RCBO tripping light circuit

[redtop]

So last night the downstairs RCBO 6a light tripped, and tripped straight away with all light switches off this morning. I have gone round and checked every light switch, and also outside lights noting I have looped at the switch not the pendant. I found one loose neutral which was on the 4way light switch in the kitchen. Sorted that and RCBO isn't tripping, could that have been the fault or should I expect it to trip again soon....

[TonyT]

Sounds like the problem is solved..

[PeterW]

Internal and external lights on the same RCBO ..? Will probably end up with some nuisance trips then as external bulbs going are more common than internal. 

[redtop]

1 hour ago, PeterW said:

Internal and external lights on the same RCBO ..? Will probably end up with some nuisance trips then as external bulbs going are more common than internal. 

Exactly what I thought, plus driving rain causing issues. But no damp when opened up and no bulbs blown, plus it still tripped with all lights off. Only thing I found was a loose neutral on an internal switch, which I have fixed and it hasn't tripped since. Just little suprised that caused the rcbo to trip in the first place.

[ProDave]

Metal back boxes?  Loose neutral touching the back box would trip an RCD. 

 

Otherwise likely a pinched wire, and by removing and re fitting all the switches you have unpinched it.

[Ajn]

1 hour ago, redtop said:

Just little suprised that caused the rcbo to trip in the first place.

The neutral to the circuit is supplied through the RCBO. When the current in the neutral and the live are in balance the RCBO will not trip. If the neutral loses this balance though a loose connection even for a very very short period the RCBO will see this as a fault and trip.

[redtop]

1 hour ago, Ajn said:

The neutral to the circuit is supplied through the RCBO. When the current in the neutral and the live are in balance the RCBO will not trip. If the neutral loses this balance though a loose connection even for a very very short period the RCBO will see this as a fault and trip.

Yep, but why would it do that when every light is turned off so no current is bring drawn. Odd. Perhaps it was touching the back box, but it was the usual 'looks like its in'  but wasn't.

[Marvin]

As @Ajn was pointing out RCBOs are different. And their ability to sense a leakage from the neutral to earth is probably a life saver.

[Radian]

2 hours ago, redtop said:

Yep, but why would it do that when every light is turned off so no current is bring drawn. Odd. Perhaps it was touching the back box, but it was the usual 'looks like its in'  but wasn't.

If the neutral did touch to earth then it stops current in other circuits returning via the same RCBO neutral (which now has earth potential at both sides) causing the imbalance that trips it out. This is how they sense leakages from the neutral to earth as @Marvin describes.