Voltage reading puzzle

[toast]

230V single phase supply.
6amp Lighting circuit, T&E 1.0/1.0
Readings
Highest r1+r2=1.72
IR: L-N, L-E, N-E all >299 Mohms
But when energised there is voltage reading across the conductors at the board as follows:
N-E 112V
L-N 107V
L-E 107V
Then at the light fittings:
N-E 127V
L-N 240V (closed circuit)
L-E 7V

The voltage readigns were taken with Line and neutral terminated at MCB and neutral bar respectively but with CPC/Earth not connected at Earth bar.
The circuit does not trip when energised.
Any thoughts of why this is occurring?

 

[SirKit Breaker]

Firstly why did you test the voltage with the CPC disconnected?
Secondly, think about what you havent done, and why you are experiencing the problems that you are.
Thirdly think about what you have done again, and why this might stop the circuit from tripping if there is an earth fault!

You should be able to answer your own questions if you think about it.

Cheers..........Howard

 

[trev]

A voltage L-E when E isn't connected to anything??

 

[ste77]

Is this a wind-up? Especially since its called a "puzzle".

 

[Octopus]

Puzzle my foot. Readings like that mean no earth or no neutral.

 

[toast]

There had been a unit swap (not by me) and the installer called me as they had got a belt of the CPC. that is why I tested as I did.
I can only think that it is a polarity problem as I get continuity with earth and IR readings are really good.
But I tested all Perm lives at fittings, so if it polarity must be connected incorrectly within voids or walls.

All other circuits test off fine.

I know without earth connected there will be no earth fault.

 

[ste77]

where did he get a belt off the cpc? consumer unit end or at the light? if hes changed the CU and the lighting circuit worked fine previously then its something hes done, maybe nicked a cable when screwing the CU up?

 

[toast]

Con unit
I was informed reason for unit change was that there had been fusing issues. But the information I have received regarding this, so far is vague.
But if cable nicked, I would expect IR issues!

 

[ste77]

so he had the power on and the cpc disconnected??? why????

 

[toast]

so he had the power on and the cpc disconnected??? why????

TBH I don't know why, just told me he did.
I wouldn't expect to get a belt though regardless, of this!

 

[ste77]

he sounds like he doesnt have a clue. id be checking everything again, if hes stupid enough to do that god knows what else hes done.

 

[plugsandsparks]

so he had the power on and the cpc disconnected??? why????

Sounds scary, .....

 

[toast]

May sound scary but I wasn't there at the time. So don't know the reason behind this, just know that he got a belt, which then led me to testing as I did.

 

[ste77]

Sounds scary, .....

lucky guy considering the fault, nice that he left the job for someone else though......

 

[toast]

he sounds like he doesnt have a clue. id be checking everything again, if hes stupid enough to do that god knows what else hes done.

Well that is a fair assumption, I did disconnect all the circuits and reinstalled, without the aid of any pre-planned EIRC and a young family with pregnant mother complaining about the heating and Jeremy Kyle being off.
All other circuits tested off fine.
This is genuinely not a wind up.

 

[ste77]

is it loop in?

 

[toast]

is it loop in?

It's mixed bag some fittings are looped-in at ceiling and others are junction/jointed in void.

 

[ste77]

It's mixed bag some fittings are looped-in at ceiling and others are junction/jointed in void.

id be trying to break the circuit down and find what leg your fault is on.

 

[Octopus]

id be trying to break the circuit down and find what leg your fault is on.

I'd be doing dead tests at different fittings!

 

[toast]

id be trying to break the circuit down and find what leg your fault is on.

That is my next move, just a little puzzled why this fault could occur. Never come across it before.

 

[ste77]

That is my next move, just a little puzzled why this fault could occur. Never come across it before.

i always enjoy stuff like this, gives you a greater sense of satisfaction when i find the fault, unfortunately with our line of work these things occasionally crop up.

 

[toast]

I'd be doing dead tests at different fittings!

The circuit is on two levels, my thought were to disconnect the supply that enters the loft. Then test the level below, hopefully eliminating one floor.
Hoping that the fault lies within the loft as access is easier.

 

[ste77]

I'd be doing dead tests at different fittings!

Hes said hes already IR tested and its clear, but im inclined to think id be doing them again!

 

[toast]

i always enjoy stuff like this, gives you a greater sense of satisfaction when i find the fault, unfortunately with our line of work these things occasionally crop up.

Indeed, and once you have diagnosed the fault, it's in your armour.

 

[ste77]

The circuit is on two levels, my thought were to disconnect the supply that enters the loft. Then test the level below, hopefully eliminating one floor.
Hoping that the fault lies within the loft as access is easier.

Only you'll know whats easiest, did the guy only change the CU? wasnt poking around in anything else?

 

[Octopus]

Hes said hes already IR tested and its clear, but im inclined to think id be doing them again!

An IR test on a circuit with a "break" on it or loose connection isn't going to tell you anything, whereas a R1 + R2, R1 + RN, R2 + RN to confirm the continuity of all conductors followed by IR would be of more use.

 

[toast]

Hes said hes already IR tested and its clear, but im inclined to think id be doing them again!

Yes the IRs came up brand new, I did test twice but there were people in the house, may be that a switch could have been opened then closed without my knowledge.

 

[ste77]

An IR test on a circuit with a "break" on it or loose connection isn't going to tell you anything, whereas a R1 + R2, R1 + RN, R2 + RN to confirm the continuity of all conductors followed by IR would be of more use.

.
Yes agreed.

 

[Octopus]

.
Yes agreed.

But I don't think the OP does though. lol

 

[toast]

Only you'll know whats easiest, did the guy only change the CU? wasnt poking around in anything else?

I did ask the question and claims not to have touched anything else, other than the CU. Which also seems to be confirmed by what the occupants are telling me.

 

[ste77]

I did ask the question and claims not to have touched anything else, other than the CU. Which also seems to be confirmed by what the occupants are telling me.

Take onboard murdochs advice and let us know how you get on.

 

[toast]

But I don't think the OP does though. lol

I do agree, I tend to only perform the r1+r2, confirm the switching, then IR it.
But as this is a special occasion, I shall on this occasion be performing additional tests on r1+rN and r2+rN. Before we start breaking parts of the circuit down.

 

[toast]

Take onboard murdochs advice and let us know how you get on.

Duly noted and will report back on my findings.

 

[gaz101]

Have you reconected the cpc at the db

 

[partypest]

Pain, pain & more pain. I had one of these the other day. Eventually traced it to a borrowed neutral AND a pinched cable. The frustrating thing about these faults is they can be so time consuming to find but the only way is to start from the beginning and test from point to point in my experience. A customer told me the other day that a guy from SSE spent three days testing in their house to find a neutral fault. Good luck mate.

 

[Octopus]

I do agree, I tend to only perform the r1+r2, confirm the switching, then IR it.
But as this is a special occasion, I shall on this occasion be performing additional tests on r1+rN and r2+rN. Before we start breaking parts of the circuit down.

Special occassion?? You have voltage readings that suggest a lost neutral or earth, so checking continuity of ALL cores from the board to the accessories is the only step to make, this time, and every time you come across these situations.

 

[toast]

Have you reconected the cpc at the db

No, I disconnected the circuit

 

[toast]

Special occassion??

As this fault is new to me, that is why I asked the original question, it's an historical fault, not something I have introduced and required some help on fault finding and diagnostic. Which I grateful that you have offered.

 

[toast]

Pain, pain & more pain. I had one of these the other day. Eventually traced it to a borrowed neutral AND a pinched cable. The frustrating thing about these faults is they can be so time consuming to find but the only way is to start from the beginning and test from point to point in my experience. A customer told me the other day that a guy from SSE spent three days testing in their house to find a neutral fault. Good luck mate.

Well hopefully experience will put me in a more informed position next time.

 

[toast]

You have voltage readings that suggest a lost neutral or earth, so checking continuity of ALL cores from the board to the accessories is the only step to make, this time, and every time you come across these situations.

As I stated in OP, if I test across switch live and neutral on a closed circuit I get 240V at all fittings, which would suggest that the neutral is present. Unless as mentioned the neutral is borrowed/shared or returning via they earth.
I am unsure what you mean be lost with regards to this.
But I am grateful for your input, is it possible that the fault has been introduced via damage between conductors of two differing circuits and therefore also testing for that,via IR tests across differing circuits.