“The more you complicate the plumbing, the easier it is to stop up the drain” -Scotty

I chuckled at the "JW here" impersonation, love it.

Very interesting that the first sign of a problem was nuisance tripping. I became involved with an installation where the main board was loaded with breakers of the same brand. It started with one nuisance tripping so I replaced it. After the third failure within two weeks the whole lot disappeared into the round filing cabinet. I replaced them all with Clipsal breakers and no problems since. Luckily none of the breakers in this installation moved on to the pyrotechnic stage. I have been using Clipsal breakers for a long time now and I have never had a problem. I love your work Clive, thank you for the post mortem.

Clive, when you do eventually drill/cut/burn your hands on camera enough to require a hospital trip, remember to take your camera so you can continue to document the event. :)

It's interesting that some RCBOs have the extra earth wire for sensitivity for loss of earth and Reverse polarity tripping and others do not. I have used Hager three phase disruption gear and never opened up an RCBO, too expensive with top brands when still working. Really interesting to watch and hear Clive show about the workings and it's components.

When a circuit breaker becomes a fusible link. At the right voltage and current, _anything_ can be a fusible link. Life goal: Never be that thing.

So I learned two things from this video: 1. The breaker clip thing, and 2. Drilling out rivets. I have always punched them out with a hammer, but drilling them out is so much easier. Thanks Clive!

The way you went through the fault finding route reminds me of the tv program called "Air crash investigations". 😀

That's something that used to happen where i worked, peiople would keep resetting the breaker thinking it would clear the fault. I think that's what happened there, the continual resetting has caused some of the blackening, the rcd trip coil has been powered for a long time and that has overheated causing the bobbin to melt, seizing the plunger. I can't remember where the neutral runs to get to the other end, my guess that it is clos enough to the live and flashed over causing the majority of the blackening and 'sputtering' of the copper. We didn't like Hager, crabtree was preferred, you could get rcd modules to convert a mcb to rcbo, neutral didn't pass through the mcb section.

I just want to say thank you for these videos, I may not be into electronics (although I've learned a few interesting things from these vids), but I find these videos along side some smooth jazz or lounge music make for the perfect background noise while studying, with the music combined with your calm voice and the various clicks and whirs of your equipment.

Awesome teardown. Thanks. Nowadays in Australia where I live the newer RCDs always have an overload breaker built in and they are no larger than a normal circuit breaker. We remove RCD main switches because any ground fault cuts *all* the power to the house which is very inconvenient. So we put RCDs on individual circuits instead. We also delibretally leave some circuits without RCD protection. Oven, Air conditioner and usually one power circuit.

In fairness, once you've welded the contacts, I find that "blowing up the RCD circuit" is pretty low on your worries list.

I've never seen so much magic smoke residue in one small component in my life.

Just what we see in the Southern US when we get a direct lightning strike to the mains or load. BOOM! I tried various lightning protection strategies, but the problem finally stopped when I built a large metal shed on the hill above the house.

I like when you share extra knowledge while opening circuits or other.

Clive's best line, (opens up the breaker) oh that's not happy is it.

It is interesting to see how the test circuit creates the imbalance to trip the circuit when tested. I had assumed (for no valid reason !) that the test button caused a current to earth that was detected and tripped the RCB. However that is not what happens - the test button causes the test current to bypass one side of the sensing coil thus creating an unbalance. However the test current is still flowing from Live to Neutral not to earth hence testing a downstream RCD does not trip upstream RCDs as they see the test current as balanced. Very clever when you realise.

I usually lock the whole sub panel box been bitten to many times by people getting home and turning breakers back on when I'm working on the system...

Me and my dad only use these in domestic settings. There's an amusement arcade our landlord owns about 10 yards round the corner from our house & the distribution board is a split load board for each section. There's 3 phases coming in with a split load board on each, powering about 6 areas of the arcade floor. There's about 80A load on each split load RCD in total (they're 100A RCDs, 2 per board) and there's 2 Hager boards there (dad has always seen them as reputable and no issues to this day really). There's a Proteus board there as well (newer metal enclosed one because of the 17th edition 2015 update). If this happens more regularly with hager switch gear, i might consider switching them. All the stuff in our home is MK or Schneider luckily.

Great analysis. I had some experiences of my own with welded contacts in an industrial design project, but the contacts were those of heavy-duty relays. I learned a few things. It's a scary failure mode, particularly if there's nothing else downstream in the way of protective circuitry, fuses, etc., and the machinery in question poses a potentially major fire hazard. In our case there were protective circuits but their job was... to switch off the relay. The one with the welded contacts. :-/ Damn good thing the problem emerged in the prototype stage. The relay was SUPPOSED to be so over-rated for the purpose that no such failure was even possible. Got it sorted out in the end and the result was nice and bulletproof. Fixed it three different ways, actually. The design has remained in use now for 25 years in thousands of machines with zero failures of which I am aware.

Hi Clive :) In France with our breakers if you can put a lock on a close one it's no problem. the lever on the front isn't directly driving the internals, it's only an indicator. I already had some circuits breaking and all levers where up so i had to find the one tripped and close it by pulling down and up the lever. So if it's a sensitive equipment that you don't want people to bring it up if there is a fault you can also lock it up and if it trips the breaker people without the key wont be able to do any action on it. (it's a clever idea but not sure if all breakers has the same internal behavior) tested with Hager / Legrand)

love the smell of burnt breakers early in the morning and terrified late at night !

Hager had big recall a year or so ago. From memory it was MCB's not RCBO's. Interesting video, especially as I have fitted Hager stuff for the last 20 years. On the whole they are reliable though in my experience.

The welded contacts remind me of a time our old (1999) 10kVA UPS ran until all three battery cabinets were depleted. Once we got the mains back up, we had to run on bypass until the vendor could come out to give it the old crowbar and hammer fix.

I think I agree with you, Clive: this doesn't seem to be a "one-time cause" catastrophic failure. Many, repeated trips with an inductive load is a good guess. Poor thing killed itself trying to open the contacts.

Its very common for old CRT arcade machines to leak a small amount of current to earth in operation, so when you have a large number of them, they like to randomly trip RCDs, even type C, we've done alot of experimenting with it and it definitely is the monitors

@6:38 When Clive said, "oh dear" - and you don't hear that often from him - you know somethings fu****up

Thats a little scary when the contacts weld closed

I used to work at Bulldog electric in Detroit, in the lab where we UL tested circuit breakers and starters. Lots of burn marks on the wall, and good fun.

Now we're all waiting for the next video of you repairing that thing :D

I would call this type of incident a "Hard Failure" As in...when the fault trips the unit but the contacts have welded together.

I innadvertantly back powered one of these whilst using a single circuit from the previous install whilst commissioning the new set up with much the same effect. I put the power on and heard a buzz for about ten or fifteen seconds (the time it took me to kill the power) and saw that is let the smoke out of the RCBO. Own fault and own money to replace the failed part. £25 lesson, well learned.

That was definitely turned into charcoal, must have made a nice bang when it went... :P

Looked like someone discharged a large cap bank, damn that thing is cooked. Never thought they can blow up this bad just from normal use.

Breaker locks where one of the best investments I ever made.

I just replaced a Hager 10A RCBO 2 pole single width that failed to trip with the test button after only a couple of years. It would buzz and start smoking within a second of holding the button but not trip. I tore it down and discovered they had incorporated the RCD and overload coils in the one aluminium package. Some clever engineering in the linkage was supposed to trip the lever to half position to indicate an RCD fault and full off to indicated an overload in order to diagnose what had actually tripped it. In reality, the linkage ended up binding and preventing a trip on either RCD or overload. I could not see any thermal trip strip in there. The resistor for the RCD test was still intact and measured 3250 Ohms so at 250V would draw 77mA and dissipate nearly 20W. No wonder it smoked after less than a second. It seems they tried to get a little too clever for the room they had to play with. It has tainted my faith in Hager products now.

C3 also limits inrush current to the thyristor trigger. We had problems with that issue, especially on higher power devices (6 to 8 inch diameter chips) and, in an extreme case, the Silicon can actually splinter off the top surface, in a saucer shape, taking the gate contact with it. The solutions to the problem included multiple trigger contacts on the Silicon surface, plus careful Silicon doping design, and external inrush protection components, such as that cap, C3.

Heat the beans Martha, it's toast.

I've trained to be an Electrician, my guess is IF the Breaker Contacts welded shut due to a dead short somewhere in the Branch Circuit its supposed to be protecting, the next thing to trip would be the Mains Breaker protecting the entire Distribution Panel (hopefully before the Branch Circuit wiring caught fire from WAY too much Current flowing through it). Tripping the Mains Breaker would also have the fun side effect of killing power to the entire building...

Daymn, that's so smoked I can smell it from here! (Not completely joking either, I know that smell well enough that I can 'almost' smell it)

Mike was playing with his destruct-o-tron again ;) "Oops" :)

That's a neat lock out.

Scottish AvE!!! Yessss!!!!! Love ur in depth videos and that center punch u were using to pry the breaker apart looks smart too!

Clive, The name RCBO always made sense to me because I called normal (human safety) RCDs RCCB - Residual current circuit breakers which I believe is the more specific term, you can have other type of RCDs I think.

Had to be a Voltage back "SURGE" I found, over years GFI, Outlet devices, with MOV, "Metal Oxide Varisters" really, "Draw" the surge to circuit boards. Electrician for 45 years.

I would love to see the insides of an MCCB sometime soon. Even better, a breaking up of an ACB. They seem to have the same technology as a satalite nowadays.

The casing contained the shrapnel very well possibly preventing it catching fire?

damn, these appear to be the same model I use at work. Reckon this is an isolated issue, or something I should consider getting rid of, and finding a different model/brand replacement for? In my setup, these are connected to modern monitors, no degaussing coils.

This is an expensive little device, I had to think few times to have more than one installed in my house but safety is the most important aspect to be considered here.

The generic device is RCD - Residual Current Device There are two varieties of RCD: RCCB - Residual Current Circuit Breaker RCBO - Residual Current Breaker with Overcurrent protection However, RCBO's are newer/less common than RCCB's, so it became usual to refer to an RCCB as an RCD when there was only one type of RCD in general circulation. So now we have RCD and RCBO.

Had a similar situation with a mem3 rcbo, like the Hagar you've got it has vent holes on the side. The energy vented into the rcbos next to it via the vent holes and damaged those also. Consequently we no longer use mem3 due to this design flaw. 😀

"JW Here.." Best part :). Good grief, What a mess!! Is this from a reputable manufacturer?

by 6:50, that had to be a direct or nearby lightning strike with huge voltage and surge currents. I'm betting it arced from the wire passing through sense coil to the control circuit and up stream as it tripped. I've seen many GFCI outlets look the same way from direct power line/pole strikes ( above ground electric here) lost random devices all over my own house in the past, it hit the whole street of people randomly killing devices also. I'm betting the same thing occurred on "John Ward's" video you linked, only it didn't trip catastrophically, only damaged the control circuit and went kaboom, when tested.... which is exactly why they say "test weekly" on all the GFCI's in USA. the one you had looked to be obliterated instantly, Johns looked to be a death trap that could have electrocuted someone!

Definitely gone with a nice bang 👍👍

Yay a JW mention! Thanks for watching.

Makes me wonder about the *2-pole* 1-module RCBOs available from some manufacturers (although to be fair, those are only rated to break 6kA at most). If the test resistor contributed to the bang, then using a fusible type should help. Adding a fuse in series with the solenoid (possibly a thermal fuse mounted to the coil) could also improve the situation (although it would have to be chosen carefully to avoid blowing when it shouldn't, which would be nasty in its own right)… I suppose the welded contact is bad enough on its own, though.

Oh that isn't happy!

Sophisticated electrian slang "totally exploded" 😂

Yeah, our family ran a pinball machine (and some other arcades) hall back in the -70 and -80’s and i remember we had huge problems with power, nothing a screwdriver fuse couldnt fix!

I think I have a board full of these protecting my house...

Use the Force, Big Clive! :P

Grrrrr.......LOTO......pain in the bum. Interesting video. I knew there was degaussing coils in old crt's but not how they worked, though the more I think on how crt's work it does make sense. Still, learned something new. Nice And that breaker is properly cooked !!....

I wonder what happens to the IC when the fault current is so large? Could the transformer-coupled voltage (sense voltage) be large enough to damage the IC and cause the triac to stay on until "bang"?

Tripping and not catching reminds me of the one breaker in my old apartment...which controlled 2 bedrooms, 1 bathroom, 1 hallway, and half the livingroom.

In your discussion of CRTs and degaussing coils, you mentioned a temperature-dependent resistor that would limit the current when it got hot... I've seen super-cheap CRT driver circuits that used a small *light bulb* for that purpose, believe it or not. Works great until years later when the light bulb filament burns out...

You mentioned that it came from an arcade....well, most arcade games use switch mode power supplies (basically like home computers) and older machines use regular power supplies with transformers. Switch mode power supplies usually draw a very brief but extremely high current on power up to charge the mains capacitors...and of course transformers also have inrush, but of an inductive nature. Having worked on arcade games, and seeing how arcades operate, here is my theory on why this burned up: They used that breaker to turn ALL of the games (and/or lighting) on and off at the same time, instead of using the individual circuits. The combination of capacitive inrush, combined with inductive inrush (and resulting capacitive/inductive currents creating resonate overvoltages) finally hit critical mass and blew it up. Even a standard Non-RCD breaker's contacts will fail with such abuse. I have had to replace many breakers in arcades for this very reason. If the viewer who sent this to you is reading this: Tell the arcade to change their daily routine or it WILL happen again.

Addition to the electrical lexicon "Plungery" :)

This is a good example of over thinking a simple fuse

I am happy with that lock out equipment. I work allot with lockout tagout on work because of safety.

I suppose all you would need for overcurrent protection alone would be a shunt resistor and a spring loaded relay. The coil of the relay with the shunt resistor across it, 'live in' on one side of the switched output, then looped back to the coil, 'live out' on the other side of the coil. If too much current is drawn, enough current will flow around the shunt that it will trigger the relay.

But lockout tagout takes all the excitement out. Health and safety gone mad.

I have had this exact problem on a high in rush load circuit that a breaker was used as a on off switch for. Repeated use leads to it over time weakening the breaker until it eventually welds itself like this. The solution was to put the load on a MDU that turned on in a staggered way

Kind of gives a new meaning to exploded view

That plunger would have been buzzing so fast just before this blew.

Contacts welding together sounds like the worst way a breaker could fail.

It was so much simpler in bygone days when you could just put a penny behind the glass plug fuse. And we really did do that.

breaker idea: get a slightly beefier SCR on that RCD output, and on trip, just short the output of the breaker. that way you can simplify the mechanism since the short circuit will fire the overcurrent solenoid, and it might even be safer since it practically instantly crowbars the output to / close to 0V with no mechanical delays. although, I'm guessing breaker manufacturers know what they're doing and an SCR that could survive that load would be impractical

The big unknown. What's the history of the device? Constant resetting on a fault? Lightning strike? Wired up wrong? And the device, while it did blow up, stayed intact, nor did it catch fire. But then any device being subjected to fault currents tends to leave black marks somewhere. I've seen the results of a whole switch panel blowing up. Just a hollow shell left with copper busbars splattered everywhere. Same with a lightning strike on a house where it was a total rewire due to the cables melting together. Faults happen.

Great video thanks Clive. I'm now wondering about kA ratings: breaking current. (I'm not a leccy but have to deal with these things for my sins.) I would expect 6kA to handle virtually all domestic and some industrial installs. But you mentioned this one is Type C. Does that mean the kA rating is down to a lower power factor, or is it just that the instant trip level is higher? Food for thought. But not too much. Tonight's bin night and I like to ration my excitement.

I would suggest the power lines were subject to a lightning strike and the resultant surge has destroyed the breaker.

Great tear down and expaination of what went wrong, maybe the simpler circuit would be better in the long run.

Isn't that bit that got welded together kind of a fatal flaw? obviously it will go bang, but before it does there is a very brief moment it seems where whatever is causing it to trigger, will still be happening, with all its possible consequences. Or am I missing something?

I think Hager would have liked it to examine... 😕 Being type "c" , would it not actually have been getting quite a lot of surge & "tolerating" it to the point of failure... would a "b" breaker of a higher current rating not been better Clive ? I'm starting to have second-thoughts about going the RCBO route for my new CU... 😒

Thanks for sharing 😀👍 Interesting fault

Hi Clive , Great videos thank you! What camera do you use? I have to make some training videos, your seems to have good features.

it compares current flow on the "hot" and "neutral" wires, so if the current flow out the hot and back via the neutral are not 99.x% equal? it TRIPS, meaning that user device is shorted/has a "ground fault" that is assuming the control circuit isn't "dead" from other comments mentioning lighting and surges

Bigclivedotcom, please correct me if I'm wrong well anyone for that matter. Too me it looked as if that tiny black wire that was broken off right when he split the shell looked like it went to the Spark Arrester Spike's? What I'm getting at is that if that wire failed due to an insufficient conducter, wouldn't that have cause the Arching to occur on the single- pole latching switch? Followed by it being welded together and the fault unable to be broken?

In Australia some Hager RCD have been recalled. I wonder whether this is one of the models?

I have had issues with these and your comment about these using power (albeit not a great amount) they do get warm.and thanks to misinterpretation of the good old 18th edition our local authority are fitting these as a matter of course.And after a year even they admit they are seeing issues on "some instillations" I was wondering if you have started seeing any issues ?

Wow, great video as always

Great autopsy, some people think resetting; is holding it in the on position for several seconds, even though the mechanism is trying to switch off. Thankfully standards, and better training/certification for electrical installers has greatly improved since my first foray into domestic installations circa 1970's. But idiots do breed ( rather well, if truth be told). My best story of attending a customer, was being called to a lady's house, who complained that her new TV picture was smaller than it should be ( Vacuum set), her TV supplier said it was fine. Within a few seconds, the cause was obvious, the surface socket of round pin 5 amp type, had been wired directly to a 16 amp fuse with "Bell Wire " having a current rating of maybe 3 amp max). Lucky, the lady didn't own a vacuum cleaner or electric fire ( this was the only socket in the room) or there would have been a lovely burnt pattern under the wallpaperd wire. So, a new 13amp socket, wired in 2.5 T/E channels with steel capping, and she had a nice full screen picture. In asking who had installed the unsatisfactory item, she said it was a friend of the family who worked for the local electricity supply company ( MEB - Midlands Electricity Board)!!!, Asking around, it transpires that this was true, but his job was digging holes!!!.

hope they fixed the issue in the circuit it was feeding, something clearly wrong there. then again maybe a lightning surge harmed the device and made it randomly trip.. afterthought, maybe they used the thing as a "daily power switch" which breakers are not meant for! I've seen that kill many.

They're lucky they didn't have an actual fire! I know the breaker housings are supposed to be flame retardant, but what about the location of the fault?

So, to prevent electric shock, when a ground fault is detected, melt down the entire breaker panel. When the copper bus bars melt, power is lost to all circuits terminating in the panel. Rendering all circuits safe. I never thought of those bus bars as fusible links.

I've seen some contactors , fuses , triacs and thyristor blow but never actually a RCD / GFI DR ( PT_PT Disjuntor Residual ) blowing this violent. That must be some on / off events, arc's passing enought energy to weld the joints. Must be some sort of surge load such inductive load ( pump motor) and the thyristor is not snubbered properly for that appliance, even that has the right class

I used to have hair clippers that would almost always pop the GFI in my bathroom when I switched them off. The device was "double-insulated" (no ground/earth prong) but had a polarized plug. I guess it was a residual magnetic field collapsing and inducing current over the neutral line?

Hi Clive, your cough/raspy throat might well be symptoms of pollen allergy. 'Tis the seaon, after all. Birch pollen have been rampant this year, the last few weeks. Consult a doctor, an antihistaminicum can help a lot.

i would hazard the welded contact meant the solenoid trip circuit was running full time when it is only rated to for a very small duty cycle as it kills it's own supply. The solenoid heated up , melted wires and caused all manner of secondary smoke.

Very scary to use those breaker failed to trip

Would be interested to know what the earth fault impedance was of the circuit this was connected too