Im pretty good at sorting my domestic electrics but this has got me stumped.

My Consumer Unit has 13 MCBs in 2 banks (bank 1 and bank 2) each with a RCD.

For the last two weeks I've been getting seemingly random trips of Bank 1 RCD.
No MCBs have tripped.

It suddenly got much worse three days ago with RCD 1 tripping 5 to 10 times a day - never at night.

Ive tried my hardest to discover which circuits are causing the RCD 1 trips. But it seems very random.

What is even more puzzling to me is that I can sometimes trigger a RCD 1 trip by switching on something that is on the Bank 2 circuit (eg a light switch or cooker or microwave. But it doesnt happen every time.
More often RCD 1 has tripped when nothing was switched on or off, as far as I can tell.

It was suggested that the freezers might be causing it as they are all on different circuits on Bank 1. So I moved all three freezers onto Bank 2 with extension leads. RCD2 has not tripped but RCD 1 still trips at odd times though not as frequently today as yesterday.

I wondered if it was a dodgy RCD unit as it tripped twice when I let the metal door of the CU close abruptly (RCD 2 didnt trip) so I changed it for a new one. No improvement.

We're away next week and I have arranged for an electrician to vist when we get back at the end of the month.

Anyone got a suggestion as to how switching something on Bank 2 can cause Bank RCD 1 to trip but not its own RCD 2?

Of note: The CU was installed and certified 2.5 years ago. No new electrics have been installed since then apart from Eon adding a smart meter about 6 months ago, in anticipation of them installing solar panels.

(After a 3 month wait Eon then said they couldnt install the panels as it was too difficult to place the scaffolding around my roof). Jules

I know it seems stupid but over the years the cables into each MCCB can become loose mainly due to to them settling due to temperature changes, I suggest you check all the wires from the MCCB's and check the live comb to the MCCB's my PC is slightly to the right of Genghis
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yeah - have done that when I changed the RCD.

Checked all sockets in the house with a 3 light tester.

Had all the sockets out and checked all connections for tightness.



Now I think about it , we've had a lot of rain since Wednesday and that is when the tripping started to get really bad - roads and field flooded. But now its drying up, and now the tripping is getting less frequent as today has passed.

Tomorrow Im going to check the connections from the main fuse and in and out of the smart meter, as these issues are after its installation but by several months. Its on the wall at the back of the house - never gets the sun on it.
Its interesting that the tripping never occurs at night, only during the day - could it be temperature or humidity related ?

My internet research indicates that smart meter installations can sometimes be well below standard; with loose or even reversed connections. Jules

I have had, in the past, circuits external to my house trip RCDs.

Mostly I have traced the problem by isolating various sub-feeds, it normally turns out to be water (rain) getting into either external lights or their junction boxes or switches.

Only once did it turn out to be rodent damage (normal mains cable buried in pipe to pond pump - seemed to be an ideal home for suspected Rat), Cables have since been replaced by armoured cables.

Have you outside electricity circuits, and can you isolate them?

As you know the RCD measures differences between the Live and Neutral currents, and therefore will trip if either finds a path to Earth.

Another possible cause (but not likely in domestic setting) is if 3-Phase is involved and heavy industrial machinery starting drags the Neutral-Point away from Earth.

PS thinking about it further
Could it be to do with your heating? A pump or similar would not be called overnight.
OR
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Have you got an old style light bulb low wattage somewhere that has not fully blown , and is touching then another time it’s not. Am no expert just a guess.

An RCD is looking for a current difference between the Live and the Neutral.
That current difference usually comes from a path to earth.
The fault isn't always in the Live conducter as technically the Neutral becomes Live whilst current is flowing through it. So a fault in the neutral can cause the RCD to trip.
That fault doesn't have to be a loose or 'nicked' wire as it could also just be a squashed wire, as that affects the integrity of the insulation.

The link between the two sides of the CU, whilst it should be separate, there could be a Neutral link.

You haven't said what is fed off the side that keeps tripping.
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EDIT
Just realised, I've virtually repeated IM's post

I’ve recently had the split circuit RCD protected board replaced with a full RCBO unit , combined MCB/ RCD breakers . It seems a much more practical solution . You only lose the one faulty circuit rather than multiple , and at that point it’s already an indication of that circuit needing attention one way or another . . If you have to call out a sparky to sort out your current problem it won’t be that much of an addition to get the board swapped out for RCBOs 2009 GS Auto Zermatt Silver - Sold June 21 after 10 years of ownership

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Jules I'd start by turning everything off and adding a circuit one at a time if that's possible. It could simply be a loose earth causing the trip or a faulty appliance tripping. My last trip was the time switch on the cooker which tripped everything and a faulty cheap Chinese oven bulb that kept tripping my mother's house.

Sometimes it's the simplest of things that cause the biggest heartache.

Stephen.

Ive now got all the freezers protected on a circuit from Bank 2 - which has never tripped - So I can live with that until the electrician comes.


Ian - Yes I do have external outdoor circuits - to the 2 greenhouses, sewage treatment plant (which runs continuosly), pond pump and a couple of sockets but they are all the Bank2 which doesnt trip.
And we've not had the central heating running yet, except for 1 hr at 0630) - All the CH electrics are on Bank 2.

Today RCD 1 started tripping occassionally from 10am and then every few mins from around lunchtime, but this evening hasnt tripped at all.

Yesterday switching on the induction hob triggered the trip even though the hob is on the other Bank (2). Today switching the hob didnt triggger it even though it was triggering "by itself".

Im out of ideas - I'll wait to see what the sparks says, but I can see swapping the board for one with RCBOs would help narrow down the cause.
Its difficult to switch off circuits and wait to see if it triggers when 1) triggering is so variable 2) the family want to use things. I 'll have a better chance of isolating things during the week. Jules

Last edited by jules on 20th Oct 2024 11:41 pm. Edited 1 time in total

DEG5Y wrote:

You haven't said what is fed off the side that keeps tripping.

Lighting circuits are not usually the problem, but if you can do without them through the day while you proove things turn them off. (With so many 'Chinese' imported metal light fittings and modern LED bulbs, it could be this cicuit!)
If it still trips, put it back on and move on.
If you can do without the Laundry circuit for a day, turn that off.
Again if it trips move on.
Apart from the pond pump you could turn off the garage circuit as long as your not in and out of the freezers they should be OK. Can you run a temporary feed to the pump from the otherside of the board?
Fianlly the kitchen.

Have you not been able to identify what appliances are running when it trips?

Don't just turn off, actually unplug anything you can do without.
Unplug because most things are single pole isolation which means there is still a path through the neutral. Should you have an imbalance on the neutral you can still cause a RCD to trip on a dead circuit, if your earth and neutral touch.

Does it trip more when it's raining?

Like I said before anything associated with water is on the suspect list but also anything that has a heating element.

ps.
I'm intrigued by the number of freezers. It's either to make a 'White Walker' feel at home, or the population of your local area is getting smaller and you buy a new freezer everytime someone goes missing!!!

Thanks Degsy

Don't just turn off, actually unplug anything you can do without.
Unplug because most things are single pole isolation which means there is still a path through the neutral. Should you have an imbalance on the neutral you can still cause a RCD to trip on a dead circuit, if your earth and neutral touch.

Yeah it took me a few hours of thinking to realise I needed to physically remove appliances as they have only a single pole switch.


Does it trip more when it's raining?
Definitely YES but its variable

Like I said before anything associated with water is on the suspect list but also anything that has a heating element.
Today Im going around disconnecting everything not essential

ps.
I'm intrigued by the number of freezers. It's either to make a 'White Walker' feel at home, or the population of your local area is getting smaller and you buy a new freezer everytime someone goes missing!!!
Haha We just grow a lot of vegetables and fruit - rarely need to buy them from shops and tend to buy meat in bulk from a local butcher. Jules

"Does it trip more when it's raining?"

"Definitely YES but its variable"


Could be pointing towards an external circuit.
If a circuit gets wet during the rain, it could take a while to dry out and therefore continue tripping.


Carport (lights & sockets) - How good is the IP rating (is the instalation good enough to maintain a high IP rating?), is the atmosphere damp?

Flood lights - Are they permanently on? Do they rely on a light sensor?

Just a few things to think about.

MartynB wrote:

I’ve recently had the split circuit RCD protected board replaced with a full RCBO unit , combined MCB/ RCD breakers . It seems a much more practical solution . You only lose the one faulty circuit rather than multiple , and at that point it’s already an indication of that circuit needing attention one way or another . . If you have to call out a sparky to sort out your current problem it won’t be that much of an addition to get the board swapped out for RCBOs

After checking everything in the garage and found no faults I started checking the external sockets and switches today.

In the 2nd box that I opened (feeding power to the sewage treatment plant) I found a broken neutral connector. The wire just fell out of the split brass connector when I took the face plate off.
The STP was still working though.

Click image to enlarge