scale. Armored tray cable by any other name.
 

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A cable isn't megging out? Is it overhead, exposed or underground? Maybe it's blown to pieces haha
 

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Discussion Starter · #12 ·
A cable isn't megging out? Is it overhead, exposed or underground? Maybe it's blown to pieces haha
Exposed tray. I think that one theory is that the boot in front of the lug (stress cone?) Has moisture in it and is shorting the phase to ground.
 

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Is it like a lead sheathed mv cable? Water inside a cable can be responsible for expediting the breakdown of already weak spots in the insulation. Drying a cable out doesn't always make things better though due to the impurities in the water that are left behind afterwards. I wouldn't think that water in a cable could produce a full blown fault but it's hard to say without knowing the type of cable and insulation in question.
Im not grilling you, Im just interested in hearing more about the impurities left behind part....
 

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Shock-Therapy said:
Im not grilling you, Im just interested in hearing more about the impurities left behind part....
Pure water is actually an insulator. But pure water (distilled) is not typically what we're talking about when it comes to water damage in a cable. Rain water is formed around dust and pollutants and ground water contains minerals and salts; all of this is still present after the water evaporates and however minimal the conductivity of the material it still can attribute to high resistance faults, especially in mv
 

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I was figuring on the salt deposits likely. Runoff could contain traces of petroleum, I can see where that could be an issue.
 

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Most electricians would choose NOT to re use wet cables,
Due mainly to legal liability issues,
But if you must ! Leave them out in the sun for at least a week.
We pulled in 15kv cables yesterday and the amount of water that came out of the conduit was enough to fill a small pool. The new cables tested out.

The old cables (in a parallel conduit) had been in there for years and were only replaced as it was a job spec for a site upgrade
 
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