No time like the present… 
I have a colleague who has a particular axe to grind over AFDDs another type of safety device, I keep meaning to pass the cable to him so that he can disprove the benefits of expensive safety devices!
In my house, the thing that trips RCD’s (and blows fuses in my HiFi) is ‘flash’ power cuts i.e. a cut that lasts just a few seconds before coming back on.
Any chance you’re getting these late at night for maintenance work on your supply?
I’m sure the power companies think they’re being helpful by making them so short, but they are often so much worse than a longer cut that allows everything to shut down properly before being asked to power up again. Really bad for 5 Naim power supplies to all ask for start up current at once!
I use an uninterruptible power supply on sensitive and important items like routers, switches, computers, Naim Core and the like to avoid the worst effects.
Thanks for all the responses.
Funny several of you should mention the fridge / freezer. When we came back off holiday a few months ago the power had tripped (literally the morning we were due back after a 3-week break) and now remember the only way to get it back on again was by unplugging the fridge from an extension cable we were using.
Once the RCD had been reset I plugged the fridge directly into the wall and everything was fine again.
The fridge is only 5 years old so will be annoying if this is the cause. I have a long cable so will look to run the fridge of another part of the circuit to see if this causes issues.
We had a random RCD tripping recently and it was the fridge. Took a while to narrow down.
We used a plug in RCD unit that would trip first before the main RCD unit. We just shifted it around each device until the portable plug in RCD tripped while the main RCD didn’t. If consumer unit RCD tripped as well, we knew it wasn’t the bit of kit plugged in to the portable one!
You’ll need a plug tester that has a test that deliberately trips RCD units just to make sure the portable one is more sensitive that the consumer unit RCD. It’ll trip first leaving the main one untripped
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We had a similar problem, it turned out to be the element in the cooker oven, we knew it was related to the oven but couldn’t pin it down exactly what it was.
Two engineers and several elements later it was sorted,even one of the replacement brand new elements had an earth fault.
It was so frustrating but all good now.
So, I’ve plugged the fridge into the sockets that run off the main circuit board (separate to the lounge). The RCD (on the main consumer unit) tripped this morning but the MCB in the lounge didn’t trip.
I’m slowly unplugging all the equipment to see what’s causing it but might go down the route that @A-Fin has suggested.
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Maybe it’s just me, but… I’m having trouble visualising your distribution arrangements!
Any chance of a block diagram showing where rcd and mcb are located?
Oh - I like @A-Fin’s diagnostic too
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Here you go:
Yesterday:
The RCD highlighted in green tripped
The MCB in orange tripped
Today:
I plugged the freezer into the Kitchen sockets (that run of the Main Consumer Unit
The RCD highlighted in green tripped
Estimated age of units:
Main Consumer Unit = 30+ years old
Extension = 15+ years old
Garage = May 2022
Circuits only require one MCB to protect them, and are prone to tripping if more than one are connected in series. It looks like you have three breakers in series on your garage wall sockets, so it’s no great surprise that they are tripping.
Apologies for the confusion, those should ave indeed been wall socket images.
Diagram updated.
So your garage consumer unit runs off a circuit in your living room that also has wall sockets on it?!! I’m beginning to think you need your whole house rewiring.
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I’ve just checked and I was mistaken, there are no sockets between lounge fuse board and garage fuse board.
Apologies for the confusion
Adding to the MCBs in series issue, it looks like the MCB in your lounge that supplues the garage consumer unit is only 6Amp? That would be just about right for a lighting circuit, and not suitable for running wall sockets, let alone a whole extra consumer unit.
All that runs in the garage is as follows:
- CCTV
- Garage doors (that open twice a day)
- Socket for charging a phone / drill (used one a month)
Note: This garage unit had never tripped.
In that case it probably makes more sense to have a 6 amp MCB in your garage CU for the sockets. Although that isn’t going to solve your main issue here
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I have the same problem of occasional RCD tripping on my B circuit and I don’t know what is causing it, there is nothing that is not totally random about it. Thought I had fixed it as nothing for over 2 months but went again last night.
I had an electrician visit who tested and found nothing wrong. Other local electricians just laugh and say good luck fixing that!
I have a strong suspicion it might be the fridge freezer so will switch it to the A circuit and see what happens.
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Frustrating isn’t it, and it’s not as if you can switch the fridge/ freezer off for a few days to test either !!!
No, quite and I am away for a couple of weeks from Saturday which makes it a bit more concerning.
OK thanks for the advice.
One thing I have spotted is that my RCD is rated with a tripping sensitivity = 63a (image below) but the total load of all MCBs exceeds this value:
Right hand MCB’s: 32 + 16 + 6 = 54
Lounge MCB’s: 6 + 6 + 20 = 32 (86)
Garage MCB’s: 6 + 16 = 22 (108)
TOTAL = 108
Should I look to swap out the RCD for a tripping sensitivity of 100a or 80a ?
Note: The main switch is rated at 100a
