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.]

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.

 

[J.A.J.]

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

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.

 

[J.A.J.]

sorry went a bit mad there with posts, got a bit mixed up where to post, it seems a bit all over the place

 

[Lucien Nunes]

But what's the problem? The thread title says 'connection to neutral' but then you say the lowest IR value N-E you're getting is 2.5MΩ which isn't exactly what I'd call a connection. It will give you a voltage reading from line, but it certainly won't trip an RCD. If the neutral is say 5V from earth with the installation loaded, then the maximum leakage that will cause is 5/2,500,000=0.002 mA, or 7,500 times less than the lowest current that should cause a trip (15mA). Even 2.5MΩ L-E will only leak 230/2,500,000=0.09mA. An RCD won't trip until the IR is down to 0.015MΩ.

I can't see anything strange here...

 

[happysteve]

^^^ what he said. I'm also struggling to see what the problem is. Measuring voltage is an unreliable way of determining if there's a fault (unwanted connection) or not, an IR or even continuity test is the way to go. You say "low readings N to E" but the lowest reading you've quoted will never trip an RCD, as Lucien Nunes says (unless there's a genuinely low reading that you haven't quantified?). I'm also confused by, "so many circuits showing a fault" - what (other than misleading voltage readings) do you mean by, "showing a fault?"

 

[J.A.J.]

hi ,thanks for your comments Lucien and happysteve (and everyone else who posted a comment). Im sorry i have worded it wrong by using fault. I have obviously been thinking to much about nothing, it was just something the costumer had said when i first went to his house (4 Months ago) that "a light wouldnt isolate unless you switch incomer off. thinking back cant remember if the mcb had latched on. It only came back into my head when i the light in the porch above my head wouldnt isolate when i switched the mcb off, ironically the new mcb was faulty. Thats why i disconnected the neutrals to see if any had a second connection to a neutral, then everything got lost in translation. Thanks again lucien for explaining ,i

 

[Midwest]

I'm a bit lost with this thread, probably because we've added our little anecdotes.

However the point I, and Telectrix are making is, from experience, a neutral-earth fault can (sometimes)prevent the operation of an RCD. In my instance, it certainly prevented my MFT from carrying out the testing of the RCD and the operation of the 'Test' button on the RCD.

Something to bear in mind, should you come across a similar situation.

 

[LED Lighting]

Hi.
Just reading your very confusing post and I got lost several times.

Would I be right in saying you could not isolate the light in the porch unless you turned off the incomer? So you then had a MAD thought about leaving the incoming live connected and on. But disconnecting the neutral supply cable our of the meter?? And you still had 230v L-N

All I hope is that I am wrong but this is what it sounds like to me

 

[David M]

Hi.
Just reading your very confusing post and I got lost several times.

Would I be right in saying you could not isolate the light in the porch unless you turned off the incomer? So you then had a MAD thought about leaving the incoming live connected and on. But disconnecting the neutral supply cable our of the meter?? And you still had 230v L-N

All I hope is that I am wrong but this is what it sounds like to me

Yes the thread is getting very confusing. The details of what the problem actually is, is vague. The lowest reading for the IR test between N&E is claimed to be 2.5meg which Lucien nicely showed in his post would not be expected to cause a trip fault or indicate a N-E fault. Originally it was claimed that all the outgoing circuits produced a voltage of 240 + between incoming live and each out going N although each N was disconnected from anything. This seems very strange and doubtful. Again Lucien nicely explains about "stray capacitive reactance", showing why a voltage test to determine a fault in this situation is not valid and pointless, and you'd also expect different voltage readings between different circuits in this case. Which the oper eventually admits that one circuit reads at 168v.
Regarding the porch light problem, your guess is as good as mine. Again the details are too vague to form any conclusion.

 

[J.A.J.]

I'm a bit lost with this thread, probably because we've added our little anecdotes.

However the point I, and Telectrix are making is, from experience, a neutral-earth fault can (sometimes)prevent the operation of an RCD. In my instance, it certainly prevented my MFT from carrying out the testing of the RCD and the operation of the 'Test' button on the RCD.

Something to bear in mind, should you come across a similar situation.

Thanks

 

[J.A.J.]

Yes the thread is getting very confusing. The details of what the problem actually is, is vague. The lowest reading for the IR test between N&E is claimed to be 2.5meg which Lucien nicely showed in his post would not be expected to cause a trip fault or indicate a N-E fault. Originally it was claimed that all the outgoing circuits produced a voltage of 240 + between incoming live and each out going N although each N was disconnected from anything. This seems very strange and doubtful. Again Lucien nicely explains about "stray capacitive reactance", showing why a voltage test to determine a fault in this situation is not valid and pointless, and you'd also expect different voltage readings between different circuits in this case. Which the oper eventually admits that one circuit reads at 168v.
Regarding the porch light problem, your guess is as good as mine. Again the details are too vague to form any conclusion.

Thanks

 

[J.A.J.]

Hi.
Just reading your very confusing post and I got lost several times.

Would I be right in saying you could not isolate the light in the porch unless you turned off the incomer? So you then had a MAD thought about leaving the incoming live connected and on. But disconnecting the neutral supply cable our of the meter?? And you still had 230v L-N

All I hope is that I am wrong but this is what it sounds like to me

No ,main swith and mcbs OFF

 

[Midwest]

OP, I think if you still want help from the learned members on this forum (I exclude myself from that list), it would probably be best that you start your thread from the beginning again; using terms we can all understand, highlighting the installation you found, what you were intending to do, the faults you encountered and the test equipment you have at your disposal.

I think we are all struggling to understand the issues you have, mainly from the terms you are using, and the 'tests' you are conducting. It may be we are just confusing ourselves, but clarification might help?

 

[westward10]

OP, I think if you still want help from the learned members on this forum (I exclude myself from that list), it would probably be best that you start your thread from the beginning again; using terms we can all understand, highlighting the installation you found, what you were intending to do, the faults you encountered and the test equipment you have at your disposal.

I think we are all struggling to understand the issues you have, mainly from the terms you are using, and the 'tests' you are conducting. It may be we are just confusing ourselves, but clarification might help?

I was about to post the same.

 

[Lucien Nunes]

I think I got it: There was a faulty MCB which did not open when operated manually*, causing the porch light circuit to stay on unexpectedly. This, and a remembered similar observation by the homeowner, created a suspicion that some false connection existed bypassing something in the CU.

Various tests were undertaken involving the supply which naturally was still live, so live tests were used instead of dead. During these experiments, an erroneous assumption was made about the significance of the voltage reading to a disconnected conductor, which along with low but not significant IR readings added to the suspicion, which was the subject of the thread.

Along the thread, the apparently innocent RCD was dragged in as another suspect as it had not tripped while the suspected fault existed. In fact there was no reason for it to do so but this was not realised due to not having calculated I=V/R.

Am I close?

* This is unusual and nasty. I would like to know more about this aspect.