Electrics tripping RCD

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Timnofinger

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Recently moved into this old house which was completely rewired in about 2000. It has a Hager 12 way CU with type C MCBs. The RCD, rated at 30ma, is randomly tripping 2 or 3 times a day. None of the MCBs trip and we have driven ourselves mad disconnecting appliances and turning off circuits to identify the source of the problem. My understanding is there is likely an earth leakage on the neutral side which may be cumulative from more than one source. An electrician friend of a friend, no longer practicing, suggested replacing CU with RCBOs but thought this might not solve the problem but at least identify the circuit at fault. Alternative would be to get an electrician to test the individual circuits, but I don't know what would be involved and how long this would take. Money is tight so I would appreciate advice on how to proceed, specifically how to identify the level of electrician able to undertake a forensic investigation if that seems most suitable. Thanks for any advice.
 
RCBO board would likely still trip, just less inconvenient since only the affected circuit would trip. still won't fix the problem though

you need someone who knows fault finding. pretty much any electrician would be able to identify the affected circuit in less than 30 minutes, especially if its constantly tripping, although some faults do not show up easily. finding the actual fault may take 10 minutes, or all day. and then there is the fixing of it, which might be a quick fix, or it could be a return visit that's going to take hours
 
Could simply be a case of accumulated earth leakage

I would recommend you keep a note of each time it trips, and what you were doing and see if you spot a pattern
 
Thank you all. Andy you have confirmed my fears though I am encouraged that most electricians would have ability to identify a faulty circuit.
Murdoch we initially thought drawing hot water and firing up the Combi was a trigger. It was spurred off a lighting circuit but this is now on its own MCB. We've also disconnected the outside lights, live and neutral from MCB. RCD tripped this afternoon when no one was in the house.
Binky yes only one RCD. I have a multi meter, is there a safe test I can do on fridge and freezer? It's not really practical turn them off.
 

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Timnofinger said:
I have a multi meter, is there a safe test I can do on fridge and freezer? It's not really practical turn them off.
Click to expand...

A multi meter is more use with electronics than "electrics"
You can turn your fridge and freezer off for several hours with no problem, they are very well insulated to keep the cold in. Just remember you have un plugged them (so you can plug them back in 6 hours later, and do NOT open the door as it lets the heat in.)

The compressor on a fridge/ freezer does not run all the time, its "random" (It actually only comes on when the inside gets warm, so unplugged is not a problem and any food will "NOT go instantly off" ) Oh, take the milk out of the fridge first, you will want a cup of tea while you wait won't you.
 
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So the place was rewired, but nobody changed the board, which is very much out of date. So, at a rough guess, there's probably nothing wrong with the wiring, but build up of earth leakage from multiple appliances is taking out the RCD. My recommendation would be to get the board changed, ideally for RCBOs rather than two RCDs, and I suspect all your troubles will disappear.

I inherited a single RCD board when we moved house, 20 years ago. All was fine until Xmas morning when my wife had a fit as the electrics tripped out whilst she was trying to cook Xmas dinner. We have a twin oven range cooker, the small oven only ever gets used at Xmas, so damp in the elements was tripping RCD. Changed to an RCBO board, and now it never trips .
 
binky said:
So the place was rewired, but nobody changed the board, which is very much out of date. So, at a rough guess, there's probably nothing wrong with the wiring, but build up of earth leakage from multiple appliances is taking out the RCD. My recommendation would be to get the board changed, ideally for RCBOs rather than two RCDs, and I suspect all your troubles will disappear.
Click to expand...
The OP states it was rewired 20+ years ago back then we were stiil working to 16th edition so the board was probably changed having moved on 20 odd years through 2 regs editions and a handful of amendments to each of them it is getting to the point of the board needing an update to cope with a lot of the earth leaky equipment we have these days
binky said:
I inherited a single RCD board when we moved house, 20 years ago. All was fine until Xmas morning when my wife had a fit as the electrics tripped out whilst she was trying to cook Xmas dinner. We have a twin oven range cooker, the small oven only ever gets used at Xmas, so damp in the elements was tripping RCD. Changed to an RCBO board, and now it never trips .
Click to expand...
Thats dedication changing your own board on Christmas day so you could have Christmas dinner:)
 
Last edited:
Richard-the-Ninth said:
A multi meter is more use with electronics than "electrics"
You can turn your fridge and freezer off for several hours with no problem, they are very well insulated to keep the cold in. Just remember you have un plugged them (so you can plug them back in 6 hours later, and do NOT open the door as it lets the heat in.)

The compressor on a fridge/ freezer does not run all the time, its "random" (It actually only comes on when the inside gets warm, so unplugged is not a problem and any food will "NOT go instantly off" ) Oh, take the milk out of the fridge first, you will want a cup of tea while you wait won't you.
Click to expand...
The other "random" with many fridge freezers is the auto defrost or more precisely the failure of the auto defrost heater
 
kerching said:
Fault finding is an art
Click to expand...
I would agree you on fault finding being an art the problem is while you can teach the basic rules it can take years gaining experience to become proficient in finding the more difficult faults
kerching said:
and varies on every job. Two example…
I was called to a fault on a machine: 5 mins to find the fault and THOUSANDS of pounds to cure it

Another machine 2 days to locate a fault and the parts cost less than 10p
Click to expand...
Seen a few of them types of fault over the years
A couple I remember, one was a CNC lathe back when they were fairly new to industry and considered to be a specialist repair which took 2 - 3 days to get someone onsite when the customer deparately needed it working to complete an urgent order, so spent 50 minutes with my head in the wiring diagram, 10 minutes removing panels to get to where the fault appeared to be, 5 minutes of testing then off to order the £5 part to complete the repair the following day, the customer made the mistake of telling me how much the specialist engineer would have charged to repair it
One more recently was an earth fault I identified on the DNO network after the initial DNO engineer visit the cavalry were called up according to the customer they came in force about 2PM and left 10 - 12 hours later the earth fault was found to affect to half of the road and needed quite a bit of digging to fix
 
Thank you all. Having moved on from electricity is just like plumbing, it flows through pipes called wires I have learned more about earth leakage than ever knew existed. Depending on circumstance it seems to range through essential, inevitable, acceptable to being a harbinger of doom.
I have no documentation for the wiring, the house is 150 years old, and other than chatting with neighbours the only hard evidence I have is that it sold in 2001 for double what was paid in 1999. I believe the property was fully renovated and flipped during that time.
I am old and lived for decades in houses with wired fuses and only latterly using a plug in RCD with the electric lawn mower. I suspect bypassing the RCD would eliminate the perceived fault but of course I would never contemplate it.
On balance I think I shall get the board replaced with RCBOs hoping that this will prove a worthwhile upgrade for the future. Is there any particular type I should specify? Is this work certifiable since it is a replacement not an extension? Does it fall under Part P for suitably qualified electricians? Will I be left with a certificate showing the work has been done to code? Thank you all for your time.
 
Timnofinger said:
Thank you all. Having moved on from electricity is just like plumbing, it flows through pipes called wires I have learned more about earth leakage than ever knew existed. Depending on circumstance it seems to range through essential, inevitable, acceptable to being a harbinger of doom.
I have no documentation for the wiring, the house is 150 years old, and other than chatting with neighbours the only hard evidence I have is that it sold in 2001 for double what was paid in 1999. I believe the property was fully renovated and flipped during that time.
I am old and lived for decades in houses with wired fuses and only latterly using a plug in RCD with the electric lawn mower. I suspect bypassing the RCD would eliminate the perceived fault but of course I would never contemplate it.
On balance I think I shall get the board replaced with RCBOs hoping that this will prove a worthwhile upgrade for the future. Is there any particular type I should specify? Is this work certifiable since it is a replacement not an extension? Does it fall under Part P for suitably qualified electricians? Will I be left with a certificate showing the work has been done to code? Thank you all for your time.
Click to expand...

Whilst not an essential requirement.. the current wiring regulations (531.3.2) do recommend consideration of individual RCBO's for all circuits in domestic dwellings, to minimise inconvenience due to single fault disconnecting power to multiple circuits and/or unwanted tripping due to cumulative natural earth leakage from some electrical appliances etc..
 
Just so you can budget an Rcbo board change will be anywhere from £750 - 1300 depending on manufacturer and if your earth bonding requires updating at the same time.

Also if there are faults found on circuits these will need to be rectified or they won't be connected.

A good electrician will carry out some testing prior to even starting the board change to identify any issues.

If faults are found and rectified this will of course increase the costs.
 

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