Builder needing advice after damaging temporary supply to new build!

[littlespark]

I believe the question is “did the incident on the building site cause the damage to the suppliers cable, or was the damage there before?”

Answering this will ascertain who needs to pay for the repair job and 2 tellys.

Maybe you need to get a professional in. Ie, a lawyer.
Unfortunately questions will be asked about safe working practices, and HSE will get involved.

Hopefully no one was seriously hurt, but left undiscovered, the fault could have been catestrophic.

 

[westward10]

HSE won't get involved.

 

[buzzlightyear]

maybe jack hammer Charlie was left loose ,tight have caused a spike on the cable .the op said the cable was only grazed. but we are not there .but we can only take this word .

 

[Pete999]

Eh ?

Double Eh

 

[Pete999]

Eddy currents?

Explain please

 

[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.

 

[LankyWill]

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.

I am aware of this, it was just a generalisation.

 

[shaun rosier]

Looked at the latest email from the supplier and this is what they said!

"The damaged caused an open circuit neutral fault. Where the cable has been damaged it has caused a surge down the overhead network and we have had to replace the ABC conductor and overhead span to rectify this."

"Had there been a fault on the network already we would have known as we would have received prior call outs."

 

[shaun rosier]

Thanks for all your responses by the way, really appreciate all the advice/info!

 

[elsparko]

Thanks for all your responses by the way, really appreciate all the advice/info!

im surprised how the fault caused 2 t.vs to "blow up"

my dad wanted a new t.v but mum said no, so he poured some water down the back of it that night and we had a flatscreen the next day

if it damaged their network it suggests their network was substandard to begin with

not that i know a great deal about overhead lines so i could be wrong but my logical lizard brain tells me to go with what seems most obvious

 

[westward10]

Looked at the latest email from the supplier and this is what they said!

"The damaged caused an open circuit neutral fault. Where the cable has been damaged it has caused a surge down the overhead network and we have had to replace the ABC conductor and overhead span to rectify this."

"Had there been a fault on the network already we would have known as we would have received prior call outs."

The fault on your cable should have caused no detrimental issue to the supply network.

 

[shaun rosier]

blew up one of their kettles as well apparently!

 

[telectrix]

don't the DNO fit fuses to prevent such damage to their precious network?

 

[elsparko]

blew up one of their kettles as well apparently!

if i was you, id hire a solicitor as it sounds like the 2 neighbours are taking the michael, and so are the supply company.

 

[elsparko]

don't the DNO fit fuses to prevent such damage to their precious network?

yeah but this sounds like it was the cable before the service head

 

[telectrix]

substation has fuses as well.

 

[westward10]

I have said before you need to ask for a technical report.

 

[elsparko]

substation has fuses as well.

if their fuse didnt react then their system design is a failure, so they should be liable for their own overheads, then the labourer responsible for the damaged cable from overhead to temporary

the 2 neighbours banging on about their appliances can as good as be ignored

guarantee if you open up these appliances and have a gander it will tell you all you need to know.

 

[johnduffell]

The dno design their network on the basis that there won't be many faults, none of this fault protection nonsense.
Since they can just claim back any costs of blowing up other things from whoever they blame for a fault.
No idea who wants to claim a kettle, not the best scam to pull, or has Mr Dyson started making fancy expensive kettles?

 

[Richard Burns]

The ESQCR regulations require the generator or distributor to "ensure, as far as reasonably practicable, his network does not become disconnected from earth in the event of any foreseeable fault" and a "distributor shall ensure that a supply neutral is connected with earth at... such other points as may be necessary to prevent, so far as is reasonably practicable, the risk of danger arising from the supply neutral conductor becoming open circuit"
A short circuit on a supply conductor is eminently foreseeable and they have already admitted to having an open circuit neutral.
This does not detract from the dangers of the construction company operations but should limit their responsibility to the area of actual damage and not subsequent failures on the existing network.

 

[alasdairp]

Lucian Nunes posted the best response imho. There was almost certainly an existing distribution network fault on that part of the network. Broken Neutrals, especially on early XLPE 3-core cables when the Neutral and earth are carried by the armour (i.e. the Neutral does not have a 4th internal conductor), are suprisingly common - water gets in the the armouring eventually rusts through. Everything usually continues to work ok because of the use of PME. I have detected many of these faults over the years. One of the worst cases was about 360 amps going back through the building steelwork and various undergound metal pipes to the substation. In another (even worse) case the DNO Electricity had fogotten to reconnected the Neutral in a 1 MW internal substation for a large office and shopping complex - all currents were returning via the protective Earth!!! The only problems reported were "wobbling CRT computer monitor displays" due to the high EMFs caused by the current loops formed.

What I suspect happened in thei builder's case here was that there was an existing broken Neutral in the part of the network supplying his temporary supply and the damage current (the 'bang') went to the 'Earth' connection which also happend to be working as the Neutral to houses also on the same 3-phase LV circuit feed . This will have caused some homes to get a sudden short drop in supply voltage and people on one of the phases (not the one hit by the jack hammer) to get a short high voltage surge - up to maybe 360 volts (or so) - hence the damaged TVs.

The idea of PME was to try to prevent this sort of thing from happening - the downside is that serious Neutral faults can exist which are not detected or corrected. I tried (at a high level) to get the ENA to implement an LV 3-phase cable overall current-balance check whenever they did work on a network - but they said it would add too much cost and bother. It is so simple to do with a large clamp or Rogowski coild meter - so I suspect they really just did not want to detect a load more Neutral connection faults.

I would definitely contest it and ask for a #detailed# report on #all# the work that was required to be done on the LV network and the reasons why. I suspect they are taking the p*** at your expense. The TV people should also be able to claim compensation from the DNO.

 

[Lucien Nunes]

Alasdair's explanation is even more convincing - that it was a PME service that had already lost its neutral upstream and carried on without symptoms. The DNO will have a job arguing that your service cable fault directly caused that problem without at the same time revealing that they were not complying with the ESQCR. Subject to the specifics in the report, I can't see how you could be held responsible for it, or the consequential damage.

FWIW I 've fixed a ton of electronic gear that has been blown up by a wandering neutral. It's a specific hazard in my industry with lots of temporary 3-phase TNS on single-pole connectors and cables. Unlike lightning, which can destroy every semiconductor in one hit, the modest over-voltage of 400V maximum only normally affects the PSU and often just a few components within it. Repair was usually viable and well worth doing, although we sometimes had to write things off for insurance reasons depending on the circumstances. That was professional kit though, where a rack might be worth £100k or more.

 

[elsparko]

Alasdair's explanation is even more convincing - that it was a PME service that had already lost its neutral upstream and carried on without symptoms. The DNO will have a job arguing that your service cable fault directly caused that problem without at the same time revealing that they were not complying with the ESQCR. Subject to the specifics in the report, I can't see how you could be held responsible for it, or the consequential damage.

FWIW I 've fixed a ton of electronic gear that has been blown up by a wandering neutral. It's a specific hazard in my industry with lots of temporary 3-phase TNS on single-pole connectors and cables. Unlike lightning, which can destroy every semiconductor in one hit, the modest over-voltage of 400V maximum only normally affects the PSU and often just a few components within it. Repair was usually viable and well worth doing, although we sometimes had to write things off for insurance reasons depending on the circumstances. That was professional kit though, where a rack might be worth £100k or more.

100k? pop that down to the scrappy at lunchtime and go 50/50 with the boss aye?

maybe worth letting the supply company take you to court, then get a payout in your favour for your time etc.

 

[Toneyz]

It is where the neutral and earth of the consumer's installation is joined together so on the supply side you have the live conductor and the outer armouring in the combined neutral/earth conductor.

Why the dumb Rigpig at least have the decency to correct me or give the other viewpoint.

 

[123]

Why the dumb Rigpig at least have the decency to correct me or give the other viewpoint.

Chances are it's accidental on a phone. I've done it a few times, even when just trying to scroll down the screen

 

[johnduffell]

Chances are it's accidental on a phone. I've done it a few times, even when just trying to scroll down the screen

Yeah every time i post something loads of people accidentally hit disagree or dislike, really annoying