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!

 

[Cid]

Probably a shared neutral somwhere. Neighbor?

Is it a converted flat?

 

[PEG]

Hi,i'll be honest,if i was attempting to explain a situation to a customer,in a property with a suspected earth issue,disconnecting the neutral tail,and leaving the line connected,would not be a method i would choose.

This is a situation,which would be considered dangerous,in an older property,where earths at origin,may be poor,and an original fused neutral,had blown.

 

[dtec dave]

Hi,i'll be honest,if i was attempting to explain a situation to a customer,in a property with a suspected earth issue,disconnecting the neutral tail,and leaving the line connected,would not be a method i would choose.

This is a situation,which would be considered dangerous,in an older property,where earths at origin,may be poor,and an original fused neutral,had blown.

Any good advice to give, you have taken the time to post 3 times on this topic but every post is irrelevant to the question I asked?

 

[Deleted account]

Any good advice to give, you have taken the time to post 3 times on this topic but every post is irrelevant to the question I asked?

I too do not like irrelevant or negative coments when asking a legitimate question, but I think you need to re read pegs posts as they are relevant and I couldn’t detect any negativity other than stating concern over a potentially dangerous issue.

In the past we have had on this forum, if you don’t know you shouldn’t be doing it. It’s changed.

all the posts have been in order to help. Re read them.

 

[snowhead]

I think all 3 of PEG's posts are relevant.
Re PEGs last post, it's covered by the very first line of your O.P

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

Then you mention Dead testing but as you have 170v it's not dead.

 

[westward10]

Have you actually verified Ze as suggested in #2. A random test at a socket will prove nothing.

 

[davesparks]

Any good advice to give, you have taken the time to post 3 times on this topic but every post is irrelevant to the question I asked?

The best advice I'd give to start with is that you stop creating dangerous situations by disconnecting the neutral of a live installation.
As lucian has pointed out this will have diverted the load current via the fault to earth and potentially caused a lot of damage in doing so, not to mention the significant danger to your life and that of anyone else in the property.

 

[Simon47]

How does this explain disconnecting the neutral tail coming out of the meter and the board still being live across L-N?

Oh dear. You need to read it again.
You've made no mention of isolating the incoming L so we have to assume that's at around 240V relative to earth and incoming N.
You've disconnected the N.
You measure between the 240V L and something that is now "sort of floating" with various resistive and capacitative paths (one of which is your meter) to both L and E.
So the N will be at some voltage between E and L - and you are measuring the difference between that and L.

 

[Cid]

This thread is making my head hurt. I've read it start to finish and back to front. Still can't work out what the heck is going on

 

[PEG]

Hi dude,i apologise if i have offended you,but your original post title,was regarding the earthing. You were asked several times,including by myself,regarding this,and got no answer.

I am sorry you think my points regarding the safety aspect of disconnecting and then demonstrating,are irrelevant....this is a worry.

I wish you well and success in your quest,but as the great Deborah Meaden said....i'm out?