Fault on underground Sub Mains cable

[Paul.M]

Had the same fault as above but on a smaller scale (only 30m-35m run).

BS88 L1 blowing taking out a third of a small office block. No obvious reason why until I looked at the newly laid cable run. It was across the entrance of a private car park and the entrance was being used for access to a new building site next door. An empty excavation truck went over the new tarmac and nothing happened. 5 minuets later a loaded truck drove over it and BANG!

Dug up the trench and they may have well used sharpen granite for back fill! It had a "dusting" of sand and the rest was just big chunks of rock. Narrow down your search, hire one of the testers above and check wherever a road goes over the cable run.

 

[Pete999]

Averaging 18inches

https://library.ukpowernetworks.co....ation+of+Underground+Cables+-+LV+to+132kV.pdf

 

[Pete999]

Averaging 18inches

Any sand bed under and over the cable, or cable tiles covering the cable, or has it just been chucked in Willy Nilly and back filled with whatever spoil was left from digging the trench?

 

[kibble19]

Any sand bed under and over the cable, or cable tiles covering the cable, or has it just been chucked in Willy Nilly and back filled with whatever spoil was left from digging the trench?

I know sand bed under and over of 100mm I was there for that, as I know they wouldn't if I didn't make that clear. Back filled with excavated spoil, I understand

 

[Pete999]

I know sand bed under and over of 100mm I was there for that, as I know they wouldn't if I didn't make that clear. Back filled with excavated spoil, I understand

As already mentioned then possible high traffic area might be the site of the fault, you could hire those testers I posted info on, but it's a specialist operation, best bet maybe would be to get a cable tracing company in, the one I used way back was THOMAS CLARKE, don't know if they are still in existence, but a quick google search would come up with option. Good Luck.

 

[static zap]

....... check wherever a road goes over the cable run.

or a emergency passing place ..if single track !

 

[ruston]

or a emergency passing place ..if single track ![/QUOTE

Even a tele handler at 18 inches in a narrow trench will devestate a cable with only four inches of sand over it and backfilled with quarry waste.

 

[Lucien Nunes]

If you can access it you can trace it. However if there are areas that are difficult to access, but you know the route accurately, you could TDR it to find out how far away the fault is from 0ne end. With a reasonable fix from that, a likely cause such as recent groundworks may present itself near the expected fault position.

 

[kibble19]

If you can access it you can trace it. However if there are areas that are difficult to access, but you know the route accurately, you could TDR it to find out how far away the fault is from 0ne end. With a reasonable fix from that, a likely cause such as recent groundworks may present itself near the expected fault position.

Sorry whats TDR?

 

[westward10]

Sorry whats TDR?

Time - Domain Reflectometer.

 

[kibble19]

Time - Domain Reflectometer.

Thanks

 

[Squid]

Back filled with excavated spoil, I understand

So not sure or guaranteed, what was the spec for the job to be done as if someone has screwed up then its their problem and cost to rectify and to reimburse you for your time and expenses.

 

[multimick]

So not sure or guaranteed, what was the spec for the job to be done as if someone has screwed up then its their problem and cost to rectify and to reimburse you for your time and expenses.

only happen again imho.if it is not all dug up

 

[Pete999]

only happen again imho.if it is not all dug up

And done properly

 

[Leesparkykent]

Whetstone bridge theory and performing a Murray loop test if you have a couple of good cores or core and armour.

 

[Pete999]

Whetstone bridge theory and performing a Murray loop test if you have a couple of good cores or core and armour.

https://www.google.co.uk/search?q=w...x-b&gfe_rd=cr&dcr=0&ei=H1vBWd3zLsrU8gfdl4LoBA

 

[Rocboni]

120mm direct in ground seems a bit small for 300amps let alone the 530M run?

 

[Wilko]

Seems to be 223A for ref D and half that for Vd - unless I've missed something?

 

[Rocboni]

Rough calc volt drop would be about 20v for 120mm For that length at 300amp using x value

 

[Wilko]

Thinking ...