Neutral - Earth voltage

[Bob556]

Hi everyone
I've had an external socket fitted so I can use the lawnmower without an extension lead.

It was fitted whilst I was at work, and although the electrician convinced my wife the socket was working (showed her the leds on the socket switches) when I came to use it, it was dead. LEDs were on but couldn't get any power not even for a light bulb (old 60W incandescent and CFL - both checked as working.)

I asked the guy to come back and he said he would, but didn't. Long story short, he gave various excuses then said he was going on holiday. So, it's been fitted 4 weeks and I've given up on him.

SET-UP
He took a spur off an interior socket, to a switched FCU, then through the wall to a plastic junction box, then used tough cable to the socket (because I didn't want conduit on the wall.)

MY CHECKS
The LEDs go on/off with the switches, and with the FCU.
A neon pen showed there was voltage at the socket, JB and FCU.
I used a voltmeter to check voltage at the socket, it was 190-195V between LIVE and NEUTRAL . It was the same at the JB and the FCU but was 240-242V at the parent socket and at another socket nearby.

After close inspection, I found the live and neutral wires were not making very good connections in the FCU. They looked OK, but were actually just resting against the terminal and not screwed in. I put them in, tightened them up and checked voltage again. This time, it's 240-242V between L - N and also L - E. But I'm also getting 40 - 45 V between N-E.

(The socket now powers the aforementioned lamp!)

On the other sockets, I'm getting the same 240V (ish) voltage for L - N and L - E but zero N-E

So, where should I look for causes of the N-E voltage?

 

[Adam_151]

I suspect the earth is open cirucit, or very high resistance. With the power off do a continuity test between earth on the new socket, and a long lead to something you know has a good earth. If your consumer unit is metal, then the lid cover fixing screws are a good place to go back to.

Its a waste of time asking if he left you a minor works cert isn't it....

 

[JohnW2]

After close inspection, I found the live and neutral wires were not making very good connections in the FCU. They looked OK, but were actually just resting against the terminal and not screwed in.

Goodness. Are you sure that this 'electrician' was an electrician?

I put them in, tightened them up and checked voltage again. This time, it's 240-242V between L - N and also L - E. But I'm also getting 40 - 45 V between N-E.

There's something wrong with those measurements. If the L-N and L-E voltages are both roughly the same, then the N-E voltage must be roughly zero.

It's just simple arithmetic. If the top of one lighthouse (cf N) is about 240 feet above sea level (cf L) (so that L-N=240) and the top of another lighthouse (cf E) is also about 240 feet (so that L-E=240), then the difference between heights (above sea level) of the two lighthouses (N-E) must be about zero.

Returning to the actual situation, if the N-E voltage really were 40-45V and the L-E voltage were 240V,then the L-N voltage would only be about 395-400V.

(The socket now powers the aforementioned lamp!)
On the other sockets, I'm getting the same 240V (ish) voltage for L - N and L - E but zero N-E
So, where should I look for causes of the N-E voltage?

As above, it seems that there's something wrong with your measurements. What are you using to measure them?

Kind Regards, John

 

[plugwash]

Strictly speaking AC is 2 dimensional, so it's not imposible for voltages to form a "triangle", It would be pretty weird in a case like this though. Measuring a voltage can also change said voltage.

That said I think the most likely explanation for the OP's readings is an intermittent connection.

 

[JohnW2]

Strictly speaking AC is 2 dimensional, so it's not imposible for voltages to form a "triangle", It would be pretty weird in a case like this though.

You mean if the voltages were not all in phase with one another? If so, that surely would not be merely 'wierd', it would actually be impossible in the situation we're talking about, wouldn't it?

Measuring a voltage can also change said voltage.

It can. As I said, there appears to be something 'wrong' with his measurements. However:
(a) it's very likely that he is using a very high impedance meter.
(b) even if it were a low impedance meter, that would, in some circumstances reduce the voltage being measured, but I can't see how any meter could raise a voltage being measured.
(c) if the earth were 'floating', then it could pick up (capacitively) enough for a high-impedance meter to show a 40V N-E p.d. However, if that were the situation, I would think it would be incredibly unlikely that one would get identical L-N and L-E voltage measurements.

That said I think the most likely explanation for the OP's readings is an intermittent connection.

If you mean an intermittent connection such that the voltages (particularly the N-E one) were actually different when he measure the N-E one from when he measured the L-N and L-E ones, then that's certainly a possibility. However, if (as I think he has implied) he is consistently getting the results he reported, that would require some co-incidences which would be essentially 'beyond belief'!

As has been suggested, measuring voltage between neutral and a 'definite earth' (not the CPC at the socket) might shed some light on what is going on.

Kind Regards, John

 

[ericmark]

My loop impedance tester failed, and I have thought of buying a cheap tester

however even the cheap one is £50, and pass mark is too high for a ring final.

I have considered ways to test, however at 30 mA the RCBO will trip, and the volt drop at under 30 mA would be very hard to measure, likely why the loop impedance testers are so expensive.

I suppose one could use a low ohm meter that uses the required 200 mA between two socket earth pins, with power off, or with main isolator off but MCB/RCBO off between neutral and earth at the socket, but it seems clear there is an error, so really no point, some how the fault needs correcting, and if you have the skill, then why did you use an electrician to do the work?

You know there is a fault, that's clear, and you don't feel you have the skill required or you would have not used an electrician to start with, and seems likely a electrical minor works certificate has not been completed or the electrician would have found the fault, he is clearly a poor electrician to have done the work without testing, so you would not want him back, so only thing you can do as far as he is concerned is report him to his scheme provider.

The question is do you report him before or after you get another electrician to fix it? I would say before, so the scheme can come and inspect his work, but you have already corrected some faults, so it would be hard to show what was due to his poor workmanship, so seems likely only option is to just get another electrician to fix it, you could try sending the first one the bill. Although I can't see you getting any money back.

You can report to trading standards, but again since you have corrected some faults, can't see you getting much help there.

 

[Murdochcat]

The original electrician should have given you a minor works certificate

 

[JohnW2]

The original electrician should have given you a minor works certificate

That has already been implied. However, if this person does not tighten up terminal screws, I doubt whether he issues any certificates, either!

In any event even if there were a cert., I don't think it would help to answer the OP's questions.

 

[Bob556]

First, thank you everyone for your comments, they're all appreciated.

To reply to some in reverse order,
ericmark, I appreciate your efforts, but you make some assumptions that are a bit wide. I am competent to fit another socket but chose to use an electrician for several reasons
1) I'm busier than usual at work and didn't want the extra work of DIY (that didn't work out very well!)
2) due to an accident, I don't have full use of a few fingers in one hand. It's not permanent but holding fiddlly screws and wires was not an attractive thought, and I was right. My fingers don't always do what I want them to, or what I think they're doing. It made fixing this problem much more difficult than it should have been.
3) I thought it would be good to do things the 'right way', you know with a minor works cert for when we sell the house in a year or two. That didn't work out very well either.

But you weren't to know these things.

In terms of reporting him.... Trading Standards don't accept direct complaints, you have to go through CAB. They take 5 days to respond, then they make the report.... I preferred to sort the problem out in case it eas/became a danger. I'm not sure who he's registered with and I dying think there's much point in asking him now.

JohnW2 and the others who commented on the readings. I used a digital multi-meter (after I got a new battery). It's quite old but kept safe. I took each reading several times and got consistent readings. I used the probes which have a very small contact area, and putting them on the terminal screws may not have given the best contact, but as I said, consistent results. There may also have been some oxidation in the lead contacts even though I did clean them. Even so, these problems wouldn't have created a 45V between NE, they would have reduced the reading if anything (someone may have said something similar.

I am glad that you all agree the readings are 'strange'! Also JohnW2 I'm told he is an electrician - by the person who recommended him, and by him himself. But you can have all the qualifications in the world its how you use them that matters, and as for experience... 30 years experience of doing something badly isn't very useful!

This morning, after reading your comments I repeated the tests using crocodile clips on the probe to increase contact area.
For parent socket, I got 243V LN and LE 0V NE
For FCU I got 243V LN and LE. AND 0V NE! Ie identical.

I don't understand that, but I took all readings several times. The FCU NE I took at least a dozen times because access to the terminals is very difficult and I didn't believe I was actually touching the N terminal. But, I got a reading on LE, and keeping the clip touching the E terminal, I touched the N, lifted off, touched again and again and each time got 0V. I don't understand it.

I suspect the earth is open cirucit, or very high resistance. With the power off do a continuity test between earth on the new socket, and a long lead to something you know has a good earth. If your consumer unit is metal, then the lid cover fixing screws are a good place to go back to.

OK, I wondered about this. I checked all the terminals when I checked things even those I didn't touch. I wondered how I could do a continuity test. I ended up using a old power strip that has a long lead. I took the cover off and clipped the test lead to the earth busbar then plugged it into the parent socket. I tested for continuity between parent socket and FCU earth terminals - no problem, showing as continuity on my meter and a resistance of 0.04ohm.i did the same with the parent socket and another socket, and the FCU and the same other other socket, again continuity with same resistance. I did these checks first as it was raining outside. I got the same result between the external socket and the FCU, parent socket and the other socket, so I'm confident that there is continuous earth.

For good measure, after I put all the switch plates back on, I did the same test using the power strip and the face plate screws and got readings of about 0.8ohm
So, I'm sure there is earth continuity between all new parts and the house. (and the new socket works!)

Where the first NE readings came from, I have absolutely no idea. I am sure I took the reading correctly but possibly, due to the limited access I may have been touching something else as well as the intended terminal. Maybe there was a stray clipping of wire in there. I have no idea whatsoever.

What I'll do next is buy a socket tester with RCD function (let's face it, any tests he may have done can't be relied on) and check that the RCD is tripped from the new socket (and a few others) and I'll monitor the socket for a while as I don't don't like mysteries like this strange NE voltage.


If anyone can suggest other tests for safety I'm interested

Its a waste of time asking if he left you a minor works cert isn't it.

Haha, he promised to bring it with him....

 

[Murdochcat]

If the installer had done any tests he would have realised there was a problem …..

 

[JohnW2]

JohnW2 and the others who commented on the readings. I used a digital multi-meter (after I got a new battery). It's quite old but kept safe. I took each reading several times and got consistent readings. I used the probes which have a very small contact area, and putting them on the terminal screws may not have given the best contact, but as I said, consistent results.

That's what I imagined.

There may also have been some oxidation in the lead contacts even though I did clean them. Even so, these problems wouldn't have created a 45V between NE, they would have reduced the reading if anything (someone may have said something similar.

As you say, it';s extreme hard to think of any way in which 'poor contact' could have have resulted in the meter indicating voltages 'that were not there'.

This morning, after reading your comments I repeated the tests using crocodile clips on the probe to increase contact area.
For parent socket, I got 243V LN and LE 0V NE
For FCU I got 243V LN and LE. AND 0V NE! Ie identical.

So, are you saying that the 'apparent problem has 'gone away'?

Where the first NE readings came from, I have absolutely no idea.

I fear that none of us maynever know the answer to that !

I am sure I took the reading correctly but possibly, due to the limited access I may have been touching something else as well as the intended terminal. Maybe there was a stray clipping of wire in there. I have no idea whatsoever.

It is, indeed, very difficult to think of any possible explanation.

What I'll do next is buy a socket tester with RCD function (let's face it, any tests he may have done can't be relied on) and check that the RCD is tripped from the new socket (and a few others) and I'll monitor the socket for a while as I don't don't like mysteries like this strange NE voltage.

There's certainly no harm in doing that and, as you imply, it would serve to reassure you. I strongly suspect that you will find nothing 'wrong', and so we will probably have added yet another item to the list of "life's little mysteries"!!

Do let us know if you discover anything interesting (and/or confusing!).

Kind Regards, John

 

[JohnW2]

If the installer had done any tests he would have realised there was a problem …..

If I understand the OP correctly, it now appears that there probably is no 'problem' - so it's far from impossible that the electrician did undertake tests which confirmed that.

 

[Bob556]

So, are you saying that the 'apparent problem has 'gone away'

Well, the problem was that the socket didn't work, not even enough to power a lamp. Now it does. Sooooo, yes, the apparent problem has gone away. Hopefully it'll stay away.

If I understand the OP correctly, it now appears that there probably is no 'problem' - so it's far from impossible that the electrician did undertake tests which confirmed that.

This is true. He may very well have done everything correctly. I find out that the wires weren't connected by looking at them and tugging them. In fact, the terminal screws weren't actually tight so it's difficult to believe he did check the fundamentals like that. He may well have done electrical tests and may actually have got acceptable results and when I came home something had changed (maybe vibration) so that the conductors were just resting on the edge of the terminal. Who knows?

As you say, we'll probably never know what went on, other than the fact that the socket didn't work, but does now.

I'll leave it a few more days before I fill in the holes in the plasterboard (where he ran the cable). I'm a bit superstitious like that.

 

[JohnW2]

Well, the problem was that the socket didn't work, not even enough to power a lamp. Now it does. Sooooo, yes, the apparent problem has gone away. Hopefully it'll stay away.

Well, yes, you fixed he primary problem (that the socket didn't work) by tightening the terminal screws. However, I was talking about the 'secondary problem', of the apparent 40-45V N-E voltage - but, as I understand it, that's also 'gone away' now?

This is true. He may very well have done everything correctly. I find out that the wires weren't connected by looking at them and tugging them. In fact, the terminal screws weren't actually tight so it's difficult to believe he did check the fundamentals like that. .... He may well have done electrical tests and may actually have got acceptable results and when I came home something had changed (maybe vibration) so that the conductors were just resting on the edge of the terminal. Who knows?

As you say, he cannot possibly have done everything 'correctly', if he left the terminal screws loose - but, as you also say, he may have 'tested' and got satisfactory results (and also found that the socket was ';talking') if he undertook those tests at a point in time when, 'by chance', the loose connections were 'connecting well enough' to give satisfactory results.

However, my point that a certificate probably wouldn't have helped you remains. Regardless of how daft and/or incompetent a person may be, I can't believe that they would issue a certificate indicating that they had undertaken inspection and testing which had 'revealed problems', but not done anything about those problems!

As you say, we'll probably never know what went on, other than the fact that the socket didn't work, but does now.

Frustrating and intellectually unsatisfying though it may be, I suspect that is correct - and it's not all that unusual a situation - life does involve quite a few 'never explained mysteries'

I'll leave it a few more days before I fill in the holes in the plasterboard (where he ran the cable). I'm a bit superstitious like that.

I would be more inclined to describe that as 'being sensible', rather than 'superstitious'. I would certainly do the same!

Kind Regards, John

 

[Bob556]

Hello again, I thought I'd give you an update. Immediately after my last post, I went and bought a socket tester - continuity and RCD. I couldn't wait to use it and tested every socket in the house for polarity and continuity. Every one, including the new socket passed. I had to wait until my wife stopped work before testing the RCD function, but again the new socket passed.

Later that night, I measured the voltage at the new socket. I got between 241-242V L-N & L-E and zero N-E. I took 3 or 4 readings and each time got the above readings. I repeated it 10 minutes later and got 243 V and again, zero N-E.

I've used the socket a few times since then (wouldn't use it until I'd tested) without incident so I'm confident everything is OK.

Now, when the electrician broke his third, or maybe 4th appointment to come look at it, I contacted my bank to claim my money back through VISA. I didn't really expect much tbh, after all, its my word against his and the bank don't know who is right. However, about a week or so ago, on his return from holiday , the electrician phoned me. He said he'd been contacted by the bank, and then said, in rather an unpleasant tone, "what's your problem? " Taking a deep breath, I said that originally I thought the problem was that a mistake had been made in the wiring, but now, perhaps the problem was the attitude of the guy who did the wiring. I told him that the socket didn't work when I came home from work. He said that it did work , he tested it and showed my wife. He did show my wife something and she took his word for it that the lights meant everything was OK.

I said he could not have tested the RCD trip, because my wife was working from home and her PC would have gone off, as would the clock on the oven, and the microwave. He would have needed to go in the garage to reset the CU, and my wife only let him in once at the beginning to turn off the circuit, and at the end to turn on. She didn't leave him alone and made sure the garage was locked after each time. (I only realised that any testing was incomplete when I tested the RCD function as I had to go reset the CU.)

He said he was sick of scammers (!). They were always trying to find a way not to pay and I'd waited long enough to contact him. After another deep breath (I couldn't believe the stuff he was coming out with) I told him that when I got home from work that day, my neighbour was mowing his lawn at the front. I passed the time of day and said I was going to mow my back lawn using my new socket. My mower didn't work. I went and asked my neighbour if I could test the socket with his mower. That didn't work either. I plugged each mower into an extension lead and they both worked. I left him a voice message straight away and still had a record of the call on my phone. (I later tested the socket with a lamp as I said above).

I pointed out that we'd exchanged a few text messages about it, which he had no recollection of, until I read them. In those messages was confirmation of the several dates/times for him to come back. Again, he had no knowledge of them and he wasn't giving a refund because there was nothing wrong when he left. I said that it wasn't unreasonable to expect his 'good work' to function for more than 4 hours from when he left to I came home. In the end, I explained to him that it really came down to which of us put forward the most convincing version of events. His was that I was a scammer trying to get money back despite his work being good, or mine that there was no evidence that the socket ever worked (my wife had no clue what she was shown and took his word), several hours after he left, the socket didn't work, as witnessed by my neighbour who has no vested interest, and critically, he broke several appointments to come back (without explanation) causing me inconvenience. When I tested the socket, I got strange voltage readings and found that the conductors weren't actually connected to the terminals and the terminals screws weren't tight. He had not issued a certificate of work, and it was impossible for him to have tested the work to the required standard as he did not have access to the CU to restore power after the RCD test. If I was a scammer I wouldn't have waited for him to break several appointments over 3-4 weeks before trying to get a refund. Then I asked him, if he was a judge, which version would he believe, mine, with a neighbour to confirm the socket didn't work and a wife to confirm she did not let him back in the garage and the power was never interrupted, or his version that had nothing to support it.

He thought for a minute and then said he was willing to do a deal to avoid any more hassle. He initially offered 10% off but I think my laughter told him what I thought. I pointed out that I'd had a lot of inconvenience, I was out of pocket for the socket tester, had a round trip of nearly 30 miles to get it and lost the time to do so, and spent several hours fixing his work. He laughed and said "several hours? It didn't take me that long to do the whole job". That might be true I said, but I didn't have full use of my hand, but when I left it, the socket worked and continued to work even now

Eventually, he agreed to refund his labour, and to give me a discount on the hardware. He confirmed it in a text whilst we were speaking and I got the money a few days later. I've just remembered, I never did get that bloody certificate lol.

Anyway, job done. To give him the benefit of the doubt, maybe it was bad luck the socket didn't work (although he couldn't have tested it properly) but if his customer service skills were better /he cared more about his work, he would have made a profit on the job. Maybe he'll learn maybe not.

I'd thought I'd update things and I guess a few of you will have a laugh about his attitude.