RCD Spurious Trips

[pastitsparky]

Hi Guys, now here's a strange fault.
I have recently installed a new split MK consumer unit.
All circuits have high IR and the RCDs were tested by a Robin tester from all sockets and oven and lighting circuits etc, all good.
When I switch "off" my garage lighting, which is 3 fluro fittings the RCD trips on occasions, I suppose I could disconnect each fitting one at a time to see if the problem stops.
Any ideas would be appreciated.:wink5:

 

[MarkieSparkie]

Hi, welcome to the forum.

As you say the problem (only?) occurs when switching OFF the garage lighting circuit I am assuming you have checked the otherwise obvious possibility of rainwater or condensation build-up in the garage light fittings/accessories and found this not to be the case.

In that case, it is possible that you have a high standing leakage on the installation due to one or more failing appliance(s). The high standing leakage is not sufficient to trip the RCD by itself, but the addition of the switching transients from the garage lighting circuit is enough to occasionally push the RCD over the tripping point.
Test the leakage current (with a suitable leakage clamp meter) of each of the final circuits (connected to the tripping RCD) one at a time, ideally with all other final circuits isolated. You will probably find that you have one final circuit that has high leakage. Next test each appliance on that final circuit to identify the leaky culprit(s). Fridges, freezers, cookers, immersion heaters, irons and kettles are all frequent suspects.
If you fail to find any abnormally leaky appliances and you are satisfied that the high standing leakage is due to the normal accumulated leakage of the installation. Then you have two options, the best would be to split the final circuits over additional RCDs/RCBOs, however, the cheap short-term fix would be to add a snubber to the garage lighting circuit to tame the switching transients.

 

[markc123]

You've hit the nail on the head if it trips when its that circuit, problem with one (or more) of the fittings...garage's have a terrible tendancy to leak, could be water in a fitting...drying out, then leaking again thus causing sporadic tripping. You could have a trapped wire behind one of the flourescents if you've had it off recently, could be a number of things really. After typing that, i've realised you've said when you switch it 'off' ...it could even be a loose connection, and when making/breaking the switch its arching onto the earth terminal.

IR test the garage circuit again.