megger readings

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G.E.Sparky

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Just ran URD 350 mcm wire with 4/0 neutral in sched. 40 to residential service. Its a 200 amp underground service 500 feet long through a swamp. I megged it with my meter at 1000v and got a reading of 114 megaohms phase to phase. 97 meg phase to neutral. Then 27 meg other phase to neutral. should I be worried. The conditions were very wet and it was raining. When pulling through --mud came through with wire but none of jacket looked even a bit scratched and it pulled really easy through the 4" sched. 40. What do you guys think?
 
Were both ends of the terminated wires clean? With that high a reading you might be looking at surface conduction on the outside of the insulation.

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Was the wire new on the spool when you pulled it in? If so, I would not be happy with those readings.
Also, as golddigger mentioned, were the ends of the cable clean and dry when you performed the test? If not, then I would make sure the cable ends were clean and dry, and test again.
 
Mmmm. Ends could of been dryer it was pour'n rain. A little muddy. Ends were still in ditch location at the foundation, it's not yet ready for meter can. Will try again with clean ends in a day or two when weather gets better. Also, yes it was one straight pull. Excavator walked it back.
 
G.E.Sparky said:
Mmmm. Ends could of been dryer it was pour'n rain. A little muddy. Ends were still in ditch location at the foundation, it's not yet ready for meter can. Will try again with clean ends in a day or two when weather gets better. Also, yes it was one straight pull. Excavator walked it back.
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I would bet clean ends will solve the issue. It does not take much water and mud on the end of the cable to get a low reading.
 
G.E.Sparky said:
Just ran URD 350 mcm wire with 4/0 neutral in sched. 40 to residential service. Its a
200 amp underground service 500 feet long through a swamp. I megged it with my meter at 1000v and got a reading
of 114 megaohms phase to phase. 97 meg phase to neutral. Then 27 meg other phase to neutral. should I be worried.
The conditions were very wet and it was raining. When pulling through --mud came through with wire but none of jacket
looked even a bit scratched and it pulled really easy through the 4" sched. 40. What do you guys think?
Click to expand...


i wouldn't worry about it... depending on which meggar you were using, that's a lot of capacitance in that wire,
and mud slurry in the pipe makes a pretty fair addition to the capacitance... and it takes just a bit of water
on the ends of the pull to really make it leakdown.

if i was meggering something like that with a small fluke handheld DVM/MEGGER like i have, it'd probably take
4 or 5 minutes to charge it up, and the initial reading would be low..... did you let it sit there until it had finished
soaking the dielectric and the megohm's had stopped climbing?

who'd be a good person to ask would be zog.
 
petersonra said:
Do you guys test the wire on the spools first when you have to do megger testing?
Click to expand...

For other than shielded conductors, will that really tell you anything? You could have an inch of insulation missing, assuming it is not touching another spot with missing insulation, and the wire on a clean dry spool will show infinite on the megger.
 
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