S
sparkinlee
I did a CU upgrade recently, and had a call back for the lighting rcbo tripping randomly.
It's a two floor flat in a converted house (probably '80s conversion) and has only two circuits - one for all the sockets and one for all the lights - and so in the new CU I installed one rcbo for each circuit. Circuits all tested fine for insulation resistance, continuity and Zs, but the lighting rcbo was tripping occasionally within a couple of days. I retested (circuit and rcbo) and all seemed fine, and it's been OK for about a month, until it tripped again yesterday and would not reset.
I went back this evening expecting to change a faulty rcbo but decided to run the circuit tests again too. I removed L&N from rcbo and went to do insulation resistance between them and the earth bar, and my tester objected that it was a live circuit. After removing the cpc from the earth bar my meter tells me that I have 220v between all conductors of the lighting circuit and the earth bar. Loop impedance between lighting live and earth bar is 80ohm, and hence (I suppose) I was not getting a shock when testing.
I assume that this must be an induced voltage from somewhere, but it's not from the socket ring main as the voltage was still there even with that circuit turned off too. I guess too that this is the cause of the tripping, but even if it's not it needs to be sorted.
I'm due back there tomorrow to try to trace the problem, but any hints as to where to start looking for what would be appreciated. The lighting circuit is looped in to the switches so it's not too hard to take the circuit apart to test individual cable segments, but that could be quite random unless I've got some sort of plan.
It's a two floor flat in a converted house (probably '80s conversion) and has only two circuits - one for all the sockets and one for all the lights - and so in the new CU I installed one rcbo for each circuit. Circuits all tested fine for insulation resistance, continuity and Zs, but the lighting rcbo was tripping occasionally within a couple of days. I retested (circuit and rcbo) and all seemed fine, and it's been OK for about a month, until it tripped again yesterday and would not reset.
I went back this evening expecting to change a faulty rcbo but decided to run the circuit tests again too. I removed L&N from rcbo and went to do insulation resistance between them and the earth bar, and my tester objected that it was a live circuit. After removing the cpc from the earth bar my meter tells me that I have 220v between all conductors of the lighting circuit and the earth bar. Loop impedance between lighting live and earth bar is 80ohm, and hence (I suppose) I was not getting a shock when testing.
I assume that this must be an induced voltage from somewhere, but it's not from the socket ring main as the voltage was still there even with that circuit turned off too. I guess too that this is the cause of the tripping, but even if it's not it needs to be sorted.
I'm due back there tomorrow to try to trace the problem, but any hints as to where to start looking for what would be appreciated. The lighting circuit is looped in to the switches so it's not too hard to take the circuit apart to test individual cable segments, but that could be quite random unless I've got some sort of plan.
