Testing underground wire for short to ground or damage

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rotax

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I might have damaged my UF wire when I buried it in my trench. I would like to test it somehow to see if any of the conductors are exposed to the dirt before I finish burying the rest of it and hooking up a new pump to it.

I tried a simple digital multimeter ohms test with one probe on conductor and one probe pressed into the dirt. The meter would briefly show a megaohm value then go to infinity. Not sure if this is a proper test method at all.

Am thinking of unrolling the rest of the wire, putting a cord plug on the end and a light bulb or other load at the other end (well cap). Plug it into a receptacle and/or ground fault cord adapter to see what happens.

Also thinking of how an electric fence charger might be utilized to test things out, too.
 

Valveman

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You need a meg ohm meter or at least one that does RX100K ohms. Submerging the wire in water to do the test is best. If it then shows no continuity between the wires and ground it is fine.
 

Reach4

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It is possible that if your meter is sensitive enough, the reading could have jumped to non-infinite due to stray capacitance. To test for that, reverse the meter test leads. If you get a jump each time you do that, that tiny bit of capacitance would explain it.

A megger uses much higher voltage to test for leakage... over 500 volts. So your multimeter will put out less than 10 volts, and maybe less than 2 volts.
 

rotax

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Will look around to see if I can borrow a Megger. Doesnt appear that Sunbelt rents such a device.
 

wwhitney

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I tried a simple digital multimeter ohms test with one probe on conductor and one probe pressed into the dirt. The meter would briefly show a megaohm value then go to infinity.
That behavior is expected--the ohmmeter is trying to determine the resistance by passing a small current (from a fixed voltage source), and the displayed resistance reflects the observed current flow. When there is a capacitance across the leads, the current will charge up that capacitance and slowly reduce over time. So you get a reading that increases with time until it stabilizes. A megohmmeter will do the same thing.

Knock-off megohmmeters are available on Amazon etc for under $50.

Cheers, Wayne
 
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