Appliances in single phase property damaged by 415v

[Simon47]

The ground mat isn't just about grounding, it's also about creating a safe environment for people. So even if they put 'kin big earth rods in, they'd still need the ground mat covering the whole substation site to avoid any possibility of dangerous potential differences from being present.
And even if you could rule that out, you'd need some large bonding cables - which would also be a target.
At least the earthing mat is buried which makes it less trivial to steal than above ground cable.

Unfortunately, the nature of the electricity distribution system is such that it's inherently difficult to secure - a lot like railway infrastructure. I was a talk a few years ago where it was mentioned that in some places they bury cable ducts under the middle of the track bed (i.e. under the sleepers), and a whole meter down to try and reduce cable thefts.

I've also seen adverts (aimed at large users like railways operators) for cables with the customer name embedded within the cable - as in, a small tape, with the name punched in it, embedded in the copper strand layup. Short of chopping the cable into tiny fragments, or melting it, it's impossible to destroy the evidence, and thus make it traceable when it turns up in a scrapyard where it shouldn't be.

 

[JD6400]

In fairness to the op , even if he had looked deeper into the fault what more could he have done !?
If they are not coming out , that is what you are getting .
Admittedly for those of us that have dealt with these , jobs worth ----ers on the end of a so called utilities help line , we would have a new somewhat larger ring piece ripped.in no time at all .

And to honest , out of the 8 or 9 times that I have come across lost neutrals , it has never shown 415v present between either phases or neutral.
The only time I have seen 415v was at the beginning of the year on a completely new build farm . They had just moved in about a week before hand , and one Sunday night the neutral on load side of the new TX failed and as it burnt out it curled over and made connection with L2 .
Luckily it only seemed to obliterate the house , but that came to just over £60k. ?
The first I found out about it was a call at 6:30am on Monday morning , as we had installed 12KW of solar on the grain store when we wired the shed up, and the spark appointed by the DNO , who had been there doing an EICR and cataloguing the damage from 11:15 pm on Sunday night !!!! Was not sure about the 3ph pedestal grain fans and the solar.

 

[Lister1987]

After a quick read of that it looks like the fault in this thread is not reportable

If it didn't fall under ESQCR, you could try RIDDOR, even if it doesn't qualify there either, it's putting pressure on the DNO. It would be interesting to see HSE actually get involved in cases like this but they seem all too happy leaving it to the DNOs to deal with, brush under the carpet, not maintain thier system and give bonuses to the fat cats for a 'good job' managing the networks

 

[I Trippet]

As said, knowing the basics of the distribution systems in use and the fault symptoms is useful even though they are out of your control.
That you measured 415V suggests a loss of neutral in the supply network. Turn to page 48 of the Wiring regs and look and figures 3.8 and 3.9 - from the sound of things, 3.8 for TN-S. Doodle in a star transformer for the supply - the local substation. Now consider what happens if the neutral cable between substation of consumer gets cut/broken. You now have a floating neutral, and the individual phase-neutral voltages for each phase will depend on the relative loadings.
In the traditional depiction of a star transformer, the arrangement of the windings corresponds with the phase diagram for the three phases. Once you lose the neutral, then the common point as seen by the loads will not be in the middle of the star.

In the best case, the loads are all the same, the phases are balanced, and there will be little difference to normal. But that's rare. Worst case is that one phase is heavily loaded, while the others are only lightly loaded. In this case, the phase-neutral voltage of the heavily loaded phase will be reduced, and those of the other phases will be increased - the neutral will drift until the currents are balanced.

Of course, as bulbs blow, fuses/breakers trip, and things generally let the magic smoke out - the loads on the phases showing higher voltages will reduce, and the imbalance will get worse. In extreme, you could end up with nothing on two phases, and a large resistive load on one phase - so one phase now gets very little because the neutral point is now pulled out to that corner of the phase diagram, while the other two phases now get 415V P-N (the neutral is now effectively one of the other phases).

Unfortunately, the <insert you own expletives here> who nick metal don't care about what damage they cause. So stealing a neutral earthing link for a substation might get them a tenner in scrap value, but cause many thousands in damage. The DNOs tend to hush up the problem, especially if someone is clever enough to get themselves injured or killed - the HSE people tend to take the attitude that the DNO should have done more to protect the sort of people who break into a locked compound, with security fencing, and with plenty of "DANGER OF DEATH" signs - and then interfere with what is obviously live electrical equipment ?

That's pretty much what I said, but for whatever reason that made it clear that I "lack some very basic knowledge of the electricity distribution system", which is actually completely wrong.

Anyway, I've spoken to the lady again, she's been in contact with Northern Powergrid and they have confirmed their engineer didn't do any investigative work, just came to the apartment, checked the supply voltage, said it was fine and left. They apparently don't seem to think there is any fault, despite me explaining to them 3 times - first in the early hours when it happened, and twice the next day (had to call back because she was out at first and they wanted confirmation she would be there) - that I was getting 415v when I was called out. So how they can be satisfied that there isn't a fault and that it won't reoccur is beyond me.

 

[marcuswareham]

That's pretty much what I said, but for whatever reason that made it clear that I "lack some very basic knowledge of the electricity distribution system", which is actually completely wrong.

Anyway, I've spoken to the lady again, she's been in contact with Northern Powergrid and they have confirmed their engineer didn't do any investigative work, just came to the apartment, checked the supply voltage, said it was fine and left. They apparently don't seem to think there is any fault, despite me explaining to them 3 times - first in the early hours when it happened, and twice the next day (had to call back because she was out at first and they wanted confirmation she would be there) - that I was getting 415v when I was called out. So how they can be satisfied that there isn't a fault and that it won't reoccur is beyond me.

It would appear as if the DNOs have little regard for high impedance / open neutral faults, scary !

 

[Sparkgap]

It would appear as if the DNOs have little regard for high impedance / open neutral faults, scary !

Not only those faults: I have a substation halfway down my garden which supplies most of my road via overhead lines. We've had two faults of interest: first was a failure of the HV connection onto the transformer which required chopping the incoming HV cable and reterminating it. While this was being done over a couple of days we were hooked onto a supply from a transformer in the next road over. As a result my house voltage (normally 245V) varied from 230V down as low as 178V. I did phone the DNO to check on progress as I was a bit concerned at the low voltage possibly damaging equipment in my house but the guy on the phone said there was nothing they could do (which is more than likely). Fortunately I had no issues and the fault was sorted relatively quickly.
The second fault was loss of one of the HV phases feeding the substation which resulted in my supply dropping to about 88V. This was due to tree branches striking the overhead wire (according to the DNO engineer I talked to when he came to check the line they had cut back on cutting back(!) nearby trees generally and this could be a problem in future with strong winds). One surprising thing was some of my lights still worked: normal GLS tungsten bulbs gave a dull glow, most of my LED lamps didn't work but a couple of LED lamps plus the DAB radio in the kitchen all worked perfectly! I assume these were all switch mode psu and able to cope with the low voltage.