Builder needing advice after damaging temporary supply to new build!

[shaun rosier]

Hi Everyone,

I would really appreciate some advice on the following problem I have had with a temporary electric supply.

We are in the process of building a couple of flats and had a temporary supply put in, no problem! However much later when one of the labourers was putting the hockey sticks into the new boxes and needed to bust through some of the footing he stupidly damaged the cable with a breaker and grazed the cable exposing the outer sheath (cable was not severed) and there was a load bang and the cable started fizzing in the hole which was filled happened to be filled with water!

We called the supplier out to repair and two guys turned up to repair the cable and one of them got a zap of the cable as he tried to repair it. Before this the same labourer got a zap off the site cabin handle after he went through the cable.

We then had the two neighbours that lived down the lane come out and say there TVs had blown up!

The engineer said that there was no way that us going through the cable would have caused the TVs to blow and it was just a coincidence! I just don't believe that as it happened at exactly the same time!

He then called his boss and about 5 vans pulled up within about 20mins and started to take down the over head cables to the main road. They replaced a stretch of the cable and were working on one of the poles.

I don't remember exactly what our sparky said but he thinks that the supply cable had an existing fault and that the sheathing was somehow live and that's what caused the cabin to become live when it was damaged and the cable was possibly 'vibrating' and caused a surge down the line to blow up the TV's. This he says may be why the engineer got a shock as he didn't expect the sheathing to be live!

The reason why I could really do with some advise on this one is because the supplier is charging me for the whole team that turned up (about 6 guys) for about 5 hours with the overhead work when I was just expecting to pay for the two guys for a couple of hours to fix my temporary supply not half the road! I have offered to pay them what I think is fair but they say they will bring me to court if I don't cough up in full!

Any advice would be most welcome from the pros!

cheers

Shaun

 

[Squid]

Explain please

 

[Lucien Nunes]

Ignore eddy currents, C/T-E site trannies etc, all irrelevant. If the overhead cable affected was the LV 400/230V supply to the property, I read the scenario as follows:
1. There was an existing defect on the DNO's CNE conductor or connection to it. Not your property, not your fault.
2. The builder caused an L-E or L-N fault on the service cable to your property. In the time it took for the OPD to clear it, the existing defective CNE / neutral connection or cable went open-circuit.
3. This left some consumers on a 3-phase distributor sharing a disconnected neutral, leading to incorrect L-N voltages. Some of them received more than 230V, blowing up their TVs.
4. Your site was also left with an open CNE resulting in tingles / shocks to anyone touching it outside the equipotential zone.
5. The DNO's team had to repair the distributor first, as this was preventing them supplying other customers.

Actually, was it the service cable (before the meter) or your submain (after meter) that was hit?

 

[johnduffell]

I don't understand the talk of PME - how on earth does the equipotential zone work on a construction site? The only way to ensure safety would be to use a local earth for all CPCs otherwise you risk introducing other potentials through the supplier provided protective connection.

 

[Midwest]

Guess the supply cable would be PME (i.e. the one damaged), the building site temporary's connected to TT, unless all extraneous conductive parts are connected to the MET.

 

[ruston]

@Midwest . Yes it depends how diligent they have been with the temporary supply. Nothing goes wrong until it does.

 

[westward10]

And nothing is impossible given the correct circumstances.

 

[Lucien Nunes]

Of course where I wrote CNE conductor above, it might be a PEN, but as it caused such far reaching effects it seems not to have lots of decent ground paths shunting it.

 

[westward10]

Of course where I wrote CNE conductor above, it might be a PEN, but as it caused such far reaching effects it seems not to have lots of decent ground paths shunting it.

Your scenario seems highly likely. The OP really needs a technical report stating the cause and effect of what occurred then I suspect the charges maybe reassessed.

 

[Lucien Nunes]

The only way to ensure safety would be to use a local earth for all CPCs

Yes the site temp was presumably on TT, but if the service cable was connected to a PME system, an L-CNE fault current could have blown a defective PEN O/C elsewhere, where other properties were relying on it.

E2A Ah I see your point, the site should not have had stray voltages on its CPCs / bonding due to the failure if it was TT, although we don't know what was shorted to what at the fault location so it's difficult to predict. If the floating section had come into good contact with true earth, and we know the hole was full of water, there could have been all sorts of voltage gradients about the site.

 

[Wilko]

Hi - apologies if this has already been said or is rubbish (please correct me) - if the DNO cable was concentric, then our man has exposed the N by nicking the cable. The N would have to already have been well above a few volts to cause the bubbly water that's reported. So either more than a nick or distribution system already in trouble, or both (?). A pic of the damaged cable might be interesting .

 

[elsparko]

That's exactly what I thought Richard, sounds like they are trying to blame me for a fault in there network! The engineer got a shock when he touched the outer sheathing wires as he took his gloves off, he obviously wasn't expecting them to be live!

but the cable was damaged, he should have at least tested the sheath

the only time i willingly touch conductors is when i know 100% that they are dead.

 

[elsparko]

Hi - apologies if this has already been said or is rubbish (please correct me) - if the DNO cable was concentric, then our man has exposed the N by nicking the cable. The N would have to already have been well above a few volts to cause the bubbly water that's reported. So either more than a nick or distribution system already in trouble, or both (?). A pic of the damaged cable might be interesting .

i was on a large steading job, diggers outside working on the underground heating system, then a loud bang and some smoke coming from their ditch

hydro boys came out and sorted it and everything was back to normal, so i sense that the suppliers network is not up to standard in this particular case

still, the labourer caused the fault(straw) that broke the camels back

if i had any inclination there may be a live cable buried, id use a trowel with an insulated handle!

anyone ever seen the video of "travellers" stealing railway lines? using axes to cut the cables...

 

[Lucien Nunes]

(please correct me) - if the DNO cable was concentric, then our man has exposed the N by nicking the cable. The N would have to already have been well above a few volts to cause the bubbly water that's reported. So either more than a nick

Much more than a nick... OP says there was a loud bang so he almost certainly shorted L - PEN within the cable, and it was that fault current that broke the continuity upstream.

 

[elsparko]

any pictures of the bit that hit the live cable? how much of the steel is missing?

 

[stevels4]

DNO will only install a temporary supply using TT, they insist on having the Earth Rod in place or they won’t connect meters.

DNO’s do not connect meters, they will run the service cable to a cut out which may also be TNCS, MOPs supply and fit the meters.