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Tracing an underground cable fault?

alanblaby
Has anyone any experience of tracing an underground cable fault?

The cable supplies a private estates street lighting.

It's a 3 core 4mm SWA, approx. 50 metres in length, it has a Line to Earth fault.

I haven't separated the armour and internal earth core, so it could be a armour to Line cable fault, or a CPC to LIne fault. Either way the cable needs to be repaired.

We do not have drawings of where it runs, and from a site survey, it isnt obvious how it has been run either, logic would suggest it runs under the pavement, but a test digging yesterday at the first lamppost suggests it runs a direct route to its source across a garden.

I tested at both ends yesterday, it gave a wandering ~1600 ohms L-E reading, I was hoping the reading would be steady, then I could estimate where the fault was with the differing resisitance values from each end, but the reading was not steady at all - water ingress?

I did zap it a few times at 1000V insulation test, this made no difference, and, of course, gave a 0.00 Mohm reading.


Are there Companies with the equipment that is capable of tracing these faults?

We really don't want to dig up 50 metres of tarmaced pavement.
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  • 0
    An initial question, do you have any good cores not involved in the fault?


    Yes, at least one, possibly 2, though that may not help, as the Boss doesnt want it left as is, as there is clearly a

    fault in the cable, and he doesnt want to leave it with that fault.

    The thinking is, if it is a core to core fault, then we use the armour as CPC, however, if 2 cores are damaged, the 3rd may be on the way out too.

    If it is a armour to core fault, then just use that core as CPC, but, there will obviously be a break in the outer sleeve, and he doesnt want it to corrode any more, which it obviously will.

    Thanks.
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  • 0
    An initial question, do you have any good cores not involved in the fault?


    Yes, at least one, possibly 2, though that may not help, as the Boss doesnt want it left as is, as there is clearly a

    fault in the cable, and he doesnt want to leave it with that fault.

    The thinking is, if it is a core to core fault, then we use the armour as CPC, however, if 2 cores are damaged, the 3rd may be on the way out too.

    If it is a armour to core fault, then just use that core as CPC, but, there will obviously be a break in the outer sleeve, and he doesnt want it to corrode any more, which it obviously will.

    Thanks.
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