20 Volt oddity at recent rewire

[M-B-Electrical-Services]

Hi all,

I have an unusual issue with a recent rewire I have just completed which I hope you guys can assist with.
For background, this is a complete strip out and rewire of a domestic property (bungalow) with an unusual but appropriate reference method.
For this rewire, due to the fact that it is a bungalow with easy loft access and zero insulation installed, I opted for reference method E (perforated tray) with a mix of Klik roses and Klik lighting distribution units used for the lighting which has worked extremely well in this case as the homeowner wanted to maximise loft space which we have certainly achieved here.
Anyway, the issue I am having is on one of the lighting circuits where I am getting 20v between N-CPC - N-SwL - Swl - CPC when the switch is in the open position.

All voltages between L - N, L - CPC, N - CPC are correct when the switch is in the closed position.
To me, this indicates either a loose connection or high resistive joint but I have checked everything and all appears in good order.
I have turned all circuits off except the offending circuit with no effect.
Due to the reference method used, I can see all conductors and can trace them for damage easily and all wiring within the walls is contained within oval trunking with no pictures hung within the prescribed zones.

Have I missed something obvious here? I have my NICEIC assessment coming up soon and wold like to use this property for assessment purposes but until this unusual fault is found, I obviously cannot do that.

Mike

 

[M-B-Electrical-Services]

I don’t think it’s a problem at all , as stated already it’s most likely caused by capacitance or inductance . You have already proved its not resistive .
its not a test listed in GN3 or BS7671 .
if it passes all other relevant test its fine.
try loading the circuit down with a lamp and lamp holder and i think the voltage will disappear .
meters generally measure volts in a high impedance mode (in the megohms) once any real current is drawn from the circuit the voltage should drop a great deal

I have come to the same conclusion after exhausting all other avenues.
I have my NICEIC inspection coming up in the next 2 weeks and will be using this property as one of my examples which is why I have gone a bit overboard on it.
All I have really achieved is plenty of wasted time and lots of frustration.
Luckily, the client is a friend so they weren't too put out by my being there.

I'll take this one on the chin and chalk it up to experience (or lack of in this case) and know that in future, unless there is clearly a broken conductor, I will be familiar with this scenario and know how to deal with it.

Thanks for the input!

 

[M-B-Electrical-Services]

Agree with the above, probably a coupled/induced voltage.

What results did you get when you tried measuring the same voltage, but with a low impedance meter, or with a very small load connected?

There was no difference whatsoever in this case bud.

 

[DPG]

There was no difference whatsoever in this case bud.

That's more interesting then. I'm surprised at that.

 

[M-B-Electrical-Services]

That's more interesting then. I'm surprised at that.

Something you may find interesting is that, sporadically, my meter would jump to a DC voltage and show a negative result of around minus 35v just for the slightest of seconds then go back to it's original 49v.

At this point my head fell off!

Although I have 25 years in the game, this one has truly stumped me and, although I now know the cause, it still has given me much to think about!!

 

[M-B-Electrical-Services]

My MFT has just been calibrated before anyone asks