Disconnected Neutal Still Showing Connection To Neutral (somewhere)

[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?