ECN Forum Forums General Topics of the Trade General Discussion Area Cable Faults

Homer,

Thanks for the clarification. I understand now what you mean. So if what you are telling me is correct, Then I am destroying my cable by "thumping" it looking for the shorts. My local PoCo has come in a couple of times and thumped it for me. When we were doing this we sometimes had to thump it with as much as 10,000 volts DC to locate the fault.

Knock on wood, since I respliced it the last time(Monday), is has run without missing a beat. Hopefully I have finally solved the problem.

Merlin

Gidday there Homer,
Welcome to ECN, mate!.
I must agree with the majority of your comments.
However, one thing has to be said about this cable and it's voltage rating.
Now current ratings are one thing, voltage ratings are another.
Here in New Zealand cables used for 230 or 400V are rated at 600/1000V, that is 600V between cores in the cable and 1000V to earth.
However I would agree with Bob (Iwire), it sounds like you might have got a bad batch.
Moisture in a cable should not cause a problem like this unless there has been poor sealing of the cable and it's cores in past repairs.
Which brings me to another thing, adhesive lined heavy-walled heatshrink is the only thing allowed here at work for jointing cables these days.

Stop thumping....

Use a TDR....( Radar for conductors )

Time Domain Reflectometer.

Trumpy and Tesla--well thought out comments. Moisture and bad cable is no good. And the TDR is a great tool (available from specialty rental agencies for much less money than replacing well thumped cable).
Merlin-good luck on your quest! This site is amazing for it's wealth of experience and ideas-each electrician has many different problems, solutions and experiences to share. What a powerful tool to help get the job done. Many thanks to those who have both organized this web site and also act as moderators.

You might consider two items:
1. If these cables are free they will actually move when high amperage is applied. If this is happening they may damage themselves. If they are not supported often enough they may slap the wall or each other.
2, Since these cables are damp and dirty stray voltages may "walk up" the outside and cause a voltage differential between the outside and inside of the insulation. I have seen this in foundry I worked at.
3. Are the cable run in single phase groupings or are they run with all phases in one group? That might be worth considering.

These cables are run with all phases in a group. I think just maybe I have the problem under control. As of last evening when I checked these pumps, everything was still running good. I think that by thumping, I was just destroying this cable and causing myself undue headaches. I will not thump them anymore.

Thanks to everybody for all the input. You gentlemen are great. The knowledge of this site is unbelievable.

thanks again, Merlin