RCBO tripping next door RCBO

[rustynails]

Testing an RCD on one rfc upstairs tripped the upstairs and downstairs circuis, which was the RCBO next door to it. Turned off the power to all circuits tested downstairs RCBO on its own RCD failed 1x and 5x tests. Disconnected conductors from this RCBO tested RCD at the board worked ok. Put cables back in failed RCD tests. Removed every fuse from every fuse spur and disconnected all plugs etc. Tested ok. Put all the fuses back and all plugs switched on tested again all ok. went upstairs tested rcbo tripped individually. madness ?

 

[Dave OCD]

Sounds like a N-E fault- somewhere.

 

[HappyHippyDad]

This same thing happened to me a few weeks ago. It was very confusing. I went home, came back the next day refreshed and figured it out.

Have you done any IR tests? You need to see if one (or more) circuits have IR faults. My RCD would not trip when tested with the conductors all in place but when I disconnected them the RCD tripped as it should when tested, therefore you know there is no fault with the RCD. Two of the circuits tested as 0Mohms N-E. I found the fault(s) reconnected everything and the RCD passed the tests.

For some reason, on rare occasions, a N-E IR fault can actually stop the RCD from working. I don't know why.

 

[westward10]

If you have a neutral to earth fault of there is no guarantee this will cause an imbalance because the current may still predominantly pass back through the neutral as opposed to earth hence the rcd may not trip. TT systems are prone to this due to the higher impedance of the earth path so the neutral just chooses not to divert that way.

 

[HappyHippyDad]

If you have a neutral to earth fault of there is no guarantee this will cause an imbalance because the current may still predominantly pass back through the neutral as opposed to earth hence the rcd may not trip. TT systems are prone to this due to the higher impedance of the earth path so the neutral just chooses not to divert that way.

But that would not explain why the RCD is not tripping when tested?

 

[westward10]

I believe a neutral to earth fault can desensitive the device by putting a load to the current transformer which effectively raises the trip sensitivity.

 

[PEG]

I think the OP needs to decide,if he is wanting to test the RCD's or the RCD's and their associated circuits.

 

[Richard Burns]

Just thinking about some possible scenarios, not with any valid basis behind them, but if the resistances of a particular fault are just right then it could be possible to get similar, but perhaps not the same, effects as described in the OP. Though it is just off the cuff thoughts.

 

[dmxtothemax]

You most likely have a poor neutral somewhere, so some of that neutral current is finding another path via the earthing system.
you need an electrician to check the neutrals and earths.One is sure to be dodgy.

 

[Wilko]

Just thinking about some possible scenarios, not with any valid basis behind them, but if the resistances of a particular fault are just right then it could be possible to get similar, but perhaps not the same, effects as described in the OP. Though it is just off the cuff thoughts.
View attachment 48134

Always a joy to behold your drawings RB !
Yes, IR testing should reveal a N-E problem and that will likely be the cause of the tripping.

 

[rustynails]

Just thinking about some possible scenarios, not with any valid basis behind them, but if the resistances of a particular fault are just right then it could be possible to get similar, but perhaps not the same, effects as described in the OP. Though it is just off the cuff thoughts.
View attachment 48134

Your diagram to the right is what happened. Great diagram.

Perhaps I need to do some more IR testing N-E it could be an appliance perhaps...

 

[Automation ATO]

Check the zero line, first try to remove the zero line, it is impossible to jump to the zero line and other circuits.

 

[Norah Nabino]

This same thing happened to me a few weeks ago. It was very confusing. I went home, came back the next day refreshed and figured it out.

Have you done any IR tests? You need to see if one (or more) circuits have IR faults. My RCD would not trip when tested with the conductors all in place but when I disconnected them the RCD tripped as it should when tested, therefore you know there is no fault with the RCD. Two of the circuits tested as 0Mohms N-E. I found the fault(s) reconnected everything and the RCD passed the tests.

For some reason, on rare occasions, a N-E IR fault can actually stop the RCD from working. I don't know why.

The RCD operates if there is an imbalance in the voltages coming in on the live conductor and going out on the neutral conductor.So if there is N-E fault implies that some of the voltage from the neutral conductor is diverted to the earth conductor and the RCD will sense that imbalance and trip.

 

[rustynails]

imbalance in the voltages coming in .

I think it's current.

 

[chrisdungan]

forgive me for sounding dense. I'm from the southern hemisphere but I've worked in the UK.
You have 2 rings, 1 upstairs and one down stairs?
in theory no problem. so long as the 2 rings are guaranteed separate and each ring has no crossed over phases and neutrals.
If there are neutrals or phases somehow getting connected into the other ring = problem
crossover round the ring somewhere = problem
neutral or phase from totally another circuit = problem
an unterminated spur = problem

Are all your earths in the right places?
an RCD will trip when the phase and neutral currents are not in balance. Is there a return path through an earth somewhere

 

[tudore]

Testing an RCD on one rfc upstairs tripped the upstairs and downstairs circuis, which was the RCBO next door to it. Turned off the power to all circuits tested downstairs RCBO on its own RCD failed 1x and 5x tests. Disconnected conductors from this RCBO tested RCD at the board worked ok. Put cables back in failed RCD tests. Removed every fuse from every fuse spur and disconnected all plugs etc. Tested ok. Put all the fuses back and all plugs switched on tested again all ok. went upstairs tested rcbo tripped individually. madness ?

A common problem when installing RCBOs where previously there were only RCDs is "borrowed" or common neutrals. I would suggest checking for continuity of neutrals in different circuits, after disconnecting from DB.