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