TROUBLESHOOTING THREE PHASE CABLE
TROUBLESHOOTING THREE PHASE CABLE
(OP)
Hello experts,
I am a past electric motor winder and builder. I just took on a new job in the coal mining industry. The testing equipment supplied is limited. They do not have meggers, hypots or surge testing equipment that I am more comfortable using for troubleshooting at my past job.
I am looking for information in general on troubleshooting
three phase cables with a ohm meter. Readings that would indicate such as phase to phase short, phase to gound short, moisture in cable, open leg etc..
Thank's in advance
kind regards,
THarper
I am a past electric motor winder and builder. I just took on a new job in the coal mining industry. The testing equipment supplied is limited. They do not have meggers, hypots or surge testing equipment that I am more comfortable using for troubleshooting at my past job.
I am looking for information in general on troubleshooting
three phase cables with a ohm meter. Readings that would indicate such as phase to phase short, phase to gound short, moisture in cable, open leg etc..
Thank's in advance
kind regards,
THarper





RE: TROUBLESHOOTING THREE PHASE CABLE
What works for a 9VDC circuit from a VOM has little relation to what problems you will find at industrial volages. Continuity maybe, but cable capacitance can fool you on occasion. The only suggestion I can offer is that when dealing with 3 phase cable systems, you can sometimes spot a problem when there is a big difference in one cable compared to the other two. What you would be reading in terms of number values would otherwise be relatively meaningless however. For you own sanity I would suggest as a minimum, buy your own hand crank megger on ebay and write it off as a tool expense on your taxes next year if you can. I've seen them go for around $50 not too long ago, and they don't require batteries.
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: TROUBLESHOOTING THREE PHASE CABLE
A rule of thumb for #10 AWG is 1 ohm per 1000 feet.
You are not going to localize a fault in a cable by resistance unless you use a wheatstone bridge and use the multimeter in place of the galvanometer, and then the Wheatstone is best on hard grounds or shorts. Because of the low voltage used it is not particularly dependable on high resistance faults.
We have all encountered faults that were voltage dependent. The multi meter reads good, but the equipment fails the energisation test.
What can you do with what you got.
I would look for a small dry type transformer to get full voltage for testing. Better yet twice normal voltage. Even better, 1000 Volts.
Use light bulbs or better yet, resistors and one small lamp to limit the current. You will get a good indication of cable condition by whether the lights are bright, dim or off. Make your test connections and then step away before energising the transformer..
You can use your current range on the multi meter to get a good indication of the resistance of a high resistance fault. Again make the connections and then step aside before energizing.
CAUTION WARNING THIS METHOD IS DANGEROUS
THE ONLY THING MORE DANGEROUS MAY BE USING POWER CABLES WITH NOTHING BUT A MULTIMETER TO CHECK FOR FAULTS.
BETTER YET, Buy your own megger. It's your life at stake.
RE: TROUBLESHOOTING THREE PHASE CABLE
Thanks again guys
RE: TROUBLESHOOTING THREE PHASE CABLE
RE: TROUBLESHOOTING THREE PHASE CABLE
Glad to hear you have a megger. Please now disregard my suggestions and use the megger instead.
Yours
RE: TROUBLESHOOTING THREE PHASE CABLE
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: TROUBLESHOOTING THREE PHASE CABLE
RE: TROUBLESHOOTING THREE PHASE CABLE
Gunnar Englund
www.gke.org
RE: TROUBLESHOOTING THREE PHASE CABLE
RE: TROUBLESHOOTING THREE PHASE CABLE
PS. I visited your article site Gunnar, and I think it is humorous that so many people originally thought it was intructions to build your own RADAR!
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: TROUBLESHOOTING THREE PHASE CABLE
RE: TROUBLESHOOTING THREE PHASE CABLE