Earth/Neutral fault..Help Needed!!

[dtec dave]

Probably going to get slated for not knowing/doing something wrong but here goes!!

So, been asked to do a board change for a customer, when I turned up they explained that had had a new PME done a few weeks ago, when I mentioned that their house wasn't earthed the customer said that the installers had said it 'wasn't urgent but needed doing at some point' . Anyway I did a quick ZS test on a socket and found I was getting 1.20 ohms..not bad for no earth.

I then proceeded to start dead testing the existing board, upon testing a ring circuit in the house I found that I was getting voltage (190v) between the disconnected neutrals and live. At 1 point I even had the neutral tail disconnected from the meter with the ring neutrals connected on to the neutral block to find all the electrics working in the house!! (To try and explain to the customer what is happening)

Any suggestions on where I begin to start looking for this fault??

Cheers in advance

 

[telectrix]

i'd start by sorting out the earth -- diss. all bonding then once you have a decent earth, proceed logically. ( my grandmother was a Vulcan).

 

[fairlight]

Sort out and verify earthing. Carry out tests on each final circuit in the correct sequence and you will locate the issue. R1+R2.....Ring circuit continuity....Insulation resistance....Zs. Don't be distracted. There is a correct sequence of testing for a reason.

 

[Wilko]

I then proceeded to start dead testing the existing board, upon testing a ring circuit in the house I found that I was getting voltage (190v) between the disconnected neutrals and live.

Hi - this has me confused - are you saying the double pole isolation switch in the board was off and yet you were reading 190V?

 

[dtec dave]

Hi - this has me confused - are you saying the double pole isolation switch in the board was off and yet you were reading 190V?

No, the 2 neutrals of my ring circuit were disconnected and I was reading 190v between each leg and incoming live.
[automerge]1571767195[/automerge]

Hi - this has me confused - are you saying the double pole isolation switch in the board was off and yet you were reading 190V?

...and yes I had it live with the cover off if that's what you are referring to.

 

[PEG]

Hi,why were you measuring between those disconnected neutrals and supply?

 

[Simon47]

No, the 2 neutrals of my ring circuit were disconnected and I was reading 190v between each leg and incoming live.

I'd expect that Were you using a multimeter by any chance ?
There's capacitance between the neutrals and earth, as well as possibly some conductance (inverse or resistance). You've formed a potential divider between L & E with your meter as one leg, and the N-E impedance as the other leg. The voltage (and phase) of the midpoint (the N wires) depends on the ratio of the impedances of your meter and N-E.

 

[PEG]

Hi,could i ask what detailed inspection and testing,was done,regarding the earthing arrangements,at origin?

 

[dtec dave]

Hi,could i ask what detailed inspection and testing,was done,regarding the earthing arrangements,at origin?

I'd expect that Were you using a multimeter by any chance ?
There's capacitance between the neutrals and earth, as well as possibly some conductance (inverse or resistance). You've formed a potential divider between L & E with your meter as one leg, and the N-E impedance as the other leg. The voltage (and phase) of the midpoint (the N wires) depends on the ratio of the impedances of your meter and N-E.

How does this explain disconnecting the neutral tail coming out of the meter and the board still being live across L-N? And no not using multimeter, checked it with both my multifunction tester and voltage testers.

 

[Lucien Nunes]

I don't understand your initial question. You know you've got an N-E fault(s), you demonstrated it to yourself and the customer. You also have suspect earthing conductor connectivity or similar. The two don't sit nicely together - they can make lots of exposed stuff live.

As per Fairlight, start testing from the beginning, systematically, in order. Make no assumptions, take no guesses. When you find the circuit with the N-E fault, check it carefully for thermal damage. Your disconnected neutral tail would have sent the entire load current of the house down it, and if it's a lighting circuit... 1mm isn't really specced for that!