This will be fun.

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Open conductor 1/4 mile of underground in pvc. Only the second I've ever had that was not faulted to earth as well.

Last hope is the POCO meter is open on one phase.

Suggestions welcome.

I have a rarely used TDR but +- 10% is a waste of time generally.

Customer noted lost phase and had power removed by POCO prior to us rebuilding a CF (mess) at the well house.
 

gar

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Location
Ann Arbor, Michigan
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EE
210623-1025 EDT

ptonsparky:

I assume you have 3 or 4 wires in the conduit. I also assume these are individual wires and not a cable. Unfortunately you may not have some equipment that might be useful, in particular an LRC bridge (inductance, resistance, and capacitance).

Can you disconnect all leads at both ends of the run? If this is possible, then you could attempt to measure the capacitance of the open wire to all the other wires from both ends of the conduit.

Because loose wires in a conduit will have capacitance that varies somewhat from one position another the combination of all the good wires as a single conductor gives us a better average measurement. I expect the capacitance per foot may be in the range of 20 to 50 pfd, or about 5280/4 = 1320 times 20 to 50 = 26,400 to 66,000 pfd for the entire cable run. This is 0.026 to 0.066 mfd. If we can assume a complete break, then fairly accurate capacitance readings can be obtained from each end. Probably within 1 %. That would be equivalent to 10 ft.

You might use current flow at a known voltage from each end to estimate capacitance. Some multimeters can measure capacitance and this might be good enough.

Because your break is apparently inside a nonconductive conduit I doubt there is much current flow near the break. Capacitive current flow in the conduit will gradually drop as you go from the input end to the break point. Thus, hard to detect the break point from the magnetic field of the current flow.

I have never tried any experiments where I sent a voltage pulse down a transmission line and looked for that pulse at various points, but if I could get an adequate signal, then I could accurately determine the breakpoint.

Another possibility is to send a moderately high frequency signal down the line and monitor where the signal quits.

.
 

hillbilly1

Senior Member
Location
North Georgia mountains
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Owner/electrical contractor
I have a Greenlee underground tracer that works real well in situations like that. I can usually get within two foot of the break. But if it is in water, makes it much harder to find because of signal bleed.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
I'll post a picture later.
We had one conductor no voltage, two at about 270 to grounded conductor. About 480 between the two.

4 wire system. Bare cu grounded conductor, all in pvc. POCO install years ago.

Two conductors megged at + 1000 meg ohm. One at 11G. Assumed incorrectly that 11g was the open. It was the only good one other than bare cu.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
4F5862E6-68AD-470B-B9C1-FAA0B738D966.jpeg

Thus was the repair we found behind a piece of sch20 that was used as a cover. There is an intact bare cu used as the neutral In the pipe. Each of those two wires megged at over 1000 meg to ground and over 4 meg to each other. One of them was open entirely. The third phase conductor megged at plus 11G.

These wires have been installed Since the late 60s to early 70s. Yes, in pvc. Even so 1000 meg at 1054 volts would normally be a pass if all three were the same.
Point being dry damage as you see here could pass a meg test.

Repairs brought all three phases up to +11G.
We failed to check for an open after the first repairs. We were so sure the problem was in the CF we removed. Not so this time. 2400 feet of #2 Al is about .75 ohms according to my Fluke and an NEC table.
 
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