Locating fault in buried PVC conduit with 277/480 secondary.

[11bgrunt]

Construction is ten years old. Secondary is 277/480.
Wire size 500mcm cu., single run X 4 conductors plus EGC.
Length is 750', yes 750'.
No pull box in that 750'.
1 phase trips instantaneously and another trips out after a few minutes.
Customer wanted to pull the one conductor out of the conduit and replace that one conductor somehow. Today they are willing to pull the entire run, replace the blown out conductor and repull.
All seems like bad ideas to me.
We want to identify the location of the fault, dig up, cut pipe and wire, then add splice boxes necessary.
With the equipment we have, there doesn't seem to be a good method to locate the fault inside the conduit that would provide enough confidence that we were right before we start digging. At MV we just thump. Our thumper won't get below 4K.
What methods have you seen work? Maybe you can offer other options.

 

[ptonsparky]

Construction is ten years old. Secondary is 277/480.
Wire size 500mcm cu., single run X 4 conductors plus EGC.
Length is 750', yes 750'.
No pull box in that 750'.
1 phase trips instantaneously and another trips out after a few minutes.
Customer wanted to pull the one conductor out of the conduit and replace that one conductor somehow. Today they are willing to pull the entire run, replace the blown out conductor and repull.
All seems like bad ideas to me.
We want to identify the location of the fault, dig up, cut pipe and wire, then add splice boxes necessary.
With the equipment we have, there doesn't seem to be a good method to locate the fault inside the conduit that would provide enough confidence that we were right before we start digging. At MV we just thump. Our thumper won't get below 4K.
What methods have you seen work? Maybe you can offer other options.

We do not have a thumper 'cause we don't work on anything over 480. You need different equipment

Our fault locator will find the fault in a PVC conduit to the nearest crack in the conduit and there usually is one. A lot of times within a short distance of the fault. PVC couplings leak so that can put you within 10'.

A good number of cable locators will follow the signal and drop off as they approach the fault. Look for the drop in signal, mark and look for rise in signal. Mark. Do it from both ends. Fault is between the marks.

Use a TDR.

One thing that screws us is when the POCO had a practice of pulling bare CU as the Neutral conductor. Our fault locator will not work with a degree of accuracy that I will guarantee the spot.

We stagger heat shrink wrapped compression butt splices in the repaired conduit. I know of No farmer that wants to plant or harvest around a couple junction boxes.

Add: Isolate both ends of all conductors.

 

[11bgrunt]

We did locate the wire route with a good locator and with an A frame we found the break under a new concrete sidewalk.
The Contractor that did the water or the concrete for the expansion had dug up the pipe, broke the PVC and damaged the conductors. They made a PVC sleeve to repair the break and covered it up. A year and a half later it finally blows out. I don't know today's cost for the 500mcm but if they are forced to pull a new 750' it will get expensive in a hurry for the crew that broke the pipe.
Both sides of the break had chain link fence to corral the students. I do believe it was all close enough there was a risk of the fence having some voltage on it.