[RE-wrenches] Underground fault finder

Wed Apr 26 08:25:49 PDT 2023

Dave,

The Thumper creates a high current, high voltage discharge. It uses a massive capacitor bank that you connect to the conductors on one side. When it works correctly, it'll cause a massive arc blast at the location of the fault. Assuming the fault is underground, it'll cause a big thumping sound. One technician walks as close to where he heard the thump as he can guess, then the other tech fires a second thump. The walking tech then readjusts his location and so on until it seems that he's right above where the thumping sound is coming from. Once that's determined to the best of your ability, you mark that spot and dig there. The wires will be all melted at that location. All the wires in that conduit will need to be spliced.

The thumper can be used for overhead lines too. You want to make sure that the fault isn't in an equipment room... the results might not be pleasant. You also want to make sure that all of the wires are isolated on both sides of the run.

I think that the TDR is a cooler tool (time domain reflectometer)... it'll give you an estimated distance (in terms of feet of wire) to the fault location. These two tools are actually best used together... use the TDR, and if it says the fault is 100 feet away, and you have a 200 foot run, then you'd know to position your tech as close as you can to the 100 foot mark, then use the thumper, and you can more quickly determine the exact location to dig. If the TDR says that the fault is at 200', and you only have a 200' run, then you know that it might be more risky to use the thumper, and you can go to the far side of the run and try to find the fault from that side.

I don't have the hands-on experience with either of these tools, but I've read a lot about them. The TDR should be able to detect most faults including a complete sheering of the line. It works by sending a pulse and reading the capacitive and inductive reflections. Whenever there is a splice, a short circuit, or an open circuit, it will send back a reflection and each different type of issue has a different type of reflection. The primary fault that it may not be able to see is a high resistance short circuit (like insulation breakdown or like a high Ω IRT), so it may not help find an intermittent ground fault.

Thanks,
Kienan

Green-Go Solar Distribution LLC

Maxfield Solar LLC (installation and consulting company)

maxfieldsolar at hotmail.com<https://maxfieldsolar@hotmail.com/>

(801) 631-5584(Cell)

distribution.solar

________________________________
From: RE-wrenches <re-wrenches-bounces at lists.re-wrenches.org> on behalf of Drake Chamberlin via RE-wrenches <re-wrenches at lists.re-wrenches.org>
Sent: Thursday, April 20, 2023 4:04 PM
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Cc: drake.chamberlin at redwoodalliance.org <drake.chamberlin at redwoodalliance.org>
Subject: Re: [RE-wrenches] Underground fault finder

The thumper sounds like the one to use, but what does it destroy? Does it induce a much higher voltage on the line than regular line voltage? We are dealing with open circuit problems.

We can return to our original plan of digging up areas and checking for voltage on the lines with a voltage sensor.

Thanks,

Drake

Drake Chamberlin

Athens Electric LLC

Ohio Electrical Contractor’s License 44810

CO Master Electrician’s License 4526

NABCEP Certified PV Installation Professional

---

On 2023-04-18 12:04, Brian Mehalic via RE-wrenches wrote:

Not sure about rental sources in your area, but there are two options:

1) An underground cable fault locator, aka a "thumper," which only works on direct buried cables. It is a destructive test (at the fault location), and should only be performed when there is a known fault in order to locate it. It requires "walking" the cable run with a sensing device to hear the "thump" generated by the high current/high voltage induced on the line.

2) A time domain reflectometer (TDR), which is sort of like radar in that low energy signals are reflected by changes in cable impedance; it is non-destructive, but also not as accurate in terms of the location (providing a cable length to the fault, rather than a "thump" at the actual fault location) and typically cannot see higher resistance (≈>200 MΩ) faults that the thumper can.

Brian Mehalic
NABCEP Certified Solar PV Installation Professional™ R031508-59
National Electrical Code® CMP-4 Member
(520) 204-6639

Solar Energy International
http://www.solarenergy.org

On Tue, Apr 18, 2023 at 8:27 AM Matt Sherald via RE-wrenches <re-wrenches at lists.re-wrenches.org<mailto:re-wrenches at lists.re-wrenches.org>> wrote:
Hi Drake,

I've rented a set-up from my electrical supply house.  I'd check to see if Scott Electric/Advantage Rental serves your part of Ohio.

If memory serves, it is two pieces of equipment that you need.  One to trace the line and a second to find the fault.

-Matt

On Tue, Apr 18, 2023 at 11:20 AM Drake Chamberlin via RE-wrenches <re-wrenches at lists.re-wrenches.org<mailto:re-wrenches at lists.re-wrenches.org>> wrote:
I understand that there is a tool that locates underground faults in
buried cables. No one in our area has one. There are high tech cable
tracers now, but they don't advertise that they can find underground
breaks in wires.

One company online had one that advertised that function. The entire kit
came to $5 or $6K.

Does anyone know where one can be rented.

Thank you,

Drake

Drake Chamberlin
Athens Electric LLC
Ohio Electrical Contractor's License 44810
CO Master Electrician's License 4526
NABCEP Certified PV Installation Professional

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