Electrics after a fire

[MickieMonday]

When my parents were away, they had a fire about the size of a large dining room table. It seems that the rubber carpet tiles had smoldered and burned through the wooden floor, which collapsed into the 18 in void below. The loss adjuster said he has never seen a fire like that go out by itself.

Anyway, the fuse box is on the other side of the wall and all the wires running under the floor inside metal conduits were rendered useless. It is an old house and many of the sockets still have cloth insulation. Not only that, the whole house is wired with a shared neutral and earth. I understand that this was not uncommon back in the day and that neutral is earth at the substation.

The insurance companies schedule of work is pricing up the installation of a new consumer unit and reconnection to the existing wiring system. My question is whether an electrician would be willing to do this. It has been worrying me because they are pensioners and we don't have the ready cash for a rewiring job at the moment.

Thanks for your advice,

 

[Murdochcat]

The first step is to get a decent EICR to establish the scope of the damage and also the state of the existing installation across the whole property

Fitting an up to date fuseboard to such s property could open a nasty can of worms

 

[flameport]

, the whole house is wired with a shared neutral and earth. I understand that this was not uncommon back in the day

That was never common, and for domestic properties in the UK is basically unheard of. Some Eastern European countries used such things decades ago.
In the UK some industrial installations were wired that way, but even those will be 60+ years old by now.

neutral is earth at the substation.

That is correct, but is irrelevant.

 

[ericmark]

I do see the problem, cloth insulation is well past its use by date, so does need renewing, but the reason it needs renewing is not because of the fire, but we can continue to use wiring which has been there for years, but we can't add to it, unless it complies with current regulations.

The existing would need testing, and it would seem unlikely that it would pass, it would likely cause the RCD/RCBO to trip, so it is very unlikely one could use the old wiring even if you wanted to.

But as to how you get insurance to pay, for what is fair ware and tare, I don't know.

 

[Jurassicspark]

When my parents were away, they had a fire about the size of a large dining room table. It seems that the rubber carpet tiles had smoldered and burned through the wooden floor, which collapsed into the 18 in void below. The loss adjuster said he has never seen a fire like that go out by itself.

Do you know why and what caused it i.e any symptoms that might have aided the fire? Was the installation loaded in any way?

Anyway, the fuse box is no the other side of the wall and all the wires inside metal conduits rendered useless. It is an old house and many of the sockets still have cloth insulation. Not only that, the whole house is wired with a shared neutral and earth. I understand that this was not uncommon back in the day and that neutral is earth at the substation.

Do you mean that the installation is tncs?

 

[MickieMonday]

I do see the problem, cloth insulation is well past its use by date, so does need renewing, but the reason it needs renewing is not because of the fire, but we can continue to use wiring which has been there for years, but we can't add to it, unless it complies with current regulations.

The existing would need testing, and it would seem unlikely that it would pass, it would likely cause the RCD/RCBO to trip, so it is very unlikely one could use the old wiring even if you wanted to.

But as to how you get insurance to pay, for what is fair ware and tare, I don't know.

You hit the nail on the head. The old wiring would have 'seen them out' as they like to say.

 

[MickieMonday]

Do you mean that the installation is tncs?

I had to google tncs. The explanation was a bit complex. All I really know is that there are only live and neutral behind the socket faceplates. They've never had a problem, so far.

 

[MickieMonday]

That was never common, and for domestic properties in the UK is basically unheard of. Some Eastern European countries used such things decades ago.
In the UK some industrial installations were wired that way, but even those will be 60+ years old by now.



That is correct, but is irrelevant.

I'll take your word for that but I'd be interested to hear why you need the separate earth wire if neutral is earth at the substation? If I had to guess, I wonder if it has something to do with somebody swapping live and neutral at one of the sockets?

 

[EFLImpudence]

I had to google tncs. The explanation was a bit complex. All I really know is that there are only live and neutral behind the socket faceplates.

Then none of the metal exposed-conductive-parts of their appliances (e.g. cooker carcass) will be earthed.
Meaning that if they should become live because of a fault they will stay live instead of the fuse/breaker disconnecting the supply.

They've never had a problem, so far.

That's lucky.

I'll take your word for that but I'd be interested to hear why you need the separate earth wire if neutral is earth at the substation?

Because there is nothing connecting the metal exposed-conductive-parts of their appliances to that earth.

If I had to guess, I wonder if it has something to do with somebody swapping live and neutral at one of the sockets?

Not really but that is another matter.

 

[ericmark]

I would say the question is more why was TN-C-S or the other name PME was ever allowed? The idea is there are multiple earth points, so the protective multiple earth was very unlikely to fail, TN-C-S the C stands for combined and the S separated, so where the cable is so large that it is extremely unlikely for it to fail, however we are seeing the problem with EV charging points, where when it fails it could be fatal, so we are fitting devices to detect the failure which can auto disconnect the supply.

Within the equipotential bonded area, loss of the combined neutral and earth (called the PEN) can result in some dramatic voltage swings, but like the birds on the power cable, since all is bonded together, there is no danger to personal, it may fry equipment, but not people.

It would be interesting as to how far back, in 1966 the rules changed for lights, now only pendent lamps are allowed without an earth, but before 1966 filament lamps (so did not apply to fluorescent lamps) which were not easy to touch at the same time as other earthed items, so did not include wall lamps, were allowed not to have an earth run to them.

But the way lights were changed, it was made a rule even if the lamp was class II (does not need an earth) there still has to be an earth available in case the lamp is changed.

There are a few odd things, like a shaver socket which is an IT supply, (insulated from terrestrial) but when the BS1364 socket (13 amp) came out post-war, the use of two pin outlets stopped.

But in North Wales I have noted council houses were wired using metal conduit, and the conduit was the earth, but it was not threaded like the latter versions, so this was common.

We should use a meter to test the earth and the whole house should be tested every 10 years (5 years for rented) so since 1966 so at least 5 times, someone should have alerted the owners work needed doing.

The regulation book with each edition has a statement on the lines of

Existing installations that have been installed in accordance with earlier editions of the Regulations may not comply with this edition in every respect. This does not necessarily mean that they are unsafe for continued use or require upgrading.

note "not necessarily" which can also of course mean they do need upgrading.

The problem is one where x is now allowed if y is done, and often x is then done without y being done, and sometimes no option, like fitting LED bulbs instead of tungsten. The other is the clarification, where it is realised the regulations have been miss read for years.

Some changes are due to new technology, like microgeneration, but however much I may want to, I can't use tungsten bulbs, and with LED I can get hold of a live bulb, with tungsten I would have burnt my hand if I had tried.

But as to trying to force an insurance company to up-grade the home, that's a problem, in the main the problem is the RCD, today we need to fit them, and it is unlikely the old wiring would allow the RCD to be switched on, so can't see how one could get away without a rewire.

 

[morqthana]

That was never common, and for domestic properties in the UK is basically unheard of. Some Eastern European countries used such things decades ago.
In the UK some industrial installations were wired that way, but even those will be 60+ years old by now.

Wiring done by a moonlighting electrician from a nearby factory, possibly using materials he liberated from the stores?

 

[Jurassicspark]

All I really know is that there are only live and neutral behind the socket faceplates. They've never had a problem, so far.

No apparent shocks from the metal body appliances that leak current to earth during their suppression?

So whoever rewired or wired your home actually cut off the earth wire before installing the sockets?

Or did they wire it with singles or with a cable that doesn't incorporate the earth wire?

Or did you unscrew the socket, which was a spur, added by someone who did not know what he was doing and now you assume its like that for the entire property?

Dangerous situation as said above and it should be rectified as soon as possible.

Instead of lingering around asking questions on this forum you need to get an EICR carried out that should tell you what is going on.

 

[endecotp]

the wires running under the floor inside metal conduits

All I really know is that there are only live and neutral behind the socket faceplates.

They have live and neutral singles inside steel conduit; the steel itself is the earth. This is common, and a perfectly acceptable safe installation method, but apparently often misunderstood. The danger is that someone who doesn't appreciate that the steel is the earth thinks "it's not earthed" and makes modifications that really aren't earthed.

 

[Harry Bloomfield]

They have live and neutral singles inside steel conduit; the steel itself is the earth. This is common, and a perfectly acceptable safe installation method, but apparently often misunderstood. The danger is that someone who doesn't appreciate that the steel is the earth thinks "it's not earthed" and makes modifications that really aren't earthed.

It was grip conduit, and often the joints developed a high resistance, after a while.

 

[endecotp]

It was grip conduit

What has @MickieMonday said that makes you believe that?