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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 ?
 
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D

Deleted member 26818

Bit confused with the RCD and RCBO references.
Are you saying that there is some circuits covered by an RCD and other circuits on individual RCBOs?
 
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  • #3
Bit confused with the RCD and RCBO references.
Are you saying that there is some circuits covered by an RCD and other circuits on individual RCBOs?
All bo’s ...
 

buzzlightyear

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must be the second person to day working on their next door neighbours house I will go round to mine and see if their having trouble.;)
 

buzzlightyear

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RCBO on its own RCD failed
come again ,take a pic to see what you have got on the c/u.
 
D

Deleted member 105166

topic title somewhat misleading in this context, i.e. "next door"
 

buzzlightyear

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I’m still confused lol once I’d disconnected everything on the circuit the RCBO passed the RCD tests.

Before that it was only passing if I disconnected the conductors from the RCBO.
Before that it was only passing
was it passing when you tested it with out the circuits being on or off .;)
 
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  • #11
topic title somewhat misleading in this context, i.e. "next door"
When I say next door I mean in the box.

was it passing when you tested it with out the circuits being on or off .;)
This occurred when I auto rcd tested upstairs RCBO sockets ‭which was tripping both upstairs and downstairs. The first time I got the Rcbo to pass was when I disconnected all other circuits and disconnected the conductors from the rcbo and rcd tested at the origin.
 

buzzlightyear

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RCBO sockets ‭which was tripping both upstairs and downstairs.
wrong tails in maybe.
 

Rpa07

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Polarity in accessories, did you do an R1R2 and test every point? Not sure if that would cause your issues!
 
Seen some people on here talk about N-E faults causing a RCD to stop operating, never seen it myself but I sure someone else will be able to explain.

Have you tried an insulation resistance test between the two circuits with them disconnected from DB? Perhaps you have a bit of a short between the 2 circuits if they are causing each others RCBO's to operate. Cable burns from installation maybe.
 
"Removed every fuse from every fuse spur and disconnected all plugs etc. Tested ok"
So with all loads removed the circuit tested ok?
Could one of the appliances be leaking DC or not compatible with an AC type RCBO (assuming it is an AC type RCBO)
 

happyhippydad

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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.
 
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

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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?
 
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

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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

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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.
RCBO Trip 5.jpg
 
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

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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.
 
  • Thread Starter Thread Starter
  • #25
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...
 
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.
 
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
 
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.
 
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