I'm out with the kids. A phone notification message pops up. It's an email from the CCTV system at home, some cameras have gone offline. Only, I notice, the cameras not on a ups backed supply. Hmm. Is there a power cut or has the RCD.. I'm cut off mid-thought by another notification. It's a WhatsApp from my partner at home. The RCD has tripped. Well, that explains the cameras. I talk my partner through resetting the RCD, it's one of those that has a mid-position 'trip', and has to be switched fully off before back on again. The power comes back, all is fine. I ask what was running at the time, thinking of likely culprits such as the washing machine or dishwasher, something that mixes water with electricity? But no, nothing was on. Ok, that's curious. A phantom trip maybe? But the power stays on and I think little more about it.
A couple of weeks goes by with no further trips.
Saturday, a couple of weeks later. The kids are watching TV. I'm in the study. The RCD trips. I jump an absolute mile, the consumer unit is just above the study desk and the trip goes off with a collosal bang. The kids can't immediately figure out what's gone wrong with the TV but they blame NetFlix! How sweet. Ok, obviously there's something wrong, somewhere. But, again, we're not using many domestic devices so what's the cause? This time the RCD trips out immediately upon reset so I switch the ring circuits off and try them one at a time. The fault seems to be on the ring that services the rear of the house. It's raining, so I wonder if water has got into the garden socket spur. Thanking the double pole isolator I turn the garden off and reset the RCD.
My house has a split consumer unit with the RCD protecting the ring mains and cooker. It means the lights stay on during the trip, which is good. But the fault could be on anything connected to any socket or ring main. My house is absolutely full of electronics and the faulty item could be anywhere. Still, it proves the RCD works I suppose. I have a feeling this fault is going to need to get worse before it gets better.
When the weather clears up I investigate the garden sockets. There's a little moisture in one of the socket housings, but nothing on the terminals. There's a Sonoff Mini WiFi switch in there for remote power switching, could moisture have gotten into that? It doesn't look hugely likely, but we've had no trips since I isolated the garden sockets, so maybe.
Friday evening, a week later. The kids are home, dinner's in the oven. BANG. The RCD trips again. So it wasn't the garden sockets. I can't figure this out, none of the usual culprit devices are on, and the oven wasn't on when the RCD tripped before. I reset the trip and unplug as many kitchen appliances as I can in case one has somehow developed a fault that causes a trip even while it's not in active use. Me, clutching at straws? Slightly, yes.
Later the same evening, my partner and I are watching TV, not much else going on. It's cold outside so the heating is running in the background. BANG. The trip goes again. Half of me is pleased, I've pretty quickly eliminated a bunch of kitchen appliances as the cause. The other half of me is now getting a bit worried. Is it even a device? What if a rodent has half-eaten through a cable under the floor? It's getting worse, whatever it is.
I've got an outside light fitting that, thanks to some unfinished DIY, runs off the ring main. Could that be it? It's a bit of an old fixture, the PIR timer gave up a while ago so something on the PCB inside has definitely failed. Maybe it's got worse and is now tripping out the house? I disconnect it. Later I dismantle the light fitting, destroying it in the process as I check over the PCB. All dry, no obvious sign of arcing either. It doesn't look like this was the culprit and now I need to replace the whole fitting. Sigh. So I'm back to unplugging more devices. Now it's got to the point of asking the household to ensure the kettle, toaster, microwave, power showers are all left unplugged or turned off at their isolators when not in use. It's a right pain in the butt but the only way I'm ever going to narrow things down.
Sunday morning. I wake up and meet a child on the landing. "My bedside light isn't working and Alexa won't listen to me". Uh oh. I hot-foot it to the consumer unit. Confirmed: the RCD tripped sometime overnight, that's a first, we definitely weren't using any devices then. The UPSes have done what they can; the networking and WiFi UPS is still up but the server UPS has run out of juice, the power has been off for over an hour by now. I spend the morning correcting the ESXi configuration to ensure all the VMs restart properly after a power outage. Mental note, in future, check the auto-start config of new VMs upon creation.
We've recently redecorated the kids' bedrooms and fitted them with new power cube/USB chargers, could these be the cause? They're the usual slightly dubious Chinese products from Amazon. No, my partner remembers the first trip occurred before we put those in. Their memory is clearly better than mine, all these trips are melding into one long unpleasant memory in mine now. I am really starting to run out of devices to unplug now. By this point I am actively expecting the RCD to go any second. Every little noise in the house makes me jump - was that the RCD tripping out? My nerves are pretty shredded and this stopped being fun ages ago.
Later the same day. Sunday afternoon. BANG. There goes the sodding RCD again. This time I notice the consumer unit has got a bit warm. That isn't right. There's a slight fizzing sound too, ok, immediate action stations, that is very much a Bad Situation that needs urgent investigation. I kill the power to the whole board and undo the cover, noting the sign that says to call an electrician, but at the same time wondering how long it would take to find one on Checkatrade at this hour. The main live busbar is hot to the touch and I soon spot the screws on the connection into the RCD are so loose they're barely holding the wire onto the bus bar. How long have they been like this, I wonder? Have I dodged a catastrophe?
I tighten the screws and give everything a thorough wiggle. Nothing else is loose. Good. Could the dodgy bus connection into the RCD have caused the trips? Or have the trips and subsequent regular resetting of the RCD resulted in enough wiggling of things to finally loosen the bus bar screws enough to cause arcing? I re-fit the cover and switch the house back on. Hopefully that's it for the trips. The consumer unit remains cool now but obviously needs checking over by a professional ASAP.
A few days later. I'm on a train in the evening, heading off to a gig. My partner's at home. The phone bleeps. Emails from the CCTV system. I know the pattern now. I message my partner, has the power tripped again? Yes. Plunging them into darkness in the garage, too, they report. What's worse, the RCD won't stay on. It trips out immediately upon reset. WHY do these things always get significantly worse when I'm away from home?
I've tried just about everything else but have one major system yet to prove: The heating system. It's the one system I really don't want the fault to be in, but in the back of my mind I'm aware I haven't yet checked it. I get my partner to isolate it. Thankfully, now the RCD stays on upon reset. As a test, my partner switches the heating isolator back on and BANG, the RCD trips immediately. The heating is left isolated for the night and I enjoy my gig. Progress at last! I have a culprit. But a fault with the heating system feels like an expensive one to fix. I contact my plumber and arrange a visit for a couple of days' hence; servicing the boiler is something I always leave to a professional. I envisage a failed control board, a leak inside onto electric terminals or perhaps a leaking pump.
A couple of days later. Fortunately the weather has been mild so we don't notice the lack of heating. The kids are quite pleased not to be able to have baths or showers. My partner less so. I decide it's worth me having a look at the parts of the heating system that don't involve gas, it'll be less for the plumber to investigate. The heating system in this house is a standard UK Y-Plan system comprising boiler, pump, 3-port motorised valve, a hot water tank with stat, a room stat, a header tank and the radiators. There are only a few places where electricity meets water so I have somewhere to start looking.
The hot water tank stat checks out, nothing loose, no fraying wires.
Next, the 3-port motorised valve. I lift the cover. Inside is a bit of a mess, at some point the valve has been replaced and chocolate blocks have been used to connect the new wires onto the old cable. I carefully lift the blocks checking for any loose connections. One block is resting on a chassis screw and as I lift the block to look closely it quickly becomes apparent that the plastic insulation has completely worn though. The brass terminal is resting and making contact with the earthed chassis.
Fault: found!
Knowing the cause, the intermittent nature of the trips is neatly explained by slight expansion of the metalwork when the heating runs: sometimes it expanded just too much and made contact with the terminal. The wearing-through of the chocolate block can be explained by vibrations in the pipe over many years slowly filing away at the plastic surrounding the terminal; the 3-port valve is located very close to the system pump which will be putting tiny vibrations into the metalwork.
The plumber visits and replaces the chocolate block, ensuring the new one isn't resting on the screw. They are very impressed with my discovery of such a tiny fault. The boiler is also serviced and given the all-clear.
The mystery of the (actually not) phantom trips has finally come to an end.
I now just have an outdoor light to replace, and a consumer unit to get serviced. And I think I'll replace those chocolate blocks with Wago connectors, too.
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