Finding an underground power cable

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linw

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#309318 8-Oct-2023 08:52

My son in Wellington has a fault in his mains power line that stops it being connected to the power. They know roughly where in the cable the problem is but an electrician dug a couple of holes but couldn't find it.

Is there any way of locating it, say, with a signal put through the cable?

He was quoted $16,000 to put a new cable in!!

TIA.

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#3144210 8-Oct-2023 08:54

Could you use a cable locator?

https://www.kennardshire.co.nz/for-hire/test-measure/electrical/pipe-cable-locator-advanced

RunningMan

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#3144212 8-Oct-2023 08:59

A big part of that quote may be digging and refilling a trench. If your son's able to do that part (if/when needed) then the price may come down quite a bit.

There's also cable locating services who are experts at using the above machines and will come oout to mark all underground services in an area for you.

EDIT: getting someone out may be cheaper and easier than hiring the machine to DIY.

https://www.beforeudig.co.nz/nz/locators/certified-locators-in-nz

larknz

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#3144215 8-Oct-2023 09:32

There are quite a few cable locating companies around who should be able to accurately locate the cable. The difficult part will be finding the fault. Who installed the cable, did they test it at the time of installation? If they didn't do any tests I would put it back on them to fix the fault.

gregmcc

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#3144220 8-Oct-2023 09:53

You need what is called a cable thumper, you local power network company should be able to come out and do this, it will cost but you you know exactly where to dig to find the fault and it can then be repaired.

Rust

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#3144229 8-Oct-2023 10:22

rscole86: Could you use a cable locator?

https://www.kennardshire.co.nz/for-hire/test-measure/electrical/pipe-cable-locator-advanced

I used one of these recently to map out a power cable from one building to another (Rural though, across a paddock with lots of trees). It worked surprisingly well.

gregmcc

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#3144236 8-Oct-2023 10:33

Rust:

rscole86: Could you use a cable locator?

https://www.kennardshire.co.nz/for-hire/test-measure/electrical/pipe-cable-locator-advanced

I used one of these recently to map out a power cable from one building to another (Rural though, across a paddock with lots of trees). It worked surprisingly well.

It may show where the cable is.....but not where the fault in the cable is.

some of these machine also need power on the cable and a load on the cable (it detects the 50hz magnetic field).

RunningMan

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#3144239 8-Oct-2023 10:47

gregmcc: It may show where the cable is.....but not where the fault in the cable is.

linw: They know roughly where in the cable the problem is but an electrician dug a couple of holes but couldn't find it.

Sounds like where the fault is is already known, just trying to locate the cable path.

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linw

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#3144253 8-Oct-2023 11:49

Thanks very much your replies. I will point these to my son.

@greggmcc The power company must have used the thumper as they told my son they heard popping.

More background:- there were three houses on the pole fuse and one house blew the fuse. Two of them got reconnected but they found my son's line failed their test.

My son has just hired a generator and he has a gas stove so that will tide them over till his cable gets repaired.

Thanks, again.

larknz

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#3144256 8-Oct-2023 12:00

A good cable location company will be able to tell you pretty well exactly where the cable runs and if they use ground penetrating radar also the depth. If the power company can tell where they heard the thumper you will be able dig the cable up and repair it. This should be much cheaper than a new cable.

PolicyGuy

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#3144278 8-Oct-2023 13:42

linw:

He was quoted $16,000 to put a new cable in!!

Unless it's a pretty old cable, that should be an insurable loss, I'd guess.

Does he have house and contents insurance? If so, it may be time to have a chat with the insurance company

linw

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#3144345 8-Oct-2023 15:43

It's a pretty old cable so no insurance.

linw

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#3144347 8-Oct-2023 15:45

@larknz He has been given the name of an electrician who deals with this stuff so fingers crossed.

This happening over a weekend isn't good timing!

larknz

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#3144349 8-Oct-2023 15:55

Low voltage underground cables don't normally fail. Failure is normally a result of damage to the sheath, either during installation or at a later date by someone installing something like fence post. I would look near any fences or other locations where deep excavation has happened.

everettpsycho

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#3144357 8-Oct-2023 17:36

There's a chance your power distributor will have the plans of where the cable was installed and potentially updated in their GIS system. Some utilities keep better records than others when it comes to on property cables but it's worth asking or doing a before U dig request to see what gets sent back.

SomeoneSomewhere

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#3144381 8-Oct-2023 20:40

Private cables on private properties are usually not recorded in GIS. However, you're likely to find that it's either a) in a dead straight line, or b) in a trench with the water/sewer.

It's odd that the people operating the thumper weren't able to mark it accurately. Usually those are more-or-less as good as any other cable detector, with the benefit that they tell you where the fault is, not just the cable.

If they've given you a rough location of the fault, expanding the hole is probably not a terrible option.

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