Possible Break In Wire

[MAT0926]

I have an underground wire running from my basement circuit panel to my shed in the back yard. The line consists of 12/2 UF-B W/G Cable. I have a GFCI outlet in the basement just before the line exits the house and runs to the shed. Along the way I needed to connect two lines of the same type to complete the run to the shed. I used the standard connecting unit with the shrink wrap ends purchased at the local Home Depot. For ten years this circuit has worked perfectly. Last week the GFCI outlet tripped and wouldn’t reset. I went to the shed and disconnected the line from the first outlet to see if that was the issue. The outlet still wouldn’t reset. I purchased a new GFCI outlet and repeated the same trial and error process that I described above and still the new outlet wouldn’t reset. I inspected the exposed pieces of wire coming into the house and shed and there were no issues. The ground in the area of the run appears to be flat with no noticeable rodent holes/trails. Is there a way to search for a break without digging up the entire run? Am I missing an additional diagnosing tool?

[Jeroen3]

There are devices that use HF and reflections to detect wire breaks and shorts. Like fluke TS100.
Maybe your local electrician has one.

[jeroen79]

How does the GFCI outlet fit into this?

Is it wired like this?
Distribution  panel ->GFCI outlet -> plug -> cable leaving basement -> underground splice -> cable entering shed -> stuff in shed

A break in the cable would not trip a GFCI.
A break in the cable's isolation might.

An insulationresistancetester/megger can tell you this.
Be sure you know how to use it.

Have you disconnected all equipment in the shed to rule out that the fault is there?

Does the GFCI trip when you disconnect the underground cable in the basement?

[SeanB]

Well, very likely the fault is in one of the joins, so you will have to start at the shortest length side and dig back to find the failed one, unless you did mark the cable run and have a diagram of the join location ( always a good thing to have, or at least a direct run so you have a keep out area for gardening and digging)to do only a short dig. Otherwise dig down at the ends for around 10ft and see if there is cable damage there, otherwise it is the join that has failed.

[frahul]

I would recommend you replace the entire line since it has been ten years.

[james_s]

Around here we have a lot of rocks in the soil and it's not uncommon for direct burial cable to fail. You may be able to use a time domain reflectometer to locate the fault, they're normally used for coax and twisted pair but may work on this. If the fault is not at one of the ends though you pretty much have to replace the whole cable anyway. If you run it in conduit, it is unlikely to fail again.

[MAT0926]

Circuit Breaker -> GFCI Outlet -> Cable leaving the basement -> Underground splice -> Shed ...

I disconnected the line into the shed at the first outlet. GFCI Outlet still tripped.

I disconnected the line in the basement leading out to the shed and the GFCI Outlet stayed active.

[james_s]

If there's an underground splice, that's where I'd start looking. I didn't think you were allowed to do that?

[Armadillo]

You can use a 1000v insulation tester to check which of the line is leaked to earth e.g. Yokokawa MY10-05:1000V/2000M? . You can break up the section of the wires into aboveground and underground, so that you determine if the lines going into the earth is actually faulty or above earth portion.

In case you need to buried new lines, maybe economical to run in heavy duty pvc conduits which can last you a lifetime or concrete trenches maybe can sustain some TNT [joking]. Direct buried Underground splicing is normally done by a licensed splicer.