Following up on the recent thread about Earth Resistance measurements

[sophiecentaur]

I have recently moved into a new (rather ancient) house and had a few trips of my Residual Current breaker.

I dug out my old Socket tester which tell me the three pins are correct. But then the Red warning light tells me my socket(s) fail the loop test.
I never had this before but my last house had an overhead supply with no Earth from the company. The tester said "get this checked" and the man said the (high but not ridiculous) earth resistance was acceptable. I stuck a new copper earth spike into the ground with a pair of thick earth conductors connected to my system and it was 'better but my tester was not totally happy.

My new house has an underground supply and all the metal bits in the house seem to be connected by a maze of earth conductors but I can;t find any conductor going to Earth. Previous houses all had underground supplies and a strap round the armoured supply cable so I assumed I would find the same. But no. Also, if I stick my meter pointed probe into the cable cladding, I get many kΩ when I eventually make contact. How bad is that? I feel safe within the house as everything in it seems to agree about zero potential. Would a better earth reduce the likelihood of annoying RCD trips? I thought it might be the problem.

Being a bit lazy I thought that PF could give a quick, if unofficial answer. The house is 1930 build iso it will have had several generations of installations - including an array of 10 PV panels. Is it possible that the PV system could have changed the situation? It seems to be documented.

 

[Baluncore]

I never had this before but my last house had an overhead supply with no Earth from the company.

I guess in the UK you have a MEN system. That will have no PE from the supplier, only a neutral. Does the armoured supply cable contain both Neutral and Active conductors? The armour on the supply cable will be earthed at the supplier's end.

In the distribution box there should be a Neutral bar and a PE bar, with one link between them. From the PE bar, there should be a PE wire going down to an Earth stake. Follow that wire to find the stake.

Is the building wired with ring mains or radials?

 

[sophiecentaur]

Does the armoured supply cable contain both Neutral and Active conductors?

Yes; just like all the underground supplies I have had before. There is a third (ground) wire alongside all neutral conductors ('twin and earth') indoors. Some lighting circuits were made with just twin conductors in the wiring. The consumer unit (as all others I have ever seen) has a neutral bus and a fused live bus.

The armour on the supply cable will be earthed at the supplier's end.

I assume that but it is not connected to my local earth network afaik. Without visibly interfering with the covering of the armouring, all I can do is to punch a small hole in the covering. The resistance between that and the house wiring earth is still high (k's) when I have finally made some contact with the armour.
The system is not what I have always been used to. As I said before, there has always been a strap around the incoming armour (four past houses) as a local earth. The last house had just two overhead conductors (no supply earth) and an earth spike plus a bigger / better one of my own.
Bottom line is that I could always (not conveniently) take an earth conductor from the distribution box / fuses to a spike outside. It's an old house and the services only appear inside the house. It's possible that the underground water supply pipe could now be plastic (replacing the old lead from 1930) So my question is really what's wrong with making use of the armour layer? You'd need to be familiar with the systems on UK. Of course, there are ring mains plus star connections to Cooker etc.. All pipes seem to be earthed with several straps.

I ask again whether the presence of a PV system could affect best practice.
I may have to bite the bullet and pay someone to look into it and fit an outside earth. Aamof, I will fairly soon be taking power to an outside workshop so I could kill two birds with one stone.

PS What is "VK7 Land"?

 

[Guineafowl]

a strap around the incoming armour (four past houses) as a local earth

That sounds like TN-S earthing. Max external earth fault loop impedance reading (Ze) is 0.8$\Omega$.

I’d certainly call someone in to verify your new house’s earthing system. If you get only L and N, you’d normally need your own earth rod, so-called TT earthing. Max Ze is technically around 200$\Omega$, but should be investigated if above 100$\Omega$, really. All circuits must be protected by an RCD, although a 30mA one is a poor choice for whole-house protection.

I doubt your RCD tripping is due to a too-high earth reading. If it’s a 30mA flavour one, it will, in theory, trip even if the earth loop is up to 1667$\Omega$, any higher and it would cause the opposite problem, ie not tripping when it should. Your socket tester (check the specs) might not be set up to check TT systems.

The RCD is reading earth leakage, so the task is to find out where that’s coming from, a fault or cumulative small amounts of ‘normal’ leakage from multiple circuits. That would involve, amongst other things, insulation resistance testing or live earth leakage measurements. Solar is a common culprit, and really should be served by a type ‘B’ RCD.

First move should be an inspection, perhaps an EICR, as it looks like there’s lots to unpick here.

***

Side-note:
I moved in to a new place a year ago, with big stables near the house, with an obviously DIY electrical supply. Earth loop at the sockets was up around 400$\Omega$! Substantially different from at the house DB, which was comfortably under the 0.8$\Omega$ expected from the TN-S earthing.

I traced the fault back to a junction box up on the chimney, where the earth was simply not connected. The earth conductor had been stripped back, and was the right length, but not inserted in the junction. It looked deliberate, and my bet was, the PO was experiencing RCD trips and so decided to ‘float’ the stables. Bizarre.

 

[Guineafowl]

Here’s a interesting document about socket testers:
https://www.electricalsafetyfirst.org.uk/media/1205/best-practice-guide-8-issue-2.pdf

It seems that, if anything, they might a little generous with the ‘earth ok’ light.

 

[Averagesupernova]

Im unfamiliar with the practices in the UK. However, the main thing to be concerned with is if the neutral has a solid connection to:

...all the metal bits in the house seem to be connected by a maze of earth conductors...

If some metal chassis is connected to a hot wire through some defect in an appliance then this effectively shorts the supply out and blows a fuse or trips a breaker. The system does not rely on the conductivity of the actual earth in this case.
-
It is important for the system to be referenced to the actual soil/earth. By not doing this it is possible for the whole system to float up and develop a dangerous voltage between the ground you stand on and anything attached to:

...all the metal bits in the house seem to be connected by a maze of earth conductors...

The concencus in the US sometimes seems to be that there is an excessive use of grounding/earthing rods. The small shed adjacent to the house that is fed through a breaker in the house requires a grounding/earthing rod. As far as I know, any stand-alone structure requires this regardless of what it's fed from. In the event that the neutral and protective ground/earth in the feeder that runs to this small shed is broken, the grounding rod will have a tendency to hold the metal chassis of anything electrical in the shed close to the same potential as the ground close to the shed. This reduces the chance of shock. It is redundant but often redundancy = increased safety.

 

[sophiecentaur]

However, the main thing to be concerned with is if the neutral has a solid connection to:

. . . . earth. The RCD would instantly blow for more than 30mA of imbalanced L-N current. Your N-E connection is not part of the UK system. N and L float with respect to the potential of the local Earth. The balance of the three phases from the local sub-station will determine the N volts (relative to Earth) at each single phase outlet in each house. The system floats when there's a difference between the loads on the three phases. There is little similarity to the terms and the arrangements in the US system.

It amazes me how many approaches and opinions there are about the basic function of the Earth connection. It surely has to limit the possible volts between two random pieces of metal and the amount of current that can pass between them (through a body). The earth path through a fault must also be low enough resistance to cause a fuse to blow - another safety feature.

My main concern is that there seems to be no local connection between my company earth (the armour) and anything in the house circuit. If there is, in fact, any local earth spike, I'd expect to measure (DVM) some low value of resistance. ( path between my earth - through the cable armour - to company transformer earth - back via the Earth. This, of course will not apply to where the supply is through two overhead conductors.

When I was a boy, we had a two wire supply (overhead) and no solid state technology. To deal with a fault to earth, the earth spike was connected to the house earth via an Earth Leakage Trip which tripped with a low(ish) current. Not low enough to avoid killing you but enough to deal with many equipment faults.

 

[Averagesupernova]

N and L float with respect to the potential of the local Earth.

This makes no sense in the context of this thread. If N and L are not referenced in any way then what is the point?

The earth path through a fault must also be low enough resistance to cause a fuse to blow - another safety feature.

Not possible. You cannot rely on the soil to blow a 20 amp fuse. Too much resistance. Unless what you mean is what I already said here:

Im unfamiliar with the practices in the UK. However, the main thing to be concerned with is if the neutral has a solid connection to:

all the metal bits in the house seem to be connected by a maze of earth conductors

If some metal chassis is connected to a hot wire through some defect in an appliance then this effectively shorts the supply out and blows a fuse or trips a breaker. The system does not rely on the conductivity of the actual earth in this case.

 

[sophiecentaur]

This makes no sense in the context of this thread. If N and L are not referenced in any way then what is the point?

Not possible. You cannot rely on the soil to blow a 20 amp fuse. Too much resistance. Unless what you mean is what I already said here:

You have made my point about the wide range of 'philosophies' involved with this topic.

I don't disagree with your points but I have actually dealt with them in my last post. The Earth Leakage trip (when I was a lad) dealt with heavy currents to earth where the earth loop resistance is high. That's the point of using the company Earth when available. I do not seem to have one connected.

The N voltage is always 'near zero relative to Earth (round about the mean values vector sum of the three phases. The "point" would be to understand the system. You can always measure a few N volts reference to earth.

The "context of this thread" has been ignored in most of the above posts; Any PF conversation about electrical power supply always seems to chase its own tail, rather than answering the point of the OP.

Third try: should I be concerned that the company armoured sheath appears to not be connected? Relevant replies from anyone with actual practical knowledge of PV installations would be appreciated because that might (?) change things. Is it the case that protection can only be achieved by active protection with a PV system.

 

[Averagesupernova]

So what happens if you connect a resistive load such as an incandescent light bulb between live and the metal chassis of some known good appliance that has all three pins? Will it trip an RCD somewhere? Will the bulb simply light normally or will it be dim due to the extra resistance of the soil? I can't really make heads or tails out of what the actual problem is. I'm not 100% sure where the device is that detects the imbalance between live and neutral. You have a tendency to be more than willing to state that there are a wide range of varying philosophies yet I never get a solid answer about how things are SUPPOSED to be done over there in the UK. You cannot expect good answers from misinformed people. I suspect the reason I never get a straight answer is because things are a little looser than we here in the USA are lead to believe. From what I've noticed folks from the UK seem to think it's a Wild West that anything goes concerning our system in the USA. There are people who will always diddle with something they have no business messing with but that cannot be blamed on the standard we try to adhere to.

 

[Guineafowl]

Third try: should I be concerned that the company armoured sheath appears to not be connected?

I’d say you might be on a TT or TN-C-S system (see below), so in that case, no, but we can’t be sure yet. I also can’t yet explain your high k reading between supply cable armour and your earth, except to suggest inadequate earthing at your end.

- Can you post a pic of the service head?

- Where does the main earth wire to your house DB come from? It should be thick, 6mm2 or bigger. You might follow red herrings to a metal water or gas pipe, known as main bonding conductors. The maze of interconnecting earths are supplementary bonding. If you don’t find a dedicated earth rod, and are on TT, you need one.

***

Hopefully to clear up some uncertainty, here are the three main earthing types in the UK. Number three is by far the most common; the other two being old relics:

1. TT.
You get L and N only, and fit your own earth rod. Earth loop perhaps 100$\Omega$, too much to pop MCBs and fuses reliably, so the whole installation must be protected by RCDs. Mainly older, remote rural properties.

2. TN-S.
You get L, N and E, the latter usually via incoming cable lead (as in Pb) or armour sheath. Earth loop max 0.8$\Omega$. Mainly older properties. My favourite type of earthing.

3. TN-C-S.
You get L and PEN (combined Protective Earth and Neutral, aka CNE).
At the service head the PEN is split into N and E, presumably the N/E link being discussed above. Max loop 0.35$\Omega$. Sometimes referred to as one of its forms, PME, Protective Multiple Earthing.

 

[Averagesupernova]

I’d say you might be on a TT system, so in that case, no, but we can’t be sure yet. I also can’t yet explain your high k reading between supply cable armour and your earth, except to suggest inadequate earthing at your end.

- Can you post a pic of the service head?

- Where does the main earth wire to your house DB come from? It should be thick, 6mm2 or bigger. You might follow red herrings to a metal water or gas pipe, known as main bonding conductors. The maze of interconnecting earths are supplementary bonding. If you don’t find a dedicated earth rod, and are on TT, you need one.

***

Hopefully to clear up some uncertainty, here are the three main earthing types in the UK. Number three is by far the most common; the other two being old relics:

1. TT.
You get L and N only, and fit your own earth rod. Earth loop perhaps 100$\Omega$, too much to pop MCBs and fuses reliably, so the whole installation must be protected by RCDs. Mainly older, remote rural properties.

2. TN-S.
You get L, N and E, the latter usually via incoming cable lead (as in Pb) or armour sheath. Earth loop max 0.8$\Omega$. Mainly older properties. My favourite type of earthing.

3. TN-C-S.
You get L and PEN (combined Protective Earth and Neutral, aka CNE).
At the service head the PEN is split into N and E, presumably the N/E link being discussed above. Max loop 0.35$\Omega$. Sometimes referred to as one of its forms, PME, Protective Multiple Earthing.

I see. This explains the confusion and seemingly contradictory explanations I have experienced in the past.

 

[Averagesupernova]

1. TT.
You get L and N only, and fit your own earth rod. Earth loop perhaps 100Ω, too much to pop MCBs and fuses reliably, so the whole installation must be protected by RCDs. Mainly older, remote rural properties.

This is the one that confuses me. If it is expected that an RCD will trip, the system must be referenced to a ground rod someplace. The grounding wire attached to the chassis of appliances is attached to the customer supplied ground rod as I understand. Well and fine but if the line and neutral are truly floating then there is no possible path for shock current. If it's truly floating then touching live while standing on the ground simply causes the live wire to be connected through the person's body to the earth. No shock will occur since there is no return path in a floating system. If then at the same time someone touches the neutral then current will pass through both people. What's interesting in that case is that an RCD would still not trip since the currents still have to be equal. For the RCD to work the neutral has to be referenced to the earth somewhere and I assume it's at the transformer.

 

[Guineafowl]

For the RCD to work the neutral has to be referenced to the earth somewhere and I assume it's at the transformer.

Yes, in all three systems the neutral/PEN is earthed at the transformer end.

 

[Averagesupernova]

Yes, in all three systems the neutral/PEN is earthed at the transformer end.

Ok. Makes sense. So line and neutral do not float.

 

[Guineafowl]

One further thought, @sophiecentaur , is that your PV installation should have involved some basic electrical tests on the existing supply.

Did the PO leave behind some paperwork with regard to this? It should be in the form of an electrical test certificate, detailing earthing system and Ze reading.

Failing that, the PV company should have left some stickers with their contact details. They might have the certs on file.

 

[Baluncore]

What's interesting in that case is that an RCD would still not trip since the currents still have to be equal. For the RCD to work the neutral has to be referenced to the earth somewhere and I assume it's at the transformer.

If the active current is not equal and opposite to the neutral current, then the RCD will trip.
PE and N are linked in the distribution box, and for MEN, on every pole along the street. That is necessary to protect all the insulation.
But earth is not necessary, the trigger could be conduction to another A or N circuit on another RCD.

 

[Guineafowl]

PE and N are linked in the distribution box

I’d have to add (see post #11) that this is not the case for TT and TN-S installations.

 

[sophiecentaur]

I'm not 100% sure where the device is that detects the imbalance between live and neutral.

Look at the diagram at the top of the wiki article.An RCD can be placed anywhere in the circuit - on the feed to one load - on a group offload - or the whole input to the house. It's a current transformer. Both L and N go through a core are 'two primaries' and the secondary has many turns which feed an amplifier. Normally the L and N currents are equal and opposite but any imbalance (say 30mA or 10mA) will be detected via the secondary.

So what happens if you connect a resistive load such as an incandescent light bulb between live and the metal chassis of some known good appliance that has all three pins?

If the L and N currents are not equal because there's an alternative return path (not the N) the RCD will trip. This is not new technology; I fitted one fifty years ago.

Where does the main earth wire to your house DB come from?

This has been my point; I don't know (as I thought I'd made clear)..

In four of my past houses (with underground feeds) they all had a visible, chunky connection to the sheath of the armoured cable which supplied a good very low potential to all metal in the house. There was never an issue of a failed 'earth loop test' because there was an excellent ground connection to the substation.

My one house with just two wire overhead connection had visible earth spikes but the earth resistance was only 'ok' but apparently it was acceptable.

 

[Guineafowl]

This has been my point; I don't know (as I thought I'd made clear)..

Ok. It’s hard without being there or seeing pictures, that’s all. Does it dive into the wall, where do you lose sight of it?

In any case, if it doesn’t connect to the service head (earthing types 2 and 3 above), then you have TT earthing. If you can’t find the rod, next stage is a live loop impedance test (Ze). This should have been done before the PV was installed.

With regard to the PV, any earthing type 1-3 is suitable, as long as it’s within spec. After verifying your earth, I would then start chasing the RCD trip.

- What circuit(s) does it serve, when does it trip, etc.

- Visual inspection as far as possible, especially junction boxes and outlets.

- For the PV part, isolate AC and DC sides, then IR test individually.

***
Side note - my PV was tripping during rain when I moved in. Proceeded as above, and found an unsealed junction box outside the house, full of insect debris and cobwebs that were getting damp.

 

[sophiecentaur]

Ok. Makes sense. So line and neutral do not float.

With respect, the N conductor is never at 0V ground potential, even in the best systems. A 'scope always shows a few volts of 50Hz relative to earth. In my book, that could be 'floating'. You could say that VN doesn't 'float' between the N and E, right next to the transformer but you can see it happening with a DVM.

In UK homes, it's forbidden to connect N to E. Why would that be if it were not relevant?

Many decades ago, it was decided that a single conductor was not the way to go and that a low (near zero) voltage neutral would be optimal. This is for a three phase stystem and the advantage is that it allows a degree of old balancing among the loads on the three phases. Conventional power distribution to houses in UK is to spread the phases 1,2,3,1,2,3,1,2,3 to a row of houses and statistics does the rest.

Ok. It’s hard without being there or seeing pictures, that’s all. Does it dive into the wall, where do you lose sight of it?

True. The head consists of an armoured cable, emerging from the floor with just two conductors coming out at the top. There's no other box / sleeve / clip attached. Trust me; I know what I'm looking for and there seems to be nothing like an earth connection. Your comments show that you are aware of of my confusion and concern, particularly in the light of the PV installation. Problem with the (whole) house is the various legacies we discovered when we moved in; the electrics was just one of them. The last owner died four years ago and he would have had many of the answers. Unfortunately, he died whilst walking up to the Pub (which say it all; everyone loved him, though.

As mentioned, I'm having 'a man' to look at it today and to decide what we should do. He may know where to look for a possible earth installation. Unfortunately there's a lot of concrete close in to the house and that's unlikely to be a good place for an earth spike.

. For the RCD to work the neutral has to be referenced to the earth somewhere

It's true that there has to be a path other than between the L and N. But a current transformer knows nothing about anything but the net L and N currents. I guess Kirchoff applies so the net current flow at any node must be zero. But the RCD will spot any difference and doesn't care about the nature of the extra path.

I feel like I'm in a space ship with no handy local earth connection. Never had any suggestion of a shock, though.

 

[Guineafowl]

In UK homes, it's forbidden to connect N to E. Why would that be if it were not relevant?

I’m not sure what you mean by this - in the common TN-C-S system they are linked. Unless you mean YOU are forbidden from doing it, which would be true - the service head belongs to your DNO (Distribution Network Operator), and changing the earthing system would require permission from them and a building warrant.

As mentioned, I'm having 'a man' to look at it today and to decide what we should do. He may know where to look for a possible earth installation. Unfortunately there's a lot of concrete close in to the house and that's unlikely to be a good place for an earth spike.

Please let us know what happens! If he agrees it’s TT, and the readings aren’t good enough, and the earth rod can’t be found, I suspect he’ll sink a little earth pit in the concrete and bang one or two rods in.

 

[Averagesupernova]

But earth is not necessary, the trigger could be conduction to another A or N circuit on another RCD.

Both you and @sophiecentaur seem to be missing my point. Of course I realize that an RCD works by sensing unequal currents in the live and neutral. Those currents will NEVER be unequal if the system is completely floating. The system has to be referenced to something else (the earth) upstream of the current transformer of the RCD in order for the system to allow an RCD to work correctly.
-
Edit:
I do see your point about a pathway between two different RCDs on the same system would cause a trip on a truly floating system. This in my opinion is not safe enough.

 

[sophiecentaur]

Those currents will NEVER be unequal if the system is completely floating.

I agree but how can you expect to find a perfectly floating system? All the circuit diagrams of mains supplies show substation transformers with a Neutral connected to earth. That gives a possible path to the transformer neutral via the path through earth. Even a high resistance earth fault path will allow lethal current to flow.

We, of course, are saying the same things about this. Stating a problem without any misunderstandings is hard and can turn into a dialogue of the deaf. Not uncommon in PF.

 

[davenn]

PS What is "VK7 Land"?

Ahhh, you are not a amateur radio operator

VK7 is the callsign prefix for Tasmania, Australia,
I am in VK2 = NSW state .... VK2TDN

Dave

 

[Averagesupernova]

I agree but how can you expect to find a perfectly floating system? All the circuit diagrams of mains supplies show substation transformers with a Neutral connected to earth. That gives a possible path to the transformer neutral via the path through earth. Even a high resistance earth fault path will allow lethal current to flow.

We, of course, are saying the same things about this. Stating a problem without any misunderstandings is hard and can turn into a dialogue of the deaf. Not uncommon in PF.

The point is that as far as I can remember on this forum I have never gotten a straight answer as to how the electrical system in the UK was done concerning grounding. You said yourself:

N and L float with respect to the potential of the local Earth.

But, apparently not according to others and you also said:

All the circuit diagrams of mains supplies show substation transformers with a Neutral connected to earth.

Now concerning a floating system to remain completely isolated, we don't need to worry about it since it's likely never done except in special cases. But, there are plenty of places the system is small enough that it's entirely possible that it could remain isolated for years. At any rate, I would not consider it safe without something in place for monitoring isolation. Here's an example. The video covers some things that are pretty basic to most of us but still worth watching.
-

 

[sophiecentaur]

I’m not sure what you mean by this - in the common TN-C-S system they are linked. Unless you mean YOU are forbidden from doing it, which would be true - the service head belongs to your DNO (Distribution Network Operator), and changing the earthing system would require permission from them and a building warrant.

Please let us know what happens! If he agrees it’s TT, and the readings aren’t good enough, and the earth rod can’t be found, I suspect he’ll sink a little earth pit in the concrete and bang one or two rods in.

I dug around in the conveyancing documents and actually found a 'sparse' report on electrical systems. It suggests that I have a TT system. This link has some interesting figures, including the fact that earth resistance can vary a lot , according to temperature and ground saturation, and be over 1kΩ. Bottom line (to me) is that active protection is essential. Fine, but something that's inherently safe(r) would make me happier.

Q. is my electrician likely to be prepared to connect my earth to the armoured cable? Seems like a no-brainer.

 

[Guineafowl]

Q. is my electrician likely to be prepared to connect my earth to the armoured cable? Seems like a no-brainer.

Unlikely.

- Service head belongs to your DNO.
- Meter belongs to your energy company.
- Anything after that belongs to you, and you or your electrician can play with it.

Secondly, going from TT to TN-S, you are changing from customer-supplied earth, to one supplied by the DNO and which they are responsible for. You’d need their permission and they’d probably send their own installer out.

That said, it’s worth asking. TN-S is best, followed by TT. TN-C-S can cause problems with outbuilding supplies and car chargers (search ‘broken PEN conductor’).

 

[sophiecentaur]

Unlikely.

- Service head belongs to your DNO.
- Meter belongs to your energy company.
- Anything after that belongs to you, and you or your electrician can play with it.

Secondly, going from TT to TN-S, you are changing from customer-supplied earth, to one supplied by the DNO and which they are responsible for. You’d need their permission and they’d probably send their own installer out.

That said, it’s worth asking. TN-S is best, followed by TT. TN-C-S can cause problems with outbuilding supplies and car chargers (search ‘broken PEN conductor’).

Thanks for the info and opinion. Something that I can't understand is how this house has T-T earthing. I'd bet money on finding the armoured cladding connected to house earth system in any random house I looked in our street. It's the only arrangement I have ever seen except in our last house with two overhead conductors.

I don't know how many generations of electricity supply have been installed since the house was built in 1930 but how come the PV installers didn't raise the problem ten years ago?
I found a record of earth loop resistance of 130Ω which would be lethal with just 2A current flowing and no fuse blown. Can any supply company argue against making 'that earth connection' and reducing the resistance to 1Ω?

As an aside, I notice that an 'island connection' is used for a EV charging points and protection is just local to the charger. Also there are special considerations for protection of hot tubs etc. with a requirement for a 10mA RCD. A real toaster in the bath situation, potentially.

 

[Guineafowl]

I don't know how many generations of electricity supply have been installed since the house was built in 1930 but how come the PV installers didn't raise the problem ten years ago?
I found a record of earth loop resistance of 130Ω which would be lethal with just 2A current flowing and no fuse blown. Can any supply company argue against making 'that earth connection' and reducing the resistance to 1Ω?

The PV installers wouldn’t have seen a problem - 130Ω is within spec for TT. Don’t forget the RCD requirement.

I can’t explain why you’re not TN-S - perhaps the earth loop impedance (as it’s called, although I was scoffed at on here for doing so!) was above the 0.8Ω max due to poor connections or long cable run.

 

[sophiecentaur]

The PV installers wouldn’t have seen a problem - 130Ω is within spec for TT. Don’t forget the RCD requirement.

I can’t explain why you’re not TN-S - perhaps the earth loop impedance (as it’s called, although I was scoffed at on here for doing so!) was above the 0.8Ω max due to poor connections or long cable run.

I had an interesting chat with a guy in UK Power Networks. He saw my problem.

He did say that the supply may never have been changed since 1930 and that could explain why TT is there. He will send engineers to look at the system and they may well fit a termination to the armoured sheath. However, it appears that not all installations 100 years ago used a metal (lead) sheath so I can't get my hopes up too high.

Another thing. I was talking to my neighbour and she let me look at her installation. Despite having been re-wired not long ago, it still has a TT system. But the installers presumably measured an 'acceptable' earth impedance so no one wanted to fix it. She was worried, of course but I told her she's legal and that I'm just fussy.

The UPN service is FREE though!

 

[Guineafowl]

I had an interesting chat with a guy in UK Power Networks. He saw my problem.

He did say that the supply may never have been changed since 1930 and that could explain why TT is there. He will send engineers to look at the system and they may well fit a termination to the armoured sheath. However, it appears that not all installations 100 years ago used a metal (lead) sheath so I can't get my hopes up too high.

Another thing. I was talking to my neighbour and she let me look at her installation. Despite having been re-wired not long ago, it still has a TT system. But the installers presumably measured an 'acceptable' earth impedance so no one wanted to fix it. She was worried, of course but I told her she's legal and that I'm just fussy.

The UPN service is FREE though!

Keep us posted!