120V from water tap to true earth

[Midwest]

The other night, neighbour knocked my door. She said she'd gone to use their outdoor tap, and she thought she'd got a shock. Went and had a look, and they have one of those Rolec tap pods, with combined water tap and electrical socket. I've not been trading for a few years now, but I got out my MFT to do a Zs test on the socket. However, it wouldn't carry out the test, and came up with 'CONN', which in the past I knew that was either a connection problem or voltage on cpc. Got the same result on socket in house, my MFT then went out on flat battery.

I then got my voltage tester, and from tap to extension lead (neutral), I got 120V, same in house. No SFCU for Rolec pod. I'd taken boots off to go in house, but thought I'd just unscrew pod lid to see what was going on inside. You guessed it, got belt from tap

At this point, I suggested we isolate that particular RF & call out DNO (PME supply I'm thinking lost neutral). Didn't want to turn off RF, large chest freezer in garage. But she did call out DNO. Following morning before I went to work I knocked the door. DNO checked their supply & main earth, all good. They made her turn off RF; she ran extension lead from 1st floor RFC (didn't think of that). Suggested calling an electrician I knew, but she was going to wait for hubby to come home from Town that evening.

Anyhow, when I got home from work, hubby had been on the case for a few hours, and he reckoned he found the fault. Dodgy Wago connector on earth somewhere. He's had an outdoor extension, with electrics done, either by him or Bob the Builder.

My question, could a poor earth connection, cause a potential between earth and true earth?

 

[Vortigern]

Last time I got that sort of voltage on earth, somone had crossed over neutral and earth.

 

[Midwest]

I‘m just a bit concerned he hasn’t rectified the fault. I don’t want to get too involved, but fault is quite dangerous. Might just offer to do Zs test again.

 

[timhoward]

Various thoughts are flowing….
1 is the the RFC rcd protected and does the rcd work. A N and E crossover ought to upset an rcd. It sounds like more than one fault combined internally.
2 if PME supply and voltage of 120v between N and a pipe then it suggests to me that pipe can’t be bonded all the way back the MET and service head where N and E are joined anyway.
Some tests with a wander lead between MET and pipework might be an idea.
3 yes I’d definitely knock on the door and test again. You could legitimately say that it can affect neighbouring properties due to bonding.

 

[DPG]

Various thoughts are flowing….
1 is the the RFC rcd protected and does the rcd work. A N and E crossover ought to upset an rcd. It sounds like more than one fault combined internally.
2 if PME supply and voltage of 120v between N and a pipe then it suggests to me that pipe can’t be bonded all the way back the MET and service head where N and E are joined anyway.
Some tests with a wander lead between MET and pipework might be an idea.
3 yes I’d definitely knock on the door and test again. You could legitimately say that it can affect neighbouring properties due to bonding.

Re point 2, I suppose if it's a plastic incomer then it may well not be bonded anyway.

 

[Lucien Nunes]

If it were a broken CNE in the supply then 120V CPC - true E would mean only 110V L - N, so most of the appliances in the house wouldn't work properly and those voltages would very with any changes in load. Testing tap - N would show minimal voltage as all neutrals and CPCs would be floating to the same voltage together. A quick test would be to run a Zs measurement with the green and black test leads both to N, which will fail if the CNE is open but pass if only the CPC is open.

A floating CPC will drift up to somewhere between 0 and 230V according to the ratio of functional leakages into and out of it. Symmetrical suppressor capacitors in appliances especially white goods and large SMPSUs tend to pull the CPC midway between L & N. But in the absence of functional leakage the behaviour of the cable dominates and its much greater stray capacitance from CPC to true earth than to line tends to pull the CPC down towards earth.

Therefore on a long circuit with few appliances connected I would expect a floating CPC to take up a few tens of volts and deliver very little current when discharged to earth. The CPC of a circuit with less total cable length and multiple high-leakage loads would tend more towards 100V or more and have a lower source impedance i.e. more leakage current would flow into a connection to earth. This sounds like the present situation but I would be concerned that if a Wago connection is faulty there might be more hidden issues.

 

[Midwest]

Thanks for your replies. This Rolec pod tap, is earthed by a plate to the socket cpc. I expect the feed water pipe will be copper (couldn’t see it), but main supply is plastic. We are new builds, so CU is dual rcd.

I’m not sure what’s been done in the extension and by whom, which is a concern. But her indoors won’t want me to get too involved. So might just suggest I do Zs test at the Rolec pod.

 

[UNG]

Can't help but feel there is more to this when the neighbour spends a few hours and eventually identifies the fault as a dodgy earth connection at a Wago connector was this by trial and error or by proper faultfinding with the appropriate test equipment.
Makes you wonder how long that fault has been present and how good the rest of the electrical installation is and whether it has been properly tested to ensure it is safe

 

[nicebutdim]

Can't help but feel there is more to this when the neighbour spends a few hours and eventually identifies the fault as a dodgy earth connection at a Wago connector was this by trial and error or by proper faultfinding with the appropriate test equipment.
Makes you wonder how long that fault has been present and how good the rest of the electrical installation is and whether it has been properly tested to ensure it is safe

The neighbour knew what the likely cause was, and where it could be found, as he created the problem. Maybe it was a one off or maybe there are a heap of problems waiting to occur.

 

[Midwest]

Can't help but feel there is more to this when the neighbour spends a few hours and eventually identifies the fault as a dodgy earth connection at a Wago connector was this by trial and error or by proper faultfinding with the appropriate test equipment.
Makes you wonder how long that fault has been present and how good the rest of the electrical installation is and whether it has been properly tested to ensure it is safe

The existing install will be fine; I've had work done to mine and it was okay.

I converted my garage, and needed planing permission. They've converted their garage, I know they've not applied. But I know lots of people around here done the same. The Rolec pod was installed with the original house build, but the alteration to the garage was done by them.

Will try and make casual contact over the weekend.

 

[LastManOnline]

My question, could a poor earth connection, cause a potential between earth and true earth?

Yes it could.And modern appliances with their built in electronics will quickly alert you to your poor earth as soon as you are unfortunate enough to make contact with the affected metal while standing on a poorly insulated floor or worse while simultaneously touching other metal that is well earthed/bonded.

 

[Midwest]

Yes it could.And modern appliances with their built in electronics will quickly alert you to your poor earth as soon as you are unfortunate enough to make contact with the affected metal while standing on a poorly insulated floor or worse while simultaneously touching other metal that is well earthed/bonded.

Would it reach 120V though?

 

[LastManOnline]

Would it reach 120V though?

Good question.I personally never measured a voltage that high that resulted from a disconnected CPC on a circuit containing appliances with intentional leakage built in.

Looking at the problem from another angle ,it would appear that the homeowner solved the issue by reconnecting an earth wire that had become loose.Is it possible he has been using an earth wire as a return wire? (As a neutral).The disconnected earth wire would then act as a "broken neutral" causing a voltage to appear on it.

 

[James]

In the U.K. a broken N will rise to 230v if there is any load on the circuit after the break.

 

[Vortigern]

Errmm can a load be on the circuit after the break, it would be dead from the break onward??? When I started learning it was Live and Neutral, and then of course earth which was really just another neutral. Then I was told, there is no neutral now, it is all phase right the way back to the star point. Okayyyy, I took that on board then understood that a broken neutral is live. Well of course it is because in truth, it is all phase. With me so far?

 

[LastManOnline]

In the U.K. a broken N will rise to 230v if there is any load on the circuit after the break.

Correct.But in the case of the OP where it appears some unconventional electrics has been carried out I,m wondering how could reconnecting an earth possibly lead to the voltage on earthed metalwork been removed?The only examples I can come up with are..

1) intentional earth leakage belonging to the affected circuit.

2) The earth wire has been used as a return wire and is now in effect " a broken neutral" .However as it's an earth wire it may be connected with other metalwork that offer some alternative but high resistance paths to ground.This would cause a volt drop.Entirely speculation on my part

 

[Midwest]

Firstly I must add, I cannot be certain the electrical additions have been carried out by my neighbours or anyone not competent. Also the main supply has been verified as in order by the DNO.

Therefore the fault was somewherein the property, could of been in the addition or possibly in the existing, although you’d of thought that would of been found by the original EIC, but you never know.

Neighbours appear to have gone away for the weekend, so been unable to offer Zs test at pod. Her indoors is saying not to get involved. I’ll see, and perhaps pick my moment. But he is a bit of a very confident type, if you get my drift.

 

[LastManOnline]

I

Neighbours appear to have gone away for the weekend, so been unable to offer Zs test at pod.

I, m progressive leaning towards the possibility there is actually nothing wrong and you could end up trying to fix something that is, nt broken.
The DNO found nothing wrong with the supply or the earthing.
They isolated the problem to the ring.
The issue was solved when the loose earth was reconnected.

Where does that leave us?
Neither the homeowner nor yourself mentioned that any appliances had stopped working,which confirms the integrity of Land N and rules out one of my previous suggestions about the earth been used as a, return wire.
That brings us back to intentional earth leakage from one (or more) of the appliances.The circuit for this current has now been opened, creating a "broken neutral" type scenario. This voltage will appear on all class 1 appliances and metalwork connected to them on the affected part of the circuit.

The above is easily established by plugging out all appliances and isolating all fixing appliances on the ring. Disconnect the earth that caused the initial problem. Test at the tap and it should be volt free. Plug the appliances back in progressively, testing as you go and you should find the 120 volts reappearing on the tap.

I have experienced the above problem on several occasions