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

 

[LankyWill]

solar panel arrangement in loft?

 

[Richard Burns]

So long as there is any earth reference (or any voltage reference) on the neutral circuit, even fairly slight, then the incoming live (which is still live presumably) at 230V will show that there is 230V between it and the neutral.
It would only be if the entire circuit were totally "floating" that the voltage would not register.

 

[Taylortwocities]

What are you testing this with?

Ps don't forget that neutral is connected to Earth (somewhere) on the supply side.

 

[Midwest]

Have you carried out an IR test on the final circuits?

 

[J.A.J.]

What are you testing this with?

Ps don't forget that neutral is connected to Earth (somewhere) on the supply side.

Hi thanks for the reply , I have the supply end totally disconnected

 

[J.A.J.]

Hi thanks for the reply , I have supply totally disconnect from meter

 

[David M]

Hi thanks for the reply , I have supply totally disconnect from meter

Like Richard said, if there is anything still connected somewhere on the installation and it has some possible earth path via the neutral, then it is possible still show a voltage to live. (obviously discounting a fault, or some unknown factor) If all neutrals are disconnected at both ends and are floating then I would say this indicates an earth/neutral fault on a circuit.

 

[J.A.J.]

If there's an earth/ neutral fault on any of they circuits ,surely it would trip the rcd

 

[Taylortwocities]

If there's an earth/ neutral fault on any of they circuits ,surely it would trip the rcd

He is installing a new CU. maybe the old CU (fuseboard) does not have an RCD> so it won't trip.

As above, needs IR test on the circuits, if there's an E>N fault, somewhere then there may be a path to earth through copper pipes, etc..

 

[David M]

If there's an earth/ neutral fault on any of they circuits ,surely it would trip the rcd

Sorry, with you not mentioning whether or not the existing installation was RCD protected I just assumed that was possibly the reason for the swap of the CCU. Though you may still have a neutral to earth path that doesn't trip the RCD, where any leakage current is less than 30mA.

 

[Wilko]

It's a puzzler, but I'm liking Midwest's thought of an IR problem, otherwise as JAJ says the RCD would have been telling us? Cheers, David.

 

[J.A.J.]

Thanks ,I was upgrading from an older (not ancient CU ) which was a split board,the rcd in the existing board didn't trip of either before I disconnected it

 

[telectrix]

sometimes a N-E fault will stop a RCD from tripping.

 

[J.A.J.]

Have you carried out an IR test on the final circuits?

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

 

[J.A.J.]

sometimes a N-E fault will stop a RCD from tripping.

What do you mean "stop from tripping"

 

[J.A.J.]

Sorry, with you not mentioning whether or not the existing installation was RCD protected I just assumed that was possibly the reason for the swap of the CCU. Though you may still have a neutral to earth path that doesn't trip the RCD, where any leakage current is less than 30mA.

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

 

[Midwest]

What do you mean "stop from tripping"

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.

 

[westward10]

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.

I believe this can happen on TT systems, for example if you have a neutral/earth fault, the current flow will take the path of least resistance and this is likely to be the neutral path and not earth due to the electrode impedance, hence the rcd will not sense an inbalance to make it trip.

 

[DPG]

I still dont get it. A fault current would still cause an imbalance and trip the rcd. Daz

 

[westward10]

I still dont get it. A fault current would still cause an imbalance and trip the rcd. Daz

Not necessarily if the fault decides to use the neutral path because it is the route of least resistance there will be no imbalance.

 

[DPG]

Ah I see what you mean now on a tt system. Mmm need to think about this one! Daz

 

[telectrix]

i've had it on a TN system. even the test buttons on both RCDs failed to operate them

 

[westward10]

i've had it on a TN system. even the test buttons on both RCDs failed to operate them

It isn't impossible on a TN system but it shouldn't stop the test button operating the device.

 

[telectrix]

i know, weird. i was on it for over an hour before finding a radial the used to feed the immersion heater but was dissed at the load end was the cause.

 

[westward10]

i know, weird. i was on it for over an hour before finding a radial the used to feed the immersion heater but was dissed at the load end was the cause.

Must admit have never experienced this just know the supposed theory behind it so I am just guessing with the test button. Weird stuff this lectricity.

 

[Midwest]

i know, weird. i was on it for over an hour before finding a radial the used to feed the immersion heater but was dissed at the load end was the cause.

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.

 

[R G]

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 .....

 

[Wilko]

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

 

[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 .....

Hi ,it's a TNS system ,checked the earth coming of cable head (ze 0.30ohms) no return voltage between incoming neutral and earth. It's an old cast 3 fused cable head which also had me thinking about the neighbour scenario but no other cables are coming of it . Had to put the CU back together as had to leave the job cos the customer was going away this morning

 

[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.

 

[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?"