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I have an underground 240V circuit that the two hot legs are both broken, and the neutral is still intact. I have verified this with a meter. I need to find the location of the break (or burnout) so it can be repaired. I don't want to trench for a new cable because there are many other water lines and wires for a irrigation system in this area of yard. I tried a method I saw on youtube which involved using a wire connected to a lawn mower and to the underground wire and picking up signal with a portable AM radio. It works, but even thoug I had it connected to one of the broken wires, the signal bled over into the intact wire and continued to be picked up by the radio. I would like to know if anyone knows if a signal tracer available on Amazon such as the Noyafa NF-816, or something similar, would work, or would the signal bleed over through the intact wire.

  • Has there been any landscaping or digging, new fence, in the area in question? – JACK Apr 7 '20 at 20:42
  • Is there a part of the yard that has been driven over with vehicles around the time of the break? Is it a 4-wire feed? Is it buried to mandatory depth (24" for direct burial)? – Harper - Reinstate Monica Apr 7 '20 at 23:31
  • The trenching for the irrigation pipes and control wires was done about 13 yrs. ago, and I suspect that they may have nicked the line or may have cut and repaired it. But these trenches crossed the underground electric cable in several places. – mack R Smith Apr 8 '20 at 0:19
  • ...When we advise using conduit, this is one of the reasons why we do. – Ecnerwal Apr 8 '20 at 13:01
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You need a cable locator this is very much like a wire tracer but it uses the ground as part of the circuit. You transmit a signal over the cable and the signal returns through the ground to your receiver.

You normally use it to trace where a cable is located but you can use it to find a break in the cable as the sound will drop out suddenly where their is a break in the cable.

https://www.youtube.com/watch?v=PP_-TEKMNXc

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    Signal tracers like this can be rented from most rental stores. They do work very well I have several models 1 for walls and one that will detect to +4’ prior to purchasing I used to rent for the sub surface but for a pro an hour to the rental place and back plus rental will pay for one quickly. You may find a used one on line also. + – Ed Beal Apr 8 '20 at 13:55
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The short/open test set ECT3000 is not always giving enough information to find the location in case of interruptions. Maybe it is similar to the Noyafa.

An alternate option is a reflectometer. Maybe a test set could be rent for 1 hour.

A (digital USB-connected-) oscilloscope may also work. It has a rectangular waveform generator, whose signal can be fed into the cable. The time lag of the echoed signal gives the distance to the interruption (factor 2 is involved).

Either measurement should be done from both sides.

But the light/signal speed can be different from the vacuum light speed. The cable manufacturer should be able to provide that info.

Or a measurement with a second identical straight cable could serve to measure the speed.

See reflectometer https://en.wikipedia.org/wiki/Time-domain_reflectometer

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    Or if you check from both sides and compare, you should be able to locate the break without knowing the signal speed. This is assuming there is a single break only. – DoxyLover Apr 8 '20 at 0:04

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