Disconnected Neutal Still Showing Connection To Neutral (somewhere)

[J.A.J.]

hi i am replacing a consumer unit over and came across a strange problem with the neutrals when i isolated the old consumer unit. When isolated from supply im still getting 240v between incoming live and out going neutral. I have disconnected all neutrals from block (which clears it from outgoing at main switch) but all circuit neutrals now show still connected to neutral (somewhere). I was thinking it was the obvious old hookey supply, live chopped away but neutral still connected,but it still dosent make sense. Hope someone here can shed a little light on the subject please. Thanks in advance J.A.J

 

[J.A.J.]

Is the supply PME by any chance , this situation is something I experienced working for a DNO , where a reverse polarity or broken neutral even externally in an underground joint meant that the neutral became live and returned a live supply via the earth and bonding connections from neighbouring properties .....

No the neutrals not broken coming in as there isn't a voltage on it across earth

 

[J.A.J.]

Is the supply PME by any chance , this situation is something I experienced working for a DNO , where a reverse polarity or broken neutral even externally in an underground joint meant that the neutral became live and returned a live supply via the earth and bonding connections from neighbouring properties .....

No the neutrals not broken coming in as there isn't a voltage on it across earth

Ditto same for me, rewire on a TN-S. Found fault N-E on a radial, thought put that to one side while I connect the rest up, except I mixed up the faulty one with another and connected it up. All went well until went to test RCD, which timed out. Test button didn't work either. Took a while before I realised mistake.

Tested RCD tested within time and test buttons operate as ment to

 

[R G]

RG gets my ho-lee-cr@p award for the day with that gem.

And how do you know that , I am simply trying to understand what the op has written , and he's now given more info and not PME , the response I have given is based on an actual situation i have experienced before ....

 

[J.A.J.]

I'm led to believe, if you think of how an RCD works, imbalance between live & neutral, with an earth neutral fault, the fault current in the earth can flow back through the neutral, negating any trip. That's how it was explained to me. But being not expert on the technical bit, however I've had that happen to me.

Yeh I understand that ,but if the neutral conductor for said circuits are connected to neutral bar then shouldn't it still trip

 

[Wilko]

And how do you know that , I am simply trying to understand what the op has written , and he's now given more info and not PME , the response I have given is based on an actual situation i have experienced before ....

Hi RG, apologies I seem to have said this the wrong way. What I meant was I believe you and I find it quite scary to that it could happen like that. Cheers, David.

 

[David M]

If there is a current less than 30mA on more than 1 circuit wouldn't this trip the rcd

Only if the total leakage current reaches 30mA. I did a ramp test on an intermittent trip situation once. The RCD tripped @ 10mA even after we had disconnected all accessories (or so we thought) then we discovered a fused spur feeding an outside light. We disconnected that and tested again, this time it ramped to around 15mA then tripped again. After much searching we found an extension lead plugged in but nothing plugged in that. After unplugging it the rcd ramped up to 30mA no problem. Turns out that the extension lead had a N-E fault.

 

[David M]

Yeh I have done IR , low readings on some circuits 7.2meg ,5.3meg lowest was 2.5meg

So these are the lowest readings found between N & E on the total installation?

 

[David M]

Have you tested between Incoming live and each individual out going disconnected neutral per circuit?
Surely its just a process of elimination until you find the culprit?

 

[J.A.J.]

I'm led to believe, if you think of how an RCD works, imbalance between live & neutral, with an earth neutral fault, the fault current in the earth can flow back through the neutral, negating any trip. That's how it was explained to me. But being not expert on the technical bit, however I've had that happen to me.

Yeh I understand that ,but if the neutral conductor for said circuits are connected to neutral bar then shouldn't it still trip

Have you tested between Incoming live and each individual out going disconnected neutral per circuit?
Surely its just a process of elimination until you find the culprit?

Hi David , I had all circuits disconnected and it cleared it from the neutral bar but all neutral conductors showed a circuit. That's what's doing my head in is that it's not just 1 circuit that seems to be the problem (as yet discovered)

 

[David M]

Yeh I understand that ,but if the neutral conductor for said circuits are connected to neutral bar then shouldn't it still trip

Hi David , I had all circuits disconnected and it cleared it from the neutral bar but all neutral conductors showed a circuit. That's what's doing my head in is that it's not just 1 circuit that seems to be the problem (as yet discovered)

Right, I'm getting a picture of what you are getting at now, thanks.
So there is either a path to another incoming neutral, or a N-E fault that was not sufficient to trip the original rcd (assuming this was working correctly)?
One other thing that might seem like a daft question, but, have you tried another voltage tester?

 

[J.A.J.]

Right, I'm getting a picture of what you are getting at now, thanks.
So there is either a path to another incoming neutral, or a N-E fault that was not sufficient to trip the original rcd (assuming this was working correctly)?
One other thing that might seem like a daft question, but, have you tried another voltage tester?

yeh ive tried my old digital test lamps ,my new digital test lamps and my megger MFT all show voltage. Most circuits show 240+, think 1 shows 168v

 

[Lucien Nunes]

As I've said a dozen times before, the voltage reading to something that is supposed to be disconnected (the outgoing N) is meaningless. All it tells you is how the leakage impedance (IR in parallel with stray capacitive reactance) compares to the input resistance of your meter. I don't know what you're trying to achieve by testing voltage to disconnected circuits but it's not technically valid, you should use an alternative test such as IR to prove/disprove any suspicions about these circuits.

 

[J.A.J.]

As I've said a dozen times before, the voltage reading to something that is supposed to be disconnected (the outgoing N) is meaningless. All it tells you is how the leakage impedance (IR in parallel with stray capacitive reactance) compares to the input resistance of your meter. I don't know what you're trying to achieve by testing voltage to disconnected circuits but it's not technically valid, you should use an alternative test such as IR to prove/disprove any suspicions about these circuits.

im not trying to prove any voltage reading on the disconnected conductors, but trying to establish why so many of the circuits are showing a fault and not tripping the rcd , and if without being able to trace it. so correct me then if im wrong, but if the fault current is below 30mA then it wont trip the rcd (as pointed out earlier) and therefore below the safe fault current then it wont be a problem

 

[Lucien Nunes]

What fault exactly are these circuits showing, sorry I might have missed something...

 

[J.A.J.]

What fault exactly are these circuits showing, sorry I might have missed something...[/Q
i am getting low readings neutral to earth on circuits ,but doesnt trip rcd . I understand your last comment im only pointing out that i have a circuit when tested (not looking for v readings, only mention them as to give a better picture (obviously not)). So as i last commented on that, if its below the safe fault current and not tripping rcd then there is no problem.