RCBO tripping - identify likely location - help.......

[GoodDIYjob]

Hi All,

Is there a effective, efficient way to go looking for a wiring fault tripping on downstairs lighting cct?

Ideally, for me to go looking with a multi meter but otherwise, if I have to, an electrician with a proper testing machine.....

Currently the cct is operating on an MCB. It is the only Cct that has a tripping fault... Guess that rules out a borrowed neutral upstairs / downstairs?

The house is predominantly a bungalow, but has two large dormers upstairs build over the back half of the roof slope. Some of the lighting cct is accessible on the other half of the ceiling / roof but not all!!!

So far, I've pulled all the pendants to check for connections and some wall lights and the kitchen down lights and fan. Nothing obvious found. There is another bank of 6 down lights I could try to pull out to trace connections and check.... How problematic are such problems to find......

Thank you

 

[EFLImpudence]

Is it an MCB or RCBO that is tripping?

Can you turn on the device?

 

[GoodDIYjob]

edit: an RCBO trips straight away, and was tried with an alternative, so it was "temporarily" replaced with an MCB to give service.

Slightly longer back story that I can fill in if you want with lots more detail but I don't think will add much to the following explanation

A registered electrician, who did the consumer unit change out, and BR competent person notification, could not identify the fault, I'm not sure he even did much looking and removed the RCBO that was tripping on the downstairs lighting and used a MCB to give service following change to a contactum CU with RCBOs and surge protection device or whatever it is called... .. He now can't be located or will not respond to me to resolve!!

I know he shouldn't of left it like that but that is how it is!!...

edit. previously the CU was a split board with no RCD protection on lighting...

 

[Murdochcat]

Borrowed neutrals are wired from the start so unless some cowboy spark has changed the fuseboard without doing all the necessary tests it’s not likely to be that.

Has this just started?

 

[Murdochcat]

be interesting to see the IR test results for the circuit

First things first - if you can take out all the bulbs on the affected circuit. Then turn the MCB on. If it holds then add the bulbs one by one slowly

Upstairs or downstairs

 

[GoodDIYjob]

Borrowed neutrals are wired from the start so unless some cowboy spark has changed the fuseboard without doing all the necessary tests it’s not likely to be that.

Has this just started?

Started a few months ago at time of CU change out to new RCBO unit, so fault probably inherent for who knows how long....anyone's guess..

be interesting to see the IR test results for the circuit
First things first - if you can take out all the bulbs on the affected circuit. Then turn the MCB on. If it holds then add the bulbs one by one slowly
Upstairs or downstairs

Downstairs.

I'll try, the Electrician has notified the BR part P but has not provided me either the EIC which would have test results. I can keep chasing but short of tracking down his home address for a visit, I don't have a full electrician's tester...
The MCB in place is holding. The RCBO the electrician originally installed was not and mumbled about a neutral / earth fault...

 

[EFLImpudence]

If I understand correctly and the circuit trips instantly (can't turn on) with an RCD but works alright with an MCB, then that would indicate a Neutral to Earth fault - somewhere.

 

[ericmark]

I had it with sockets supply, unplugged socket by socket until the fault cleared, and last item was the dishwasher, tested with insulation tester before getting a new one, not fault showed, plugged it back in, all working again no problem, put clamp around the CU tails, and all 14 RCBOs together only show an 8 mA leakage, not a clue what was causing the trip. And I have the test gear.

Look for where water can get in, any outside lights, switch them all off, if still trips, remove the bulbs. Next is any dimming switches, or other electronic switching.

What sound does it make, if any when it trips? The problem is we have no idea if earth leakage or overload, if overload then likely hear some sparking when resetting.

 

[GoodDIYjob]

If I understand correctly and the circuit trips instantly (can't turn on) with an RCD but works alright with an MCB, then that would indicate a Neutral to Earth fault - somewhere.

yes, exactly what the original electrician mumbled..

 

[GoodDIYjob]

I had it with sockets supply, unplugged socket by socket until the fault cleared, and last item was the dishwasher, tested with insulation tester before getting a new one, not fault showed, plugged it back in, all working again no problem, put clamp around the CU tails, and all 14 RCBOs together only show an 8 mA leakage, not a clue what was causing the trip. And I have the test gear.

Look for where water can get in, any outside lights, switch them all off, if still trips, remove the bulbs. Next is any dimming switches, or other electronic switching.

What sound does it make, if any when it trips? The problem is we have no idea if earth leakage or overload, if overload then likely hear some sparking when resetting.

thanks, yes - I checked outside lights thoroughly including junctions in roof space. There's no sockets in this case as it is lighting only. I could disconnect dimmers, there is only 1 or two downstairs.

It is not overload as the electrician mumbled neutral / earth leak. I didn't hear it but from what he said it was instant RCBO trip due to the leakage..

 

[GoodDIYjob]

Borrowed neutrals are wired from the start so unless some cowboy spark has changed the fuseboard without doing all the necessary tests it’s not likely to be that.

Has this just started?

Oh, ok. I though sometimes, especially upstairs / down stairs lighting, a neutral is borrowed from within the house, from say the downstairs lighting or vice versa because it was closer / more accesible at time and does not cause an over current situation but will cause an RCBO to trip because of the imbalance... Anyway, if that was my problem I would expect the other cct to trip as well and all other ccts have RCBOs on and are fine.

 

[AndyPRK]

So you could turn all the power off.
Turn off the problem light circuit MCB.
Disconnect the light circuit neutral from the bar.

Set your multimeter to ohms / 200R where is buzzes when the probes are connected.
Measure between earth bar and the light circuit N wire. If you get a reading it's possible you maybe able to find the fault yourself with that equipment. If the meter can't detect the fault, your going to need a spark with multi function tester or insulation tester.

If you do locate the fault, you could split the circuit in half (approximately) or at a convenient point by disconnecting all the wires LNE. (taking photo first).
Retest. If the fault is still present you know its the first part of the circuit. if fault gone, the latter, disconnected part of the circuit.
At this point you could reconnect the neutral at the CU, repower the circuit. Turn all the light switches on, and work out which lights have been disconnected and note down. Have a cuppa tea. Turn power off. Post. Consider what to do next

 

[AndyPRK]

Oh, ok. I though sometimes, especially upstairs / down stairs lighting, a neutral is borrowed from within the house, from say the downstairs lighting or vice versa because it was closer / more accesible.

It's a bungalow with later loft conversion

 

[EFLImpudence]

Wrong thread.

 

[ericmark]

A bulb

no earth, so can't cause an earth fault. Switch is the same in most cases. The cable, unlikely to be a problem, unless you have rodents.