Looped supply - power went off when DNO changed the meter next door.

[martygturner]

DNO changed out the meter at my neighbours house, pulled main cut out and bing off went our power for 10 seconds. I was under the impression that the DNO fuse came after the loop join ie on the load side to the meter but seems not. Our meter went dark and stayed off for the hour or so he took to install the new meter.

Our inverter and house carried on chugging after a brief burst of relay activity, however the smart meter went off. So all I can assume is that the live was cut by the fuse pull and the inverter carried on seeing the neutral as connected and just acted like there was no grid import. We tested that at the time by isolating the grid supply and the inverter went off, with the grid connected but no live the inverter was happy enough to power the house.

So in this instance the bit of cable between our houses was still live with power from the inverter back feeding it.

So the question really is that safe, I would assume that the dno treats all incoming cables from the grid as live, however on a looped supply would the expect the loop to go dead after the feed cutout was removed ?

DNO meter chap seemed pretty oh well so what apart from not knowing there was a looped supply seems the map was not right.

 

[ericmark]

So the question really is that safe

No, but as to the rest, not sure, maybe the supply was being unlooped? But your inverter should have shut down if not supply, if there was no supply, how long does it take a smart meter to re-boot, I don't know.

 

[Murdochcat]

May be ask your neighbour if you can look at their service head, seems odd that pulling their fuse would affect your home

 

[martygturner]

Seen the service head looped supply, live was off during the fuse pull. As the neutral is bonded at the service head and the cpc is connected to to the supply sheath there is a earth stake along the looped supply cable or by the very fact that the lead sheath is in the earth.As the inverter requires a neutral earth bond to work in grid / off grid its seen that from the functioning neutral with its earth bond and just carried on.

Spoke to dno - seems that as the loop runs under both houses there will be a fuse in the early 50's head that protects the cable both from the start and another one at my service head, ie a 60amp fuse in my neighbours house. So when my neighbours house has its fuse pulled my electricity will go off, Asked if they were concerned about backflow in this arrangement and they said no, if they wanted to disconnect for maintenance then they would disconnect both L/N at the transformer as this would cause grid tied inverters to shut down Also all supply cable maintenance is treated as live maintenance at all times and as they also pointed out even with my neighbours cut out pulled the incoming side will be live in the head.

So basically perfectly safe.

 

[ericmark]

Thank you for your reply, it was not what I expected, I would hope @flameport would find this thread and comment.

I know my own inverter has a load of little switches that set it to each country's requirements, and even G98 and G99 in this country are different.

I was under the impression that it needed to see voltage between minium and maximum 216.2 and 253, but it does seem there were some changes, so they don't just switch off, but gradually reduce output as the limits are reached, the problem which has been identified is called islanding, where a number of solar arrays see each other as the grid supply, so don't switch off. I was unaware a single inverter could (except for the EPS output) do this.

 

[martygturner]

Well that was an phone call... seems that the advice given was not so much wrong as right and wrong. DNO called yesterday evening. Seems there is an isolation fault that they will fix and will unloop our supply. It seems that from my neighbours supply head there is a fair chance that my inverter was seeing the grid frequency but no amps due to the fuse being out. When these were installed this type has a very close proximity of connections so as they put it with degradation of the head due to age leads to isolation of the loop getting weaker. So whilst no/ little current was passed the degraded connections this still allows for induction/ direct between the incoming supply and the loop. Hence my inverter could see the grid frequency which it relies on and carried on trucking. The did'nt suggest it was something terrible as they will do it as a part of a general unlooping in the next 12 -18 months, they have been having problems with ev charger installs and g99 installs, authorising them then discovering that houses they did'nt expect or knew to be looped were.

In fairness when my house was built in 1949 inverters for homes where unheard off, record keeping was hmmmm. to be fair you would expect terraced/ semi's to be looped but not detached, seems the builders just got it in the post war boom, house a has power but house b does not - I know....

Still say its safe,

 

[ericmark]

My son had something similar, old council house, been sold off for years, and he wanted to swap which room was a kitchen, and rewire the house, and it would suit to get wires off outside of house, so got and excepted a quote to move supply, which would end up making the DNO cable shorter and allowing it to use an outside meter box, so money paid, and rewire cables taken to new consumer unit location, and a temporary cable run from old location to new, until all completed.

He was not actually in a hurry, lack of funds, so it took around a year to 18 months for them to get around to the move. But on arrival found it was a looped supply, and next door had died, a new owner has laid a new drive, where the cables should have run, and an extension was half built where the looped cables ran, so to move his supply easy, but it left next door without a supply, and it seems no way leave in place for the cables between the properties they did not run that way on the plans, so job further delayed, then Colvid so he moved into my house, then he bought my house and had a tenant all which slowed things up more and more. I assume all done now, but don't know.

However it does seem DNO records are often wrong.

 

[ebee]

Yes it is not as uncommon as you might hope, with all of the services.
Where I live a lot of the housing stockis sandstone terrace house built about 1910 mostly but a good measure over the years of other uildings of newer ages.
The local council at the time used to supply the electrics before it became the Boards, records were usually quite decents but there again some assumptions were made.
I particularly remember a stop tap leak in the road and have to be dug up deep down for repairs, working on their charrts they isolated three stop cocks to isolate the one they wanted to work on, no joy . So consulting charts and considering how those assumption errors of yesteryear was a time consuming job and re-evaluating assumptions with more assumptions then tried again and they eventually got it "right" , that took a few days just to do that unseen extra works, and but diagrams in to help the updating of the original charts (hopefuly).
I`m sure similar things could happen with gas and electrics.

A bit like us sometimes when we breakdown a circuit to try to establish where the problem(s) might lay.

Once something gets added or ammended several times over the years it can sometimes bear no relationship with any apparent logical progression unless you happen to discover the timelines and goals at each step which could be a few years apart.