Confused - lighting circuit.

Liam Regan · Sunday at 3:08 PM

Hello, any help will be appreciated. One of the RCDs tripped that protected the downstairs lights, kitchen and upstairs sockets. Process of elimination showed the issue to be with the downstairs lights. At the time it tripped the two kitchen lights had been on for sometime. Separate switches for them. I switched the hall light on and about 5 minutes later the circuit tripped.

I assumed it would be the hall light that was the issue. One switch two lights. I disconnected both ceiling roses. Went to switch the circuit back on and it tripped again.

I have had problems with the hall lights about two months ago that I thought I resolved. Why suddenly go now?

One by one I disconnected every ceiling light. The circuit still trips.

Am I missing an elephant in the room or is it time to call an expert.
Most of the ceiling roses have connectors as per image. Not like the ones i see in guide videos.

Geoff1946 · Sunday at 3:31 PM

Unfortunately random time RCD trips can be hard to diagnose. The fault doesn't even have to be on the same circuit, because adjacent circuits on the same RCD can interact depending on overall circuit loading.
Hence looking at the last item to be switched is no indication at all if it was several minutes ago.
It could be a faulty appliance on the ring circuit.
You probably need help.

Liam Regan · Sunday at 6:46 PM

Geoff1946 said:
Unfortunately random time RCD trips can be hard to diagnose. The fault doesn't even have to be on the same circuit, because adjacent circuits on the same RCD can interact depending on overall circuit loading.
Hence looking at the last item to be switched is no indication at all if it was several minutes ago.
It could be a faulty appliance on the ring circuit.
You probably need help.

Thanks for your quick reply. Of note when i switched the lighting circuit back on, which immediately tripped, there was nothing else on in the house other than usual stand by stuff. Could it still be surrounding circuits.

Geoff1946 · Sunday at 7:49 PM

You did say it tripped a few minutes after switch on. If it goes immediately then it's more likely where the fault lies, but still not 100%.
I'll try to explain; When you switch on a load the current drawn slightly raises the potential on the neutral, due to the resistance of the cable. That small potential is applied to all the neutrals which share that RCD. Note that neutrals are not switched by normal MCBs.
Now if one of those dormant circuits has a short, or partial short, to earth, some current will flow and that may be enough to cause the RCD to trip.
An electrician has equipment which can measure for any such short circuit and will quite likely disconnect individual circuits at your consumer unit in order to test them.

SPECIAL LOCATION · Sunday at 10:42 PM

Liam Regan said:
Hello, any help will be appreciated. One of the RCDs tripped that protected the downstairs lights, kitchen and upstairs sockets. Process of elimination showed the issue to be with the downstairs lights.

Am I missing an elephant in the room or is it time to call an expert.
Most of the ceiling roses have connectors as per image. Not like the ones i see in guide videos.

Unless you have physically disconnected all of the neutrals inside the consumer unit from the every other circuit that shares the same RCD, during your testing of the lighting circuits then you have eliminated nothing.

By the sounds of it, the elephant in the room appears to be that you have not done any formal testing with suitable meters/testers etc. to check insulation resistance, RCD operation etc.??

If the "guide videos" you have been watching don't show you how to to proper dead circuit testing when investigating a fault, or mention what test equipment you need, then they are probably not the best quality instruction guides to follow..?
(I have seen far too many wanna-be video celebrities producing very dubious electrical guidance!)

You fault could just as easily be on a dodgy socket.. or a faulty appliance still plugged in...
As the current from the lights can travel to the common neutrals at the CU, and back out of the CU along a neutral, into a socket, then into the back of a faulty appliance that has a path to earth from its internal neutral wiring. This cant happen it you have disconnected the shared neutrals.

A faulty appliance/socket with a single pole switch does not need to be turned on to allow electricity from a different circuit that shares the same RCD, to cause the RCD to operate.

This is why current wiring regulations do not recommend shared RCD's in domestic dwelling. Although they are electrically safe, they can be quite inconvenient in the event of faults.

Liam Regan · Monday at 7:00 AM

SPECIAL LOCATION said:
Unless you have physically disconnected all of the neutrals inside the consumer unit from the every other circuit that shares the same RCD, during your testing of the lighting circuits then you have eliminated nothing.

By the sounds of it, the elephant in the room appears to be that you have not done any formal testing with suitable meters/testers etc. to check insulation resistance, RCD operation etc.??

If the "guide videos" you have been watching don't show you how to to proper dead circuit testing when investigating a fault, or mention what test equipment you need, then they are probably not the best quality instruction guides to follow..?
(I have seen far too many wanna-be video celebrities producing very dubious electrical guidance!)

You fault could just as easily be on a dodgy socket.. or a faulty appliance still plugged in...
As the current from the lights can travel to the common neutrals at the CU, and back out of the CU along a neutral, into a socket, then into the back of a faulty appliance that has a path to earth from its internal neutral wiring. This cant happen it you have disconnected the shared neutrals.

A faulty appliance/socket with a single pole switch does not need to be turned on to allow electricity from a different circuit that shares the same RCD, to cause the RCD to operate.

This is why current wiring regulations do not recommend shared RCD's in domestic dwelling. Although they are electrically safe, they can be quite inconvenient in the event of faults.

Hi, thanks for your reply. The guides I was watching related to lighting circuits, not fault finding, as pointed out I had wrongly assumed that was the cause not knowing how the negative is a shared line.

I will have a go at unplugging everything later today, if this fails I will call an Electrician.

Again thanks everyone for the prompt replies.

Murdoch · Monday at 8:02 AM

In the meantime you could make a note of what you are using when it trips BUT in the case of a shared RCD tracking down faults can be timely and complicated.

When you pay a spark to investigate ask them to confirm the tests and results in writing so if they don't locate a fault you can have these results to hand when its next investigated.

I'd be looking at the earth leakage for the property and paying close attention to the tripping characteristics of the RCD's because they can and do get more sensitive with age.

UNG · Monday at 10:32 AM

SPECIAL LOCATION said:
Unless you have physically disconnected all of the neutrals inside the consumer unit from the every other circuit that shares the same RCD, during your testing of the lighting circuits then you have eliminated nothing.

Had one a while ago on a dual RCD CU and the fault was not on the side of board where the RCD was tripping. The strange bit was the RCD that protected the faulty circuit did not trip and when tested operated as it should it was a bit strange that the fault bypassed that RCD and tripped the RCD on the other side of the CU, found the fault and repaired it
The only explanation I could come up with for the odd tripping was that one RCD was slightly more sensitive when tested

Liam Regan · Monday at 10:48 AM

UNG said:
Had one a while ago on a dual RCD CU and the fault was not on the side of board where the RCD was tripping. The strange bit was the RCD that protected the faulty circuit did not trip and when tested operated as it should it was a bit strange that the fault bypassed that RCD and tripped the RCD on the other side of the CU, found the fault and repaired it
The only explanation I could come up with for the odd tripping was that one RCD was slightly more sensitive when tested

I have just finished pulling all the sockets from that side of the RCD to no avail.

Who needs downstairs lights. It's almost summer

.

ProDave · Monday at 10:57 AM

Neutrals as well?

Liam Regan · Monday at 11:31 AM

ProDave said:
Neutrals as well?

Poor wording. Pulling plugs to check for dodgy appliances / devices. My investigation is over. Time for an expert.
My son chose to do a mechanic apprenticeship, I said at the time he should do an electricians apprenticeship. Based on that the cost of the sparky will come from his Christmas present fund for making the wrong choice. That is until my car breakdown.

7029 Dave · Monday at 12:02 PM

Liam Regan said:
Poor wording. Pulling plugs to check for dodgy appliances / devices. My investigation is over. Time for an expert.
My son chose to do a mechanic apprenticeship, I said at the time he should do an electricians apprenticeship. Based on that the cost of the sparky will come from his Christmas present fund for making the wrong choice. That is until my car breakdown.

Good choice to get an electrician in with all the test equipment good luck.

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