RCBO Tripping on Sockets circuit when Down stairs lights are switched on

[ionelec1967]

Hi hope somebody out there can help me on this one ,

Problem


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Recently i installed 3 downstairs rooms with downlights, not had any problems when installed.



When the downstairs lights are switched on the socket RCBO ois tripped at the fusebox , the lights stay on plus the RCBO for the downstairs light stays on dosen't trip and you can turn them on and off at the switches.
Tried disconecting room by room but dosent stop the sockets from tripping there is only one ring circuit for the house.
any ideas ....

 

[Hawkmoon]

This is a weird one - can't be a borrowed neutral or surely both RCBOs would trip

Darkwood - are you talking about cables from different circuits being crushed together? If so, surely again both would trip.

 

[ionelec1967]

Cheers for your help on this one i appreciate it when the lights are on and the socket RCBO trips depending on which way the 2 way switch is the socket RCBO will reset with out tripping looking more towards a swich wire fault

 

[Hawkmoon]

A switch wire fault still does not explain the interconnection.

I would fully test both RCBOs first to eliminate them from the hunt and, as previously said, carry out full test procedure on the circuits.

 

[ionelec1967]

Swapped RCBO over just in case still tripping out , agree keeping test sequence methodical is a must will keep you posted will sleep on it

 

[ionelec1967]

True my thinking is a short between lighting circuit and power circuit

 

[Darkwood]

This is a weird one - can't be a borrowed neutral or surely both RCBOs would trip

Darkwood - are you talking about cables from different circuits being crushed together? If so, surely again both would trip.

Tripping is relative to background leakage existing, leakage and mA rating of RCBO ..we can assume 30mA both devices but the one that trips first may have a higher background leakage on the circuit already to get 2 RCBO's to trip together is a massive coincidence when its just leakage concerned because both circuits would have to have the same background leakage and the RCBO control circuits would have to react within the same hundredth of a second... short circuit yes maybe with magnetic shock but leakage i doubt you'll get both tripping and will favour the one already closer to its threshold.

 

[Hawkmoon]

Tripping is relative to background leakage existing, leakage and mA rating of RCBO ..we can assume 30mA both devices but the one that trips first may have a higher background leakage on the circuit already to get 2 RCBO's to trip together is a massive coincidence when its just leakage concerned because both circuits would have to have the same background leakage and the RCBO control circuits would have to react within the same hundredth of a second... short circuit yes maybe with magnetic shock but leakage i doubt you'll get both tripping and will favour the one already closer to its threshold.

I see what you're saying there, though I have experienced this dual tripping on occasion with borrowed neutrals - could be a momentum effect even though current is halted by other RCD
But what is strange with this is that presumably some current in the lighting circuit (when switched on) is flowing through the socket's RCBO - yet the lighting RCBO and the switched light stays on

 

[spark 68]

Thought about that one but if shared from the sockets when it trips the RCBO for the sockets the lights still work, the neutral would be took out

On most Domestic (nearly all) RCBOs the N is not switched, ie. they are usually single pole, so even though one has already tripped the N is still connected.

 

[Hawkmoon]

On most Domestic (nearly all) RCBOs the N is not switched, ie. they are usually single pole, so even though one has already tripped the N is still connected.

Perhaps a bit ignorant on my part but I did not realise this (thought they were all dp) - that means then that this type of device will not then isolate a neutral to earth fault?

 

[spark 68]

Perhaps a bit ignorant on my part but I did not realise this (thought they were all dp) - that means then that this type of device will not then isolate a neutral to earth fault?

Yep,

But usually as you say it knocks the two out, because you still have an imbalance via the L on the working one and the N on the tripped one, I have seen this more on the old 16th Boards with RCBOs on the sockets and none on the lights.

Edit: The RCDs (80 Amp etc.) in dual boards are DP

 

[Hawkmoon]

Yep,

But usually as you say it knocks the two out, because you still have an imbalance via the L on the working one and the N on the tripped one, I have seen this more on the old 16th Boards with RCBOs on the sockets and none on the lights.

Edit: The RCDs (80 Amp etc.) in dual boards are DP

Yes, I knew that - that's what made me assume that RCBOs were the same (thought that was what the extra height was all about)

Every day a school day lol

 

[spark 68]

Bell one out Hawk if you get a chance (RCBO), the Wylex ones usually have a diagram on the side.

 

[Octopus]

Wonder if he's tested for a borrowed neutral, seeing as its the hall/landing area that causes the trip?