Asking for a friend who's not too big on the internet… 😉
Background:
- On a farm. 1000' underground three wire power run to a well. Buried about 3 feet down.
- There is about 200' of three black cables from the barn to a fence post. There there they come above ground and a switch from three black wires to two black and one yellow which run underground from there to the well. (I'll call them B1, B2 and Y for now with Y assumed to be ground/common. (an assumption of intent, not fact!))
- At the barn's circuit breaker panel… 240 volts measured across the wires at a double breaker. 120 volts from each of those wires to ground. These are presumed to be B1 and B2.
- At the "fence post" joint, and at the well… B1 to Y is 120 volts, B1 to B2 is 120 volts and B2 to Y is 0. (i.e. no combination is 240 volts.)
I'm confused by the 120 volts between B1 and B2 an the zero between B2 and Y.
Current theory:
- Y an B1 are good.
- B2 is broken and in contact with wet soil. (I.e. grounded)
Make sense?
He bought an underground wire locator (a TX to attach to one end and an RX you walk with to find the break). So far it has not been too useful in finding where the break is, most likely due to very wet and saturated ground, but when testing the end of the lines, it seems to indicate that B2 is the problem.
Best Answer
First, neutral and ground are not the same thing. Neutral only handles normal current returns. Safety ground handles only fault currents. The two must never be connected to each other except at the service source. Abusing ground as a current return will "work" but defeats its purpose as a safety device. Actually it makes grounds unsafe.
You are fortunate that the long 1000' run seems to be intact. I have no idea what the story is with the yellow wire. Yellow is not legal for neutral (must be white or gray) and is not legal for safety ground either (must be green, yellow with green stripe, or bare... bare is not allowed for aluminum outdoors). Yellow is just another hot wire color. Is it a 3-phase pump? (Breaker will be a triple).
Wires must be the above-mentioned colors natively if they are 6 AWG or below. 4 AWG or larger can be black and then designated with appropriate color tape, shrinkwrap or paint. Wire that large would be reasonable given the very, very long distance.
Fortunately, wells are 240V and do not require neutral. Also fortuantely, ground can be retrofitted via a different route, so if one wire is borked, you can use the other two for hots and bury just a ground wire. You cannot retrofit a neutral wire and you can't abuse ground for neutral. Of course people on farms will anyway, but the animals Will Not Like It.
If it is in metal conduit, that is an acceptable ground path, but non-threaded conduit tends to rust out.
To use your searching tool, you need to disconnect the wires at both ends first. If the wires are left connected to the circuit, it will confuse the signal too much. Also it won't work in conduit, but conduit makes repair pretty easy, unless it's rusted out.
I would disconnect the wires on the supply side, and install a 22k ohm resistor across each of the pairs of wires, one at a time. Then at the other end, test whether the resistance between any two wires is 22k.