I find these devices so fascinating. The complexity is mind-boggling. And considering the intensive labor to assemble, the price is a bargain.

(shovels breaker bits into baggie and mails back to owner with note "Works perfectly fine.")

This circuit breaker ain't going back together again. Now called a "Circuit Broken"

"Definite signs of sadness". Class. I might have to steal that phrase!

Ah, excellent - yes, saw Chris's (CJR Electrical) video about this. One thing I love about KZfaq is the community atmosphere between so many diverse technical channels.

My shop breaker gets tested regularly! How it’s tested, I will not say, only that it’s doing it’s job. 😂

Tripped accidentally; yeah, that's my story and I'm sticking to it!

I've always been fascinated by RCDs, ever since I became a property manager and learnt what they were and roughly how they worked. I've been in a few situations where RCDs have saved the lives of people I know. Fortunately I've had no known deaths of tenants from faulty RCDs, so I'm glad about that. Thanks for the video, I found it quite interesting! Looking forward to seeing the burnt-out one.

A most excellent exploration! Thanks Clive!

Clive, I've enjoyed Chris's channel for awhile now. This is one of two videos I've seen where he said he was going to offer/send equipment to you to play with & diagnose.

Super-Sensitive Magnetic Trip would be a pretty good bandname

"Showing definate signs of sadness" Excellent!

That's another good channel I watch...glad he caught that /before/ something had a meltdown.

I saw a video from - I believe Applied Science - where an unsmoothened half-wave DC of the AC outlet voltage was needed (so AC rectified by a single diode). He mentioned that he was very careful not to toch the DC, because it might not trip the RCD. So if I understand it correctly, that is the case if you have an AC only RCD. Never thought about that. I don't test my RCD monthly. I have some Linux small board computers, like a firewall, who run in read/write mode. They don't like being powered off unexpectedly. If they are just writing some data to the SSD, files may get corrupted. So I have to shutdown them properly before I can test the RCD.

Screwfix is the most disappointing escort agency I've ever used.

Thanks Clive. Interesting to see inside an RCD. Did not know that RCD are not over current breakers. Explains a lot. Had a similar experience in a hospital theatre in Australia with an older RCD. It would trip on power up of a diathermy during its internal checking . The diathermy does a short internal high voltage/high freq (300volts 480khz) test. Turns out that the RCD was sensitive to HF leakage . The newer RCD replacement had no issues. Hospitals normally have 10mA trip current RCDs

Thanks Chris Cjr and thanks you Clive for the Tare down was very interesting

love your work Clive :)

Big Clive I love your accuracy!

Very interesting thanks Clive.

You had me worried there for a minute, but luckily all my RCDs are type A. Apparently type AC has not been allowed for new installations since 1996 here in the Netherlands.

I do checking of that stuff regularly (german based) with specialized appliance tester/installation tester equipment. Judging from the setup and photo of the fuse box, I do not think that that RCD has been overloaded. Yes, the rated current in sum of all that RCCB is greater that 63A, but looking at the load behind that, it simply is unrealistic that they will draw that current over a longer period of time. Explanation: Usually cooking appliances will heat up for some minutes, but when the final temperature is reached, they will reduce the current draw resp. will give some short burst of energy every few seconds to maintain temperature. Same goes for ovens and that kind of stuff. As an example, where I did some measurements some time ago: You need about 0,5 kWh of Energy to boil some potatoes (one person meal...) in a pot in salted water. This takes about 20-25 minutes. Average value over time with 230 Volts=approx. 6 Amps. Even if you have 3 or maybe 4 platters going, you would not use 32A in average... Lighting is the same, so we don't talk about full throttle going on. Also the kitchen sockets usually are not used to full usage, so I would assume that sometimes that RCD has had a hard time going, but severe overload is different. A tripping RCD usually goes with leakage current going on, which can also occcur when lots of heating devices at the same time will do their thing- because some moisture between the coils generate some current path from L to PE and voila- you have your 15 mAmps that are sufficient to sometimes trip the breaker. At work we also use Hager RCD in our offices, and i found them to be quite fast- 20 ms tripping time and also near the low end of mAmps to trip them. A 30mA delta rated RCD is by standards allowed to trip at 15 mA, and has to trip at 30 mA.

My house has an entire subpanel for the kitchen, my house was built in 1939 so we’ve needed to add various subpanels over the years we have a main panel that controls a lot of the replaced lines in the house, and we have a hall subpanel that controls all of the old wiring (knob and tube) and we have the subpanel in the basement that controls the kitchen.

I saw Chris' video about this and was hoping for you to make the "follow-up" - interesting to see that the RCD was apparently fine!

Never knew Screwfix and B&Q owned by the same company, had to pause the video and go and look. Mind blown!!

I have tested my breaker near monthly, after watching the Technology Connections video on these.

Thanks, nice breakdown..

Don't know UK code, but in US, having multiple circuits that add up to more than the main isn't all that unusual. Sort of a 'duty cycle' thing. It'd be like saying, "Well what are the chances that both showers are in use at the same time someone is making tea in the kitchen and all the lights are on.... etc..." So although it could happen, the RCD current wouldn't exceed rated for very long and might only mildly heat up. And judging from the condition of those contacts, they didn't open under heavy load very often or ever. Love your video's BTW, watching you dissect things is a great way for me to get my 'tear stuff apart fix' vicariously. :)

I remember watching Chris’ video on thisn👌🏼 love the calculator BTW

Here in The Netherlands it's very common to have a large number of 16A breakers behind a 40A rated RCD. The main fuse is either 40A single phase or 25A three-phase so there is no need to have an RCD with a rating above 40A. Basically all breakers are always 16A, even for the lighting circuits. Chances that the water boiler, oven, washing machine, tumble dryer and dish washer are all heating at the same time is next to zero, but they can draw 16A each individually. If this situation would occur, the main breaker will trip and the RCD will still not see a significant overcurrent.

4:00 where Clive asks why they don't just have one model of breaker at the higher rated current? It would be interesting to get hold of a couple and take them apart - maybe the only difference between them is the label on the front panel...

Clive, I watched his vid the other day. Looks like he followed up and sent it to you. One of these days hopefully someone will send some breakers from the US for you to look at, especially a tandem breaker. It's not in the cards financially for me right now or I would go to the local big box home improvement shop and pick up a few of various types (brands are NOT interchangeable and different types between brands are NOT interchangeable as DIN rail systems are not used for residential panel boards here).

Place where I worked, we had a lot of old-style electro-mechanical chart recorders fed from a circuit protected by GFCI (what we yanks call RCD's). When we replaced the recorders with solid-state electronic ones, the GFCI's started tripping a lot. We found that the newer recorders (since they have a lot of electronics and such) were equipped with heavy line-filters to ground to project them and these filter caps were drawing a fair amount to ground. Since the whole distribution panels were fed from conditioned power, we just clipped the line filter caps inside the recorders to solve it (not the best way I'm sure, but it solved our tripping problem).

That's actually very nicely built unit.

nice calculator Clive :D

I often use electric Installation Tester to measure different things. The measurement "loop impedance" can cause RCD-tripping. When i simply start the measurement between a Phase and the PE in a circuit with a RCD without changing the settings of the tester it would trip the RCD instantly. There is a function in the Tester to generate this DC current to saturate the Residual current transformer of a RCD to prevent tripping. Depending of the used Type of RCD you can set different options to block RCD's from tripping.

Very nice to see the difference between UK and what I have seen in Canadian panels. UK components standards much much more paranoid = good. Thou in one of your other videos the plastic panel enclosure burned and so far all I have seem in Canada are metal enclosures, damm hard to burn. Guess it is cost vs occurance

You pulled out the sense coil and I thought "That is a beauty of engineering"

Tiny little magnet with a weak field in there, adjusted to get the correct field strength in the coil. In the top black protrusion, and turned to the correct trip current in the factory. This holds the armature just into position, so that the current through the coil is enough to reduce the field so the spring can release it. that is why it is in a small magnetic shield, as it is sensitive to magnetic fields around it, and without that shield it would be orientation sensitive due to the earth's magnetic field, and the current flowing in the busbars and wires near it. Circuit board is a pair of zener diodes to act as a voltage clamp, and some small capacitors to filter high frequency noise off the circuit. Likely yes the reason it was randomly tripping was DC in the system from half wave rectifiers and capacitive supplies, as they all have a small DC current flow from asymmetric rectification. This biases the permalloy sense coil into a non linear range and thus makes it act like a saturable reactor, so on one half cycle it will generate a current in the sense winding as it saturates, and randomly this current will be high enough along with harmonics to trip the coil.

I had nuisance tripping for years, mostly at nearby strikes during thunderstorms but it got worse: it could even trip when turning off the garden lights. Anyway.. kitchen got replaced. All was stripped off the wall. The fume hood socket appeared to have a tiny carbon track from live to earth on its inside ceramic body. Obviously that got replaced. No more nuisance tripping. If there's the tiniest slightest track laid down by that first lightning strike's overvoltage spike, the path is there. And it will build up at every consecutive time it flashes over. Good that I found it. I was already planning to dive into the garden wiring after the kitchen project was finished...

Given ~8kW per shower, and around 5-6kW per stovetop/oven Id say it was potentially grossly overloaded depending on who was showering and cooking.

"That can make them a bit sensitive to impact" . . . well there's the explanation, the kids in the house have learnt that a bang on the consumer unit trips the power off.

I was at an update meeting with a Hager rep last year (I think) and we were told that they are changing all of their 'standard' RCD's provided in split load boards to 100A rating, as generally that is the highest your cutout fuse will be and that is the only thing protecting the RCD should a fault occur with the RCD, that and to avoid this example of overload. I personally now fit RCBO boards where possible, much simpler when it comes to fault finding :)

I've always been careful about how many things are running on one circuit. In America our circuit breakers are mostly 15 and 20 amp. I've never overloaded a breaker, but the wiring in this house worries me a bit You're right about LEDs too, there's so many modern appliances that cause weird problems and interface. I got some things that you plug into that prevents these problems but I can't remember what they're called and would have to move some stuff to look.

Screwfix is actually owned by Kingfisher which is the parent company of B&Q, Castorama (France) and Brico Depot (Poland)

..."showing definite signs of sadness."😂😂😂 Awwww, it just needs a hug 🤗

If I remember rightly, "core balance detectors", (RCD's) that were first introduced in Germany back in the early 1970's were of the passive type with a permanent magnet, the field of which had to be calibrated exactly to meet the 30mA trip point. The problems with the early permanent magnet type was the inevitable decay in the remnant magnetic field resulting in tripping at lower and lower imbalance currents but the outstanding hallmark being no electronics (SCR's, Triacs) and hence reliability and better immunity to tripping on transients. I don't like the modern electronic types at all and false tripping is a major issue especially with the cheap types that use high gate sensitivity SCR's as the switching element. I know of numerous people here in Australia that have lost refrigerators and freezers full of food whilst they were away on holidays due to RCD's tripping, usually the refrigerator or freezer has to be thrown out as you can never get rid of the smell. Due to the creeping "doctrinaire self righteousness" of modern "democracies", here in Australia RCD's legislation has been constantly changing from: no RCD's, to owner onus RCD's, to at least an overall RCD but with exemptions for refrigerators & freezers and life support systems to no exemptions to mandatory RCD's on all circuits and wired in from behind the main distribution panel so home owners cannot easily swap them out for just breakers or fuses. We had a tragic electrocution case in Western Australia two years ago where a little girl has suffered permanent brain damage (as well as other injuries) when the neutral wire to the house failed, because the neutrals and earths all come together on the main distribution panel using the MEN (multiple earth neutral) system the any RCD's (if fitted, I don't know if there were any) would not have detected the acive-neutral imbalance) The little girl was electrocuted outside the house touching a garden tap whilst standing on wet earth, obviously the wet earth presented a low enough path back to where ever the neutral was bonded to earth.

Today with so many SMPS in everything should be type A everywhere Sad only few manufacturers have them in catalog

I love how Tom is like the gold standard of electrician KZfaqrs that everyone is compared to

It took me a minute to realize that in the UK a lot of people have heated showers and that's why your showers use electricity😂

wow, those things are complicated, but cool. here we don't have any residual current breaker, only 80A overload, and that's that.

Thumbs-up to videos that feature electrical/electronic products with black, sooty skid marks! Especially if it looks like bits and pieces ended up in the next county! 💥

Ah but, did it trip, or was it pushed? Well, I've learned something today, and I'll bear that in mind if I encounter the same kind of issue.

Some clever engineering in RCD's I took apart a Wylex RCD as it failed RCD testing on my Kewtech KT65DL MFT, the sense coil was made of really fine layers of what looked like chromium leaves of flat wrapped material, strange...and it broke apart really easily.Still never figured out what it was lol. But it had similar minimal electronics like that Hager, just a few diodes and a resistor. Clever stuff! anyway, I replaced the wylex RCD and it tested out fine.

You are lucky in the UK that almost all the residential breakers are Standardized, here in the US there’s so many brands and profiles. Both of our subpanels are standard Square D but the main panel is an FPE (Federal Pacific Electric) and the breakers are outrageously expensive, it’s like $150 for a 20 amp breaker, although they do trip like they should. The electrician that we hired to wire the kitchen and some of the basement wasn’t the sharpest knife in the drawer, he put an outlet in the basement on the same circuit as the outlet for the microwave, and we have a very powerful microwave, it’s more powerful than most microwaves on the market, but I’ve found that if you run the microwave and a vacuum cleaner in the basement then the breaker will trip.

Had one RCD do odd things. Once it had a 20-30A load in it if you just switched on a socket with any appliance attached it would trip. It would pass an RCD test which is usually ramp tested. Got to the point of testing with a static leakage with a homebuilt device that could switch in 5mA at a time. At 35mA it still hadn't tripped. Usually you'd expect them at around 20mA to have gone. RCD swapped and never had a problem again since. No other leakage was found on the system past the background few mA - checked with a clamp leakage tester.

Holy crap! I don't think I'll move to Europe any time soon! :)

I've had my share of nuisance tripping on RCDs. Interestingly I've used that very same RCD, it's actually fairly good quality (compared to the really cheap stuff), but still quite a bit cheaper than the really high end stuff (ABB). I discovered that modern appliances typically have surge arrestors and EMI filtering stuff in them that causes a small leakage to earth. If you have enough such appliances on an RCD, you get to the point where it's right on the brink. During times when we get rotational power cuts (known as load-shedding), it is quite common for the RCD to trip when the power returns after an outage. Backup inverters that have their own TN bonding relay also open the TN bond to test the relay (this is required by grid codes in many countries), and the act of removing the TN bond temporarily as well as passing a small DC test current through it all adds up to very frustrating and intermittent RCD tripping. That is when I learned about the various types of RCDs. There is type-AC (the one in this video) which is your traditional type, only really sensitive to AC leakage currents. Then there is type-A, which is better. Then there is a subset of type-A that has a small delay built in to avoid nuisance tripping on transients. ABB calls theirs "type APR", Gewiss calls it type IR (impulse resistant), Hager calls it HI (high immunity). These are quite a bit more expensive than a plain type-A, but must more affordable compared to what comes next. The next step up is type-F, and then type-B. These things are practically unaffordable. In my house I have the loads split over 2 RCDs (roughly 7mA standing loss over each one), and one of those RCDs (the one feeding computers and other switch mode supplies, things that traditionally have higher standing leakages) is an ABB type-APR.

I've had problems with RCDs tripping in circuits which use half wave rectification or poll the mains to use only one half of the sine wave. This results in the detector coil becoming magnetised rendering it more sensitive to leakage currents. With the Electric vehicle charger I first had this problem with we found that when thr battery reached 50% charge the charger halved its output power by only drawing power from the mains on the positive going side of the waveform. After about 15-20 minutes the RCD tripped and we measured the leakage current at 5mA, pretty much what was leaking from the whole house.

you only need to test rcd's six monthly, i always find it is a good time to test them when the clocks change.

Interesting, thank you. Would the signal from the transformer be full-wave rectified before being applied to the solenoid? That would seem sensible if the residual magnetism in the solenoid has a specific polarity, as I presume it does. With full-wave rectification, why should tripping be more sensitive to one phase than the other? If half-wave rectification, why should it trip at all on the other phase? If no rectification, how does it work?

Would be interesting to do an overload test! Apparently they become unbalanced and more sensitive when overloaded which would make an split load boards safer for overloads.

Cumulative earth leakage via multiple points will do it every time, particularly resistive heating units like cookers, ovens, hot water units. In Australia we initially were allowed to hang every circuit on one RCB, not anymore, the last regs I saw it was a maximum of 3 final circuits on one unit. Fixed hard wired devices such as cookers, hot water heaters with current rating over 20 Amps were not required to be Earth leakage protected as it was finally released the major risk of earth fault shock was from hand held or portable equipment exposed to abuse or damage. Lighting circuits are required to be protected as they are often fiddled with by people trying to fit ES bulbs into BC sockets and so on.

Nice the double winding thru the sense coil ring. But would it not easier (and uses less copper) to double the sense wiring?

Hi mate, you don't have to populate a C/U in order of load anymore. The thickness of the busbar renders that unnecessary. For sure the installer should have split the showers between the RCDs but it doesn't surprise me that the RCD is fine. It's quite new and an AC type. It's far more likely that the issue is related to items plugged in to the kitchen circuit. If he had tested properly no doubt he would have found the problem. Love your videos Clive!

that's a cool tester i didn't know existed neither i think i need it but i sure want it

Clives the kinda guy who could be making everything up as he goes along and you would still believe him.

TN-C and TN-C-S aren't novelties. In Germany it was permitted until 1973 (in East-Germany until 1990) to have a PEN conductor in final circuits, then this was changed that the PEN must at least have a size of 10mm² (copper) or 16mm² (aluminium). In the last version of the VDE 0100 were this was permitted, from the year 1969, the PEN should be connected to the earth-terminal of the outlet and from there a wire bridge connection to the neutral terminal of the outlet. The system is perfectly safe as long as there is no PEN breakage. This condition is a massive problem, because metal housings could become live at mains voltage. The most common systems here are TN-C-S and TT. But several DNO are now converting their TT-grid into TN-C-S, which is actually no problem for them. In case of this picture I can clearly determine how old this is, the combination black and green/yellow in a two core cable was only available between 1965 and 68: images.gutefrage.net/media/fragen/bilder/steckdose-anschliessen-mit-zwei-kabel/0_big.jpg?v=1544095332643 The outlet itself is not original, it was changed in the 1990s when screwless terminals for outlets came up. And actually it looks like someone didn't bother to install a box into the hole...looks like remnants of a hollow wall box are in there...

I almost thought you were going to say rccb as in the ones on airplanes. They might have a switching power supply that the coupling capacitor from the low side to ground is on its way out to cause it to trip.

6:38 I don't test it that regularly because you have to set the time on the oven again, and the time on my alarm clock .....

Interesting. We have an issue here where each level of the house has its own panel with RCD's on each board. There are times where we might get a trip in the basement RCD when lightning hits real close but the other upper two levels do not trip. Outside there is an entry pedestal fed from the meter which is street side some 30 meters away. In this pedestal is a breaker box equipped with 4 MOV's and safety breakers. Indicators on the MOV's do not indicate any partial or total failure. Still we have that basement tripping, weird. Back in the states we had outlets in the bathrooms which were equipped with internal RCD circuits. These would feed through to the other bathrooms providing protection. The kitchens as well have one outlet that feeds several others. The fun thing is while talking on a handheld commercial two way radio I could easily trip the RCD as I passed it while keying the radio. Would tweark off anyone using the outlets, tis not good to piss off the better half, one could wind up with brain damage and not from the RF energy of the radio......

Interesting, fitted thousands of these, never seen inside one before

All the Queen's horses and all the Queen's men couldn't put RCD back together again.

I remember being on a jobsite with a temporary power board... essentially a junction box screwed to a wooden stand in the field. I saw a low level labourer there leaning on the board. His job was to hold the breaker on. Safety first!

I'm not convinced that trip is being held by residual magnetism but is in fact hed by an 'over centre' spring akin to kettle trip bimetallic doodah arrangements.

Oh, wow. I just replaced one of these in my house. The RCD kept tripping randomly for a few years, but not too often. Then on the last occasion, it wouldn't reset, as it wasn't holding the contacts together tightly enough. I strongly suspect I still have leakage current somewhere, as the breaker for the top floor ring main also seems to trip sometimes. I don't have a proper clamp meter that will measure low enough, though, and don't really want to fork out £70 just for that one test. So I was going to suggest (to Clive) about maybe using the current transformer from the RCD to build a cheap leakage tester? Obviously it shouldn't be used for doing proper safety checks, but it could be made fairly accurate once calibrated against a multimeter. Or, I guess I could just break the connection from the ring main to the breaker, then shove the cheap "20 Amp" rated multimeter in series, but I'd rather not. lol

Definite signs of sadness

On that Screwfix screenshot the top two are Type AC, the bottom two Type A.

You have the same voltage in Britain as we have in Germany, about 230-240V. But your breakers are much larger than ours! I've got a bunch of 16A breakers, often for only a few sockets, and then also 10A and even 6A for the bathroom socket. The biggest breaker in my flat is that for the electric stove/oven at 25A. The sockets for the washing machine and the dish washer in the kitchen are also 16A each. Other circuits enclose a whole number of sockets on one 16A breaker. I find it interesting that you have such high values there.

I wonder if that small loop of "long wire" or the coil is responsible for these things tripping due to radio waves? I am a HAM radio operator and when I use my UHF radio (around 430-440 MHz), the shower trip flips every time. I have seen lots of posts online about smart meters tripping the RDC/GFCI. They usually send on mobile phone frequencies (around double that of UHF). I see absolutely NO RF shielding anywhere. It would be awesome to test one of those close to a cell phone to see if it trips. I bet it does. My appologies if you have already done a video about this as I am new to your channel. Awesome work! Respect - Gerald Magill B.Eng. in Electrical Engineering (Hons).

Have you heard about the TV in Montgomeryshire causing the DSL to not function correctly? Would love to see a video about it on your channel!

Was this RCD damaged by overcurrent? After tearing it into a million bits the answer is NO... Well thank goodness it wasn't damaged!!! Then Clive says "This RCD is not going back together again..." Yeah... Ya' think? LOL 😁 Anyway, we don't have that kind of electrical system in the U.S. I find these teardowns very interesting. Thanks Clive for showing us that.

Working at a power/ waterplant. We have some very cool relics at work wood pipe, Flow meters. Generators Fairbanks- morse 1930, 1947, 1955, 1967, 1989, and 2 1992 generators. Museum quality all off them fully functional. The wood pipe blows my mind if ya can picture a 4x4 post with a hole drilled out. 42 inches long with 6 inch slip in 😁 tip.

Residual offset current. This was a problem with teleprinter (Creed 444) receive electromagnets, driven by bespoke (RAF) magnet drivers, fairly late in the life of such magnificent machines . . . which meant that the problem became apparent after a couple of years, was recognised for what it was and the ball was quickly passed between the manufacturer (Plessey who had bought up Creed & Co), BT and 38Grp RAF. Believe me, a Teleprinter that has been sat on standby which fails to register signal reversals on the line is not a great deal of use to either man or beast.

Hi Clive do you run a Q&A forum. I have a question about what the life is of an RCD. Are they meant to last? Or should they be replaced every so often

10:38 I think they brake the test circut becaus it would bypas the mainswitch. The test works like Input1->testButton->resistor->littleBrakeContact->Output2 (or another order). Whith means it is not possible to power the output accidential over it with no Protection. Yes there exist Locks and Seals for RCDs for working. Nerver used one. Greatings from Germany, sorry for bad english.

We aren't allowed to deploy RCDs here in Oz. New regs require new installs must have RCBOs. We also don't do ring-mains in Australia.

Thermographic inspection on DBs can be quite revealing, we've had dodgy MCBs show up using this

We need more Melty Moments videos.

I'm a bit surprised by how much everyone in UK cares about electrical safety, even in residential buildings. Looking at those well-organised fuseboards feels odd. My soviet-built hruschyovka (just like most others) doesn't even have earth connections inside except for the bathroom socket; there are only 2 breakers for the whole apartment - one 16A switches the single hall socket and bathroom lights, the other 32A covers everything else; the kitchen lights are wired incorrectly - switches are on the neutral wires so the lightbulb sockets are always live even when switches are off, got zapped once thinking it was safe The main fusebox in the entryway is an absolute CLUSTERFCK of loose cables and unlabeled breakers, with about a third of all breakers just hanging in the air. Some connected wires have a ~1cm of bare copper between the breaker and insulation, meaning that someone can easily touch it themself or make it contact the metal case when reaching for a specific breaker. My internet provider has some equipment on the roof that is connected with a 2A breaker placed in the depths of this mess. After even a brief power outage someone has to reach through the loose wires and switch off, wait, then switch on the breaker to re-enable the internet for everyone. No wonder a fusebox in a neighbouring entryway went kaboom a few days ago, almost starting a fire. I guess there are some bad electricians and messy fuseboxes in every country, but an installation you or Nagy would call horrible would probably be "not so bad" in comparison to stuff i've seen here in Russia

Incomer fuse value is important to note

Could that "smooshed up " wire have been inducing a magnetic field in the sense coil, as it was twisted into a loop and was right next to it?

Here in USA brown and blue are low voltage DC. At least industrial purposes. Also if all Great Britain is 240 volts,What is the neutral for? Thanks for explaining so much stuff Big Clive. Have a marvelous day!

All my kitchen sockets are on the same RCD, the cooker is gas however and that's ALL that RCD does.

Tiny leaks from each appliance will add up to trip value. Especially for wet stuff i.e cooker elements and shower elements on the same rcd.

Was that a wylex breaker that was on the recall a few years back?

Take it to bits, Get ma spudger, One moment, please. All perfect toolbox stickers! Get it to it! Lol.

If you put low voltage dc on the sense coil, will the core and the spot welded wires act like a saturable reactor?

There may be a permanent magnet at the other end of the core and when the coil energises it may cancel it out?

Regular RCD testing recommendation is once every 6 months according to 18th edition (used to be 3 months). Max allowed trip time for 1x is 300ms so your 40ms was ok. Max allowed trip time is 40ms at 5x I^n