cable testing

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transman2

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Is there a way to test a 480V three phase cable via a 500V megg for a phase to ground and phase to phase test without installing jumpers on one end and testing the other end. Trying to test cable for a ground or open leg via a phase to phase loop test. Can testing be done on one end of cable checking the whole cable using a method I'm not familiar with. Just curious!
 
The easiest way is to just leave the load connected and test from the other end. Continuity test checks for "opens" and meggering checks for leakage to ground.
 
Smart $ said:
The easiest way is to just leave the load connected and test from the other end. Continuity test checks for "opens" and meggering checks for leakage to ground.
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Cant do that since its going back to a breaker feeding a Reefer Unit. Want to kill breaker and test cord/cable. Just checking with you high tech people to see if it can be done!
 
transman2 said:
Cant do that since its going back to a breaker feeding a Reefer Unit. Want to kill breaker and test cord/cable. Just checking with you high tech people to see if it can be done!
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I've always done this using the "low tech" method since day one. The handheld meggers.... er-r-r, insulation resistance testers have been a nice improvement, but I don't expect any major improvements in the implementation.
 
Megger

Megger

500 volt megger is to small
test 3 times the voltage with a proper megger and you should have no problem.480 x 3
make sure cable is open at both ends to prevent any safety issues.
 
Twice the working voltage is almost universally accepted. For line to line on 480V use 1000V DC, line to ground use 500V DC.

How you determine the minimum acceptable is up to your local requirements.

As I worked on a lot of old distribution cables I used an old calculation, maximum leakage current not to exceed 1/10,000th of the OCPD setting.
 
I do not see any way of doing an open circuit test with a megger. If you had an open circuit close in to testing end you should see a higher megger reading than the other 2, but this is not conclusive

I amy be missing something here, but for phase to phase shorts couldn't you just put a jumper on the two wires you are not testing and use that as your ground reference for the third? And for phase to ground shorts just test each wire individually to ground? It seems I am missing something here though.

Bohdan
 
A " megger" test is a test for insulation leakage. A continuity test is for shorts, opens, etc. Working from one end doing a megger test phase to ground will tell you if any conductors are leaking to ground. A phase to phase megger test may locate leakage between phases. All can be done from one end as long as the other end is isolated from the load. I don't really understand your question. Readings can be interpreted many ways. Most times if you have a low reading, you can compare it to other phases or similar equipment. A pass/fail reading is not really a standard number. Depends on lots of factors. Most times, though, a meg to ground and phase to phase should be close to infinity if all is well. If all phases read a similar value, though, it's probably OK.
 
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You can easily check insulation resistance from one end. Just put your jumpers on the same end you're testing from. Usually test one cable at a time bonding all others together and to ground.

I don't see a way to do a loop test without a jumper at the other end. You could compare your insulation resistance results and if one has a smaller leakage current it could indicate a shorter conductor and therefore a possible open.

Why can't you setup your test circuit at both ends?

I know you said megger but how about a tdr? That would tell you if you had an open on one leg. Or how about a wheatstone bridge?
 
transman2 said:
Is there a way to test a 480V three phase cable via a 500V megg for a phase to ground and phase to phase test without installing jumpers on one end and testing the other end. Trying to test cable for a ground or open leg via a phase to phase loop test. Can testing be done on one end of cable checking the whole cable using a method I'm not familiar with. Just curious!
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well, open the starter.

use a good ohmmeter, and go phase to phase
on all three motor leads. see if there is any difference
between phases. they should all be damn near identical.

that tells you about the motor windings, and the feeders.

then, put a 1000 vdc megger across one leg, to ground.
this tests the motor, all three feeders, etc. insulation.

hook the motor back up, and run it.
 
Fulthrotl said:
well, open the starter.

use a good ohmmeter, and go phase to phase
on all three motor leads. see if there is any difference
between phases. they should all be damn near identical.

that tells you about the motor windings, and the feeders.

then, put a 1000 vdc megger across one leg, to ground.
this tests the motor, all three feeders, etc. insulation.

hook the motor back up, and run it.
Click to expand...
Motor conductors were not and do not require lifting using this shortened method.
 
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