One of the RCD’s suddenly tripped tonight as I was heading to bed. Literally turned off the TV and noticed the alarm fault light was on. Initially looked like one circuit but after unplugging everything, testing and re-testing the RCD is tripping randomly on other circuits too. Would this point to a faulty RCD? The only issue I can think of is there has been a bit of a buzz off the lighting MCB lately but that never tripped. Thanks in advance
RCD suddenly Tripping
- Thread starter bren1916
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The "alarm fault light" - where?
This is a reason why it would be a "good idea" to ditch any RCD "protecting" several circuits and replace it (and the MCBs) with RCBOs.
(Yes, there will be a cost, BUT you will then free up some space on your CU.)
However, if there is a future problem you will know the circuit actually affected.
Possibly.
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Agree. @bren1916 you may be able to find them for about a tenner each depending on your CU brand. They're a combined MCB and RCD.
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The alarm fault light was an indication that the power supply had been interrupted to the alarm system ie the Rcd had tripped..
Not necessarily. A fault on one circuit can sometimes cause a RCD on another to trip.
When an RCD trips it is almost never because the RCD is faulty.
Turning off the MCBs will not fully isolate the circuits. Pulling out all plugs and turning off all wall switches will be much better.
The cause is usually something watery where damp has leaked into an electrical part
In order of probability
Outside lights
Outside sockets and cables
Boiler or pump
Immersion heater
Kettle, tea urn, washing machine, dishwasher, Gaggia machine
Oven element eroded
Leaking bath dripping into room below
Nail into wall or floor puncturing cable
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Since 2008 the regulations have said "Every installation shall be divided into circuits, as necessary, to:
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation" among other requirements.
I have failed to see how the two RCD board has ever complied with that requirement, however it was cheaper, and many seem to get away with it, and we are instructed the client should be made aware of the problems of not having things like surge protection devices (SPD) but the decision is the clients on if to fit them. How I would inform the client not so sure, as I am not convinced, but same with bunched circuits on one RCD, it is down the the client to decide if they want to take the chance or not, we should measure the back ground leakage, which should be under 1/3 or the RCD rating i.e. 9 mA but that is when nothing is plugged in.
I have had a RCD trip, and tested the RCD and the RCD tester showed A1 (not the built in test button but proper tester) but on swapping the RCD the fault vanished, but back then there were no marking for type A and AC. In the main an RCD tripping means a fault.
The problem is the fault can be on either the line or neutral (both considered as live wires) so turning off an MCB does not isolate the circuit, so for the user, you need to look at likely causes. You don't have an insulation tester
RCD tester 
or clamp on ammeter 
so you can't really test yourself, all you can do is guess on likely causes.
So in the main down to water ingress, so any items outside like Christmas lights or any other outside lights, or any items which use mineral insulated heating elements the insulation is hygroscopic that is it attracts moisture, so if end seals get damaged it will absorb water. So this includes the cooker, immersion heater, frost free freezers, and washing machines.
Class II items are very unlikely to cause tripping (No earth connected) but any class I item may, just a bit of damp toast in the toaster is enough, as an item dries out, it may stop leaking, so using grill may dry out oven elements for example.
So anything that is not in use, unplug, and turn off cooker isolator when not using, try turning off immersion heater at the FCU (fused connection unit) as in the main the switches in them are double pole.
Items like your washing machine normally only switch the line, so the neutral of the heaters is still connected when switched off, so only way is unplug.
Normally I would say get an electrician, but I know it's Christmas so may not find one, so trying to list likely problems. It is so easy with meters, and so hard without.
I have all RCBO's but again Christmas so getting the RCD removed and replaced with RCBO's will not be easy, that's some thing to consider for the future.
My house the sockets are split front and back of house, so easy to run extension leads from living room to kitchen to run freezers off a different supply, with low risk, if the cooker is not on same RCD as rest of kitchen then that supply can also be used.
Swapping essential items from one RCD to the other can help identify which items are faulty, but extension leads up/down stairs is clearly to be avoided. Yesteryear homes were wired side to side with sockets, but when we went to duel RCD we wanted the lights to still work when the RCD for the sockets in that room tripped, so started to wire floor by floor rather than side to side, when I fitted two RCD to my last house in the early 90's you could not get the single module width RCBO's. That's my excuse anyway.
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation" among other requirements.
I have failed to see how the two RCD board has ever complied with that requirement, however it was cheaper, and many seem to get away with it, and we are instructed the client should be made aware of the problems of not having things like surge protection devices (SPD) but the decision is the clients on if to fit them. How I would inform the client not so sure, as I am not convinced, but same with bunched circuits on one RCD, it is down the the client to decide if they want to take the chance or not, we should measure the back ground leakage, which should be under 1/3 or the RCD rating i.e. 9 mA but that is when nothing is plugged in.
I have had a RCD trip, and tested the RCD and the RCD tester showed A1 (not the built in test button but proper tester) but on swapping the RCD the fault vanished, but back then there were no marking for type A and AC. In the main an RCD tripping means a fault.
The problem is the fault can be on either the line or neutral (both considered as live wires) so turning off an MCB does not isolate the circuit, so for the user, you need to look at likely causes. You don't have an insulation tester
RCD tester or clamp on ammeter so you can't really test yourself, all you can do is guess on likely causes.So in the main down to water ingress, so any items outside like Christmas lights or any other outside lights, or any items which use mineral insulated heating elements the insulation is hygroscopic that is it attracts moisture, so if end seals get damaged it will absorb water. So this includes the cooker, immersion heater, frost free freezers, and washing machines.
Class II items are very unlikely to cause tripping (No earth connected) but any class I item may, just a bit of damp toast in the toaster is enough, as an item dries out, it may stop leaking, so using grill may dry out oven elements for example.
So anything that is not in use, unplug, and turn off cooker isolator when not using, try turning off immersion heater at the FCU (fused connection unit) as in the main the switches in them are double pole.
Items like your washing machine normally only switch the line, so the neutral of the heaters is still connected when switched off, so only way is unplug.
Normally I would say get an electrician, but I know it's Christmas so may not find one, so trying to list likely problems. It is so easy with meters, and so hard without.
I have all RCBO's but again Christmas so getting the RCD removed and replaced with RCBO's will not be easy, that's some thing to consider for the future.
My house the sockets are split front and back of house, so easy to run extension leads from living room to kitchen to run freezers off a different supply, with low risk, if the cooker is not on same RCD as rest of kitchen then that supply can also be used.
Swapping essential items from one RCD to the other can help identify which items are faulty, but extension leads up/down stairs is clearly to be avoided. Yesteryear homes were wired side to side with sockets, but when we went to duel RCD we wanted the lights to still work when the RCD for the sockets in that room tripped, so started to wire floor by floor rather than side to side, when I fitted two RCD to my last house in the early 90's you could not get the single module width RCBO's. That's my excuse anyway.
Thanks for the replies, I have 2 CU’s and the faulty circuit is on the older one with only sockets, lights, alarm and shower running on that CU. I’m thinking it may be Xmas lights-related so have unplugged that and still tripping out. I have an electrician calling this evening and purchased an RCD 63a just to be sure as they’re closing at Noon for Xmas.
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Shower pull switches have a nasty habit of burning out due to loose connections
So with every MCB in the off position and sockets unplugged the RCD still trips on its own. I’m thinking it may be an issue connected to the other board in the extension although everything looks ok on that board with no visible issues ie everything is as it should be and powers to all those areas).
Thats a classic symptom of a neutral/earth fault. (The MCBs are single pole so openning the MCB doesnt remove the problem)
They can be absolute buggers to find. Its probably not a bad RCD - its doing its job!
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