Supply Cable No Earth

[JohnW2]

This is why I think he is describing it as "no approved earth connection"....because there is one, but it is not to standard, possibly because of an earth clamp. The pictures will tell, anyway.

That's obviously what we all initially assume but, as I said, I've started to wonder, both because of the strange wording ("no approved...") and because what he wrote is, in several respects, not what I would expect him to have written if he were talking about a high impedance (connected) TN-S earth.

Pictures will hopefully help us - provided the guy did not change things. Keeping the sheath as an earth and adding RCD(s) (flameport's first and preferred option) is not even mentioned in the note (which talks of only TT and TN-C-S), even though it seems that the guy mentioned (presumably verbally) "an RCD" to the OP. It's all rather odd.

Kind Regards, John

 

[John D v2.0]

Yes he's right it's a dangerous situation, on its own it could cause all the main metalwork in the house to become live assuming the bonding is good. That means you can't get a shock as there is no earth to get a shock from.
However if there is a problem with the bonding too, you might have an earth accessible and get a shock. Definitely get it sorted asap.i agree with the other posters that there's a good chance the dno should provide it for free, but you should still get an electrician to confirm it is safe.
This is an example of an installation with a double fault, with a faulty appliance connected. You have a single fault that we know of so far. http://www.dailymail.co.uk/news/art...cuted-live-tap-ran-bath-familys-new-home.html

 

[Lectrician]

on its own it could cause all the main metalwork in the house to become live assuming the bonding is good. That means you can't get a shock as there is no earth to get a shock from.

Main protective bonding is there to bring everything to the same potential for the short duration of a fault, not to bring the whole place live due to a lack of earth and a fault to earth. That is not desirable.

 

[JohnW2]

... Definitely get it sorted asap.i agree with the other posters that there's a good chance the dno should provide it for free, but you should still get an electrician to confirm it is safe.

Even if the 6.65 TN-S earth is connected, I would not regard it as particularly 'safe' in the absence of RCD protection, even though you are theoretically right in saying that it should not present a threat to life if the building really is an equipotential zone. Although the VD in the CPC of a circuit with an L-E fault means that there will be a pd between exposed-c-ps on that circuit and the exposed-c-ps of other circuits, with such a high Zs, the VD, hence that possible pd, would presumably not be high enough to present a major hazard.

I suppose it could just be a quirk of the guy's use of language, but I still find what he wrote to be odd if what he was saying that there was a connected TN-S earth with too high a Ze. If I tested, say, an RCD (particularly in a TT installation) and got unsatisfactory results, I would report that the RCD was faulty, or that the test results were unsatisfactory, or something like that - and I wouldn't dream of reporting the situation as "there is no approved RCD in the installation", would you?!

Kind Regards, John

 

[EFLImpudence]

What I don't understand is -

The form/inspector is from UKPN - the DNO.

If the sheath is supposed to the the installation earth and he has found it to be unsatisfactory, why is HE not arranging the improvement but stating that an 'electrician' should be contacted for the possible connection of PME?


According to other threads and places, UKPN do not seem to be the best DNO in the country, but even so...

 

[JohnW2]

What I don't understand is - The form/inspector is from UKPN - the DNO. If the sheath is supposed to the the installation earth and he has found it to be unsatisfactory, why is HE not arranging the improvement ...

Exactly - which is why I have come to wonder whether the DNO has ever supplied an earth. If it has (indeed, if that TN-S earth is still connected to the MET), then the guy doesn't seem to undertsnad his employer's obligations under ESQCR.

.... but stating that an 'electrician' should be contacted for the possible connection of PME?

He didn't quite write that. He said to get an electrician to install a TT rod OR to get UKPN to "install a PME system" (at the customer's cost).

None of it makes complete sense to me.

Kind Regards, John

 

[EFLImpudence]

He didn't quite write that. He said to get an electrician to install a TT rod OR to get UKPN to "install a PME system" (at the customer's cost).

That's true but it won't be a decision for an electrician to make so why didn't HE ask the customer which was wanted.

None of it makes complete sense to me.

Also true but it was UKPN who wrote it.

 

[JohnW2]

That's true but it won't be a decision for an electrician to make so why didn't HE ask the customer which was wanted.

Don't ask me - either you, a crystal ball or UKPN will have to give the answer to that!

I suppose that the simplest answer would be that the UKPN guy simply didn't know what he was doing or talking/writing about, and didn't even have any common sense!

Kind Regards, John

 

[John D v2.0]

it's a dangerous situation

That is not desirable.

"not desirable" is an understatement - I still consider it dangerous as any issue with the bonding or the edges of the zone could be lethal (for a long period of time)

dno should provide it for free, but you should still get an electrician to confirm it is safe

Even if the 6.65 TN-S earth is connected, I would not regard it as particularly 'safe' in the absence of RCD protection

When I said provide an earth, I didn't mean connecting a broken one, I meant a compliant one. The electrician when confirming it's safe should confirm that it's really low enough, and connected properly within the customer's installation. I've heard stories of DNOs providing an earth terminal and not connecting it to the existing MET, stating that it's not their job to touch the consumer's installation.

 

[JohnW2]

When I said provide an earth, I didn't mean connecting a broken one, I meant a compliant one.

I realise that but, despite what he wrote, the DNO guy appears to have suggested that the OP could 'go with what he's got' (and add an RCD) ("He indicated that the best course of action was to install a RCD"), which is much the same as flameport's preferred option; I take his point that, if one regards it as a 'TT electrode' (and adds RCDs), it is currently much 'better' than any domestic rod is likely to be, but it doesn't sound like a very good long-term solution, since one doesn't know how quicjkly, or to what extent, it may 'deteriorate'.

The electrician when confirming it's safe should confirm that it's really low enough, and connected properly within the customer's installation.

I'm not sure what you're talking about there. We know that the incoming cable sheath is not, evn now, low enough in impedance to be used as a TN-S earth (although, as above, some people might regard it as a 'TT electrode') - and if the DNO provided a TN-C-S earth, one assumes that it would more-or-less inevitably have a low enough impedance.

Kind Regards, John

 

[John D v2.0]

I'm not sure what you're talking about there

Maybe I wasn't clear enough as it's pretty simple conceptually, it's a basic test, if it's TNCS or not an electrician would still test it. And it won't be any use if it's sitting there all alone on the meter board, so that would be another obvious thing for the electrician to confirm, that it's actually connected to the CPCs in the CU and the main bonding.

 

[JohnW2]

Maybe I wasn't clear enough as it's pretty simple conceptually, it's a basic test, if it's TNCS or not an electrician would still test it. And it won't be any use if it's sitting there all alone on the meter board, so that would be another obvious thing for the electrician to confirm, that it's actually connected to the CPCs in the CU and the main bonding.

The one thing which I think we are all agreed on, is that something needs to be done, ASAP.

If we can trust anything which this DNO guy said/wrote, we presumably have to assume that there is currently neither a TT or TN-C-S earth, and that at least some of the circuits are not RCD protected. We also know that, even if the cable sheath is connected to the MET and CPCs, it is too high in impedance to be acceptable as a TN-S earth. Taking all that together, I think that we know what an electrician's testing would reveal - namely that some (or all) of the circuits do not have adequate protection (i.e. neither OPD-mediated ADS or RCD protection), and are therefore 'not safe'.

As the DNO person suggested, an electrician could make the installation temporarily reasonably safe by installing an up-front RCD but, ironically, unless there is an isolator, that would theoretically require the DNO to attend (twice) to pull and reconnect the cutout fuse (in which case they probably could do what they probably should be doing ).

Kind Regards, John

 

[securespark]

OP: who took the picture of the form?

 

[chivers67]

If the sheath has already got up to nearly 7Ω, is it not probable that it will progressively deteriorate to the point that one of the other options will then have to be adopted?Kind Regards, John

I hadn't considered using the sheath like that especially as you don't know the length but as you say below 7Ω , cheers.

What do people consider the best method of connecting the earth to the other sheath without damaging it though? (I've only seen lead cable inside properties serving lights or sockets previously).

 

[Blueflash]

I would strongly advise you leave well alone and pay to have a PME supply installed.

Dave