megging

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jimbo123

Senior Member
How do you no if underground feeders meg readings r actually low or r a result of being underwater? Cablesalways under water 10 feet down. Can cables be ok? Newer had any issues till someone megged n said they r bad.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
I am guessing you mean Meg Ohms to ground or earth.

They failed.

What are they used for? Type of load. Not that it matters to much.

The load they serve could very well operate but that doesn't lessen the fact the cable insulation is bad and should be scheduled for replacement or repair.
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
Do they wires only pass through the water or do they splice onto something underwater?

If they only pass through, no splices, then I'd say they failed.

I'll tell you though, I do a fair share of megging in wet environments. Often times, condensation on the outside of splices, wirenuts, etc will show a bad reading. So as long as the ends of the wires are dry and isolated and you still show a bad reading, then you know the actual cable has failed, and not the terminations.
 

jimbo123

Senior Member
Was not sure about reading in water. Though watercaused a low reading ingood cable!. Thanks for the help.
 

brian john

Senior Member
Location
Leesburg, VA
Being in water will have no affect on the insulation readings of a "good" conductor.


How bad are they?

It is not the conductor we are testing, it is the insulation protecting the conductor. (I know you know this it is better the OP understand this).

Insulation in water, aging breaking down the insulation, depending on the chemicals/minerals and with the readings you posted, depending on the system voltage will if you re-energize determine how long the cables will remain energized.
 

hurk27

Senior Member
I have a condo neighborhood, where each house and the club house has post lights with buried UF, last year they had a tree removal company remove some trees by the entrance and damaged some of the cables, well they fixed them by just splicing them and using just electrical tape, I have tried to let me re do the whole mess in pipe, but as with many don't want to spend the money, so there having me meg them and only fix the ones that show below 2 megs, what is funny is I have one tripping the breaker but only reads 2.7 megs, the only way I can explain it, is carbon flash-over, there must be enough carbon tracking that any transient voltage spike will cause a flash-over into a fault, now a 1kv or higher megger will probably show this cable as a fault, but the one I have is only a 500 volt megger.
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
I have a condo neighborhood, where each house and the club house has post lights with buried UF, last year they had a tree removal company remove some trees by the entrance and damaged some of the cables, well they fixed them by just splicing them and using just electrical tape, I have tried to let me re do the whole mess in pipe, but as with many don't want to spend the money, so there having me meg them and only fix the ones that show below 2 megs, what is funny is I have one tripping the breaker but only reads 2.7 megs, the only way I can explain it, is carbon flash-over, there must be enough carbon tracking that any transient voltage spike will cause a flash-over into a fault, now a 1kv or higher megger will probably show this cable as a fault, but the one I have is only a 500 volt megger.

Hurk, I've had a couple tests show full scale at 500 volts and then almost zero at 1000 volts. So sometimes having that 1000 volts will make/break it.
 

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
Do a dielectric breakdown test, then you'll probably get a cable replacement job out of it. Just make sure Dateline isn't watching with hidden cameras :roll:

Kidding of course.......:)
 
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