Discuss Rcbo's tripping-some advice needed please in the Electrical Forum area at ElectriciansForums.net

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Hi all,

In Feb I was asked to fit a new bathroom light and extractor fan in a bathroom. There was already a supply for bathroom light so all I had to do was take a feed for fan isolator. I fitted the light and fan did the nessercary tests and filled in certificate everyone happy. The installation is a TNS with all circuits protected by individual single pole rcbos. At the beginning of May I got a call saying that the upstairs lights Rcbo( which included the bathroom lights/fan) and the cooker rcbo had tripped on two occasions together, once a week apart and then 4 days. I went back to property stripped back and disconnected what I had done and cooker circuit, did Ir test at 230 then 500v. I also did a ramp test with all accessories disconnected and again with everything reconnected to see if any earth leakage. I also did IR test for rest of circuits as a whole. I could not find anything obvious so asked customer to keep a log of times of tripping to see if any pattern emerged. I asked him to contact me when it trips agin and I would come back over.

I didn't hear anything for almost three weeks, so I emailed the customer and he said nothing had tripped. Then two days later I got an email saying that the upstairs lights had tripped again and the downstairs sockets rcbo had also tripped during the night.

I am going back tues armed with clamp meter and was wondering if anyone has any advice or suggestions. There always seem to be two rcbos tripping together at same time. The upstairs light and another rcbo, not even the same ones. If there was a neutral to earth fault wouldn't the individual rcbo trip first as the fault would go through rcbo first before the link to the neutral bar? There also only one outside light which I have checked for damaged or water ingress

Thanks
 
You could try insulation resistance test between the neutrals of the ciruits that are tripping , cables may have rubbed together durring the original install ,so couring a neutral in balance between the rcbos .
 
Neutral earth fault on the upstairs lighting, when there is enough current passing through the fault it's tripping the lighting circuit and also the circuit that is passing the current through the neutral earth fault. Is there any way you can split the upstairs lighting in half and add an extra RCBO in the board? This way you might be able to narrow it down a bit?
 
It just might be the two RCBO's tripping are co-incidental. The lighting, is there any outside/security lights, half full of water.

Good luck, some peoples like fault finding. Me, I'd rather have me toenails pulled out with pliers. Happy hunting OP.
 
The suggestion is that you added a fan and the tripping started. I guess the tripping may have been occurring prior to your work. I should ask them. Because why would adding a fan cause tripping?? I am a bit suspicious, that maybe you have been led to take on something that is historic.
 
The lighting RCBO could of tripped due to a lamp blowing. It may be nothing whatsoever to do with the RCD element of the device. Be very wary of clients info on what tripped and how often. In my experience with these occasional tripping issues you never get the full story.
 
Hmm i had a similar issue with garden lights i installed when i were a young lad, i done a really good job bar one light, i terminated the enclosure tight onto neutral and the client said all he done was touch a light and the circuit tripped.
I were arrogant back then i straight away thought yea dont blame my light i done all the IR testing so no nothing can be wrong.
end of the story turned out to in fact be the light he touched, my point is IR testing only highlights an issue on the circuit at that moment in time.
 
The lighting RCBO could of tripped due to a lamp blowing. It may be nothing whatsoever to do with the RCD element of the device. Be very wary of clients info on what tripped and how often. In my experience with these occasional tripping issues you never get the full story.
I agree with Wirepuller and with that i would check cheap looking LED lamps as you will be IR testing with these lamps not in use which wont pick up any leakage, is there anything plugged into the shaver socket maybe?
 
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