Raptor0014
Esteemed
- Reaction score
- 1,261
Evening all.
Been at a property the last couple of days that had suffered damage due to a surge. I got the power back on all circuits apart from the upstairs lights as it immediately trips.
Long story short I broke the circuit down and re-added room by room to narrow down the problem area, as no matter what test I did there were no apparent faults. Yet turn the lights on and the circuit trips. I ramp tested the RCD and that tripped at 24mA. The earth leakage with all the circuits on and under load with the particular RCD was 6mA.
The light in question is a weird GX38 CFL that sits in an alcove. But I removed it and wired a brand new pendant in and tried that. Immediately the circuit trips. The light works when wired in place of another light on the circuit. So the light itself isn’t faulty.
I removed all working loads in the circuit again
and had just this one light wired, circuit still trips.
I removed all other circuits from the RCD and had just this one light wired to the switch to rule out cumulative earth leakage and again circuit trips.
I tried the light and the pendant wired directly to the switch and both work fine.
So the problem seems to be a peice of cable approx 5m long that is buried in 2 walls and runs under the floorboards across the landing.
I wondered if the problem was maybe rodent damage on just one conductor that was giving a fault to earth via the rad pipes. But testing between the rad and the conductors gives open circuit. So it’s not that either.
I spent 20mins on the phone to technical support and they were at a loss as to the fault.
I did a R1+R2 and RN+R2 to check continuity. All fine.
I IR tested at 500v L-N, N-E and L-E and all gave >999MΩ
So there is a problem with the cable it seems. But testing it is not showing what it is.
At the moment I’ve left the suspect piece of cable between the load side of the switch and this one light disconnected. I’m going back in a couple of weeks to change the CU as the owner now wants a full RCBO surge protected unit. When there the only thing I can think left to do is run a new 5m long piece of cable directly from the switch to the light and see if the circuit still trips.
If it doesn’t trip then problem solved. But it still doesn’t make sense that any test I do shows no apparent problem. If it still trips then I haven’t a clue what the fault is.
So over to you knowledgeable folk. I’d appreciate any advice as it’s a real head scratcher and I can’t think of anything else.
Been at a property the last couple of days that had suffered damage due to a surge. I got the power back on all circuits apart from the upstairs lights as it immediately trips.
Long story short I broke the circuit down and re-added room by room to narrow down the problem area, as no matter what test I did there were no apparent faults. Yet turn the lights on and the circuit trips. I ramp tested the RCD and that tripped at 24mA. The earth leakage with all the circuits on and under load with the particular RCD was 6mA.
The light in question is a weird GX38 CFL that sits in an alcove. But I removed it and wired a brand new pendant in and tried that. Immediately the circuit trips. The light works when wired in place of another light on the circuit. So the light itself isn’t faulty.
I removed all working loads in the circuit again
and had just this one light wired, circuit still trips.
I removed all other circuits from the RCD and had just this one light wired to the switch to rule out cumulative earth leakage and again circuit trips.
I tried the light and the pendant wired directly to the switch and both work fine.
So the problem seems to be a peice of cable approx 5m long that is buried in 2 walls and runs under the floorboards across the landing.
I wondered if the problem was maybe rodent damage on just one conductor that was giving a fault to earth via the rad pipes. But testing between the rad and the conductors gives open circuit. So it’s not that either.
I spent 20mins on the phone to technical support and they were at a loss as to the fault.
I did a R1+R2 and RN+R2 to check continuity. All fine.
I IR tested at 500v L-N, N-E and L-E and all gave >999MΩ
So there is a problem with the cable it seems. But testing it is not showing what it is.
At the moment I’ve left the suspect piece of cable between the load side of the switch and this one light disconnected. I’m going back in a couple of weeks to change the CU as the owner now wants a full RCBO surge protected unit. When there the only thing I can think left to do is run a new 5m long piece of cable directly from the switch to the light and see if the circuit still trips.
If it doesn’t trip then problem solved. But it still doesn’t make sense that any test I do shows no apparent problem. If it still trips then I haven’t a clue what the fault is.
So over to you knowledgeable folk. I’d appreciate any advice as it’s a real head scratcher and I can’t think of anything else.