The magnetic effects of fault conditions are fascinating. Here they're used to induce a current and trip a breaker. I used to build distribution boards with big copper busbars in them. We had to put supports every 300mm because, under certain fault conditions, the opposing magnetic fields could "cause the bars to slap together like rubber, which wouldn't be good for anyone nearby" as my boss explained it to me.

Many EVs only support single-phase charging (typically 32A) , so the burnt pole may be the neutral - Rolec had lots of issues with burnt neutral terminals on home charging units. My guess is that the spring being at the end furthest from the burnt contact means there was reduced contact pressure

One megawatt chargers for trucks: "huge potential for exciting electrical incidents." I see what you did there.

About the lack of active circuity: A good RCD is supposed to trip on the current difference regardless of the operating voltage. So the tripping trigger has to be powered by the pickup coil only. This makes it very delicate and expensive. In the cheap RCD the current from the pickup coil is fed to the thyristor which uses the main voltage to activate the electromagnet of the tripping mechanism. This makes the mechanism much cheaper but won't work without proper voltage. This type of RCD is not allowed in my country.

Dear Bigclive I also opend up an older RCD (already a DC Pulse capable type, same logo as yours) which had a similar PCB inside with Diodes and Tantalum capacitor, but there the sensing winding on the maintransformer had a connection in the middle of the sense winding, which was connected to the minus of the releaser winding. The 2 diodes formed a half bridge rectifier, for positive and inverted negative pulses to charge up the capacitor with a positive voltage each and it was connected to the positive connection of the releasing coil. The capacitors negative side had a connection to the minus of the releasing coil too. The releasing coil weakens the magnetic field of the little permanent magnetic pill. The magnet, which sits on top of the coil when the contacts are closed, and holds the mechanism, separates from the coil and the RCD will trip, if any pulses charge up the capacitor. Regarding the burnt contact you have to keep in mind that this RCBO sits in a housing where moisture in the air is one topic, due to the fact that the charging post usually sits in this box in ice cold and sunny hot weather, unclimated. On top of this you have a high current load, which will heat up the wires with every charged car. As mentioned in annother comment some cars only use a single phase, so the wires for phase1 and neutral will get the highest tear and wear. Together with a maybe weak torque while mounting the cable into this cage clamp the cable corrosion can start in the clamp, with more oxidation on every charging cycle, and therefore it gets everytime a little bit hotter the more the oxidation advances. Furthermore there is annother topic: The contact in the RCBO has a silver coating which can get the black corrosion on it. This black silveroxide has a high resistance. In a stairway timer light switch the corrosion is pushed to the side or burnt away with every triggering and release. But how often is a RCBO contact opened to have a cleaning effect on the oxidation layer?

Anyone else notice the fantastic sound quality. It's like you're sitting beside me big Clive

Yes, they are tantalum smd capacitors. The bar marks the positive end, because, why not do the total opposite to electrolytic caps, where it marks the negative ?!

If the actuator pushes on the far right end of that shaft, and the contact on the far left is messed up, my gut instinct is the shaft is twisting a but too much and not applying sufficient force to the contacts. Smells a lot like a basic design flaw to me.

If the gardener can kill the protective housing, I expect the whole device is built to a very low price, to compensate for the price of installation.

Clive, great video! It's a three phase unit, but many cars only use singe phase so L1 gets most of the work to do.

Very interesting Clive. Thanks for the video, love the way that the trip mechanism works. Bet that solution did not come to mind overnight. As for the failure of the end contact, I would guess that contact pressure on the end contact is not high enough and it runs hot. But the video stimulated my thinking about a problem I have to solve at work and now I have an answer for the folks tomorrow. We work with variable frequency motor drives and ground fault detection on the load side is tricky as the fault current on the ac side of the vfd is dc due to the nature of the conversion process, when a ground fault occurs on the output of the vfd. So a core balance does not work in that situation. But, a transformer type core with two winding's will work, because the output voltage from the measurement coil changes when dc current magnetizes the core. Is what we get up and go to work for in the morning, dealing these interesting and stimulating works tasks to deal with. And then sharing the experience with others, like you and other creators on YT do. Kind regards, D

With the activator mechanism on the right, i wonder if there was enough twist in the bar so the left contact isn't as tight as the others.

Interesting. AC type RCDs are forbidden in Germany because they don't detect any DC faults. That's why it failed here. You actually should use a type B RCD for charging stations. Unfortunately B type 40A/30mA costs around 400€ compared to A type 40A/30mA which costs around 30€

Good to see that your hand is healing up nicely!

The little trip plate is surprisingly similar in design and function to the trigger and hammer sear in a firearm's trigger group: a very small, weak motion in one direction unlatches a catch that allows a much larger and more forceful motion in another direction. Cheers!

I wonder if it's usually the left-hand terminal that burns out because right-hand electricians are installing them.

Most likely reason is that the first contact is furtherest away from the actuator, and the flex in the plastic is enough to mean the contact pressure is low. Combine it with the stiff cable and the contact pressure is low, so the resistance as the contact ages rises, due to not enough pressure to wipe off the oxide layer, so the small area overheats, and then results in more oxide forming, and this then heats up more as the actual contact in electric contact reduces. With the electronics, I have some old breakers from the 1970's, which use a BRY39 thyristor to trip the coil, using the current generated by the sense coil to charge up a capacitor, and then use the thyristor with a 6V8 zener diode as a fast pulse generator to fire the trigger coil, though there is also a parallel path with some 12V zener diodes for fast triggering on high current, so that the time to charge the capacitor up is not going to cause a delay on short circuits. Leakage current it will trip within 2 full cycles, but large leakage ( like a short to earth) it trips on the same cycle. Nice application of a 4 terminal thyristor, pity they are not really made any more, like unijunction transistors, but at least you can emulate then somewhat using only a NPN and PNP transistor tied together.

(Sorry if I’m spamming this, I posted a few places) I started watching your videos a month ago, I stumbled upon your “A Simple Guide To Electronic Components” video when I learned about resistors after blowing all the LEDs in a 6v firework igniter box I was building. Point of the story: I’m 31 and have worked in kitchens (and one porn dvd rental shop) my whole life, I’ve never had any career I wanted or any hobby that could be monetized, until now. I have always liked electronics but now I am in love! I watch your videos constantly, most of it is a foreign language but I’m slowly picking up on it. If all goes well I will be going to school in the next year for an electronics technician. I have already converted my workbench over for electronics and have ordered a half dozen kits off of Ebay. Thank You Sincerely!

This reminds me of when I used to work in tv repair - Back in the 80s we used to see a lot of those old Ferguson TVs that used the Thorn TX9 chassis. These had an unusual thyristor-based PSU, and the most common issue with those was a burned up connection inside the mains plug, and it was ALWAYS on the neutral pin. Usually just cleaning up the connection (or in bad cases just replacing the whole plug) would result in a long-term fix but it was a bit weird at the time why it would always be the neutral end that burned up rather than the live.

So I've had a Nissan leaf for just over 3 years now. The high power CHADEMO chargers (400V, 120A, ish) have their own cable fixed to the unit and it does an insulation test before starting. The smaller, 3, 7 &22kw chargers you usually use your own cable and no test is done. I believe the contacter in the charger is fired when it gets a 9v signal from the car for EVSE chargers. Ironically the charger is actually in the car so the things on the street, despite being called chargers, are just fancy sockets

It would be interesting to compare the Rolec design with other 3-phase RCD's, like Schneider or Eaton

Obviously too much current on the contact. Raisins are 20% more conductive.

So much mechanical components and magnetic hacks which are life saving - scary.

Great video Clive

Love the brick!

That should not really do very much switching so I'm left with guessing between some sort of vibration mode parting the contacts slightly or just a poor contact with not enough pressure on the it to cause overheating during high current draw.

Hi Clive. Put a straight edge along the black plastic contact carrier and check for signs of twist. The burnt one is the farthest from the tension spring so has slightly less contact pressure. When the power ramps up the contact gets warmer and begins a self perpetual cycle of further reducing the contact pressure until it finally fails. My two cents.

Had a home Rolec charger. They are notorious for this fault. Replaced the RCBO myself. Apparently the newer ones are better.

RCDs are known to open or attempt to open under extreme overcurrent or short circuit conditions. So if the complete charging system (pillar plus cable plus car) causes a large current spike when plugging the car in, out or operating the motor while plugged in, this can cause more tripping than normal. Also, some RCDs are only rated for two such events in the lifetime of the RCD (there's a sticker telling homeowners to call an electrician if it trips from short circuit and to never reactivate it a second time). So if the regular operation cycles that scenario as often as once per month, contacts designed for normal RCD use may simply wear out.

Wonderfully informative - thank you! And what a fantastically authoritative, yet lilting voice. Warmest regards and thanks for the insight. Eddie

A stab in the dark, AC->DC we are well aware of but the AC->DC->DC thingy with highest current/best efficiency possible maybe a new ground?

Clive, the failure is most likely due to poorly attached wire in the terminal (externally), or a piece of insulation that wasn't properly removed... I see a lot of that out in the field, and it manages to cook the contacts the same way. Done a lighting relay last week that welded itself shut, because they didn't bolt down one of the terminals, and the wire just welded itself in place and eventually cooked the contacts.

They probably needed racing electricity. 87 electricity has too much resistance for the electric race cars.

Nice mechanical setup

Perhaps the edge-most wire gets pulled on and has insufficient strain relief, increasing the terminal resistance and producing heat?

Maybe worth feeding the circuit from a signal generator and seeing what does/doesn't make its way through to the output?

I believe the green sleeve, being constrained by the housing, reduced the contact force, making it get hotter until it finally arcs. I've seen similar problems before, always by something external reducing the intended contact force.

If this is an RCD without the ability to trip on overload, I wonder what current the actual overload circuit breaker was rated at? Just wondering whether it got into a situation where the current was too great for the RCD but not quite enough to trip the actual breaker, so it sat there slightly above its rated load getting quite warm over some time.

On the SpeakEV forums there's a large thread on failed Rolec RCBOs. Almost always the neutral and the seems to be a wonky angle where the contacts don't make good contact. Rolec blamed installers not tightening the screw terminals correctly but they have since issued a new green coloured switch version. Clearly made from better chinesium.

The neutral is probably loaded to the max and over, if you have stady current in every of the 3 phases the neutral current is the square root of 3 times the phase current. Then the neutral current can be higher than phase current.

Should have a notched hole to let the wires flex a bit more as well as centring the main switch to evenly try and displace pressure evenly along all contacts.

Here in the US there have been problems with overheated neutral in 3-phase systems due to poor power factor caused by electronic power supplies.High frequency harmonic currents do not balance out causing the neutral to carry higher then rated current.

Are type-AC RCDs allowed to be installed in the UK? I'm asking, because here in Germany those devices are prohibited; Type-A RCDs are the bare minimum here... Greetings^^

A guess would be when you reset this style of RCD the contact that is burnt is the last one to close (by a few ms?) because the lever is operated from the other side of the unit, the bar inside flexes, but in this application I can’t see that item being operated very often nor under load, so maybe other factors but that’s my guess. I have seen 4 pole breakers that have been pushed up from one side destroy equipment as the neutral connected momentarily after the phases. We confirmed this by testing it afterwards - was on one of our genset hired to a customer.

Actuating shaft for the contacts twisting as it gets further from the toggle?

Let me just pause while I take it to bits... Cut to explosion of metal parts... Mmm should have done that slower.. 🤣😁😂

Mayhaps that contact isn't held down as strongly because it's at the end of that plastic bar?

I'm guessing here, but if one contact breaks first or closes last (compared to the others) it will arc badly. If there's something loose (or just plain cheap) in the pivot shaft, it can do both - break first and close last - double the failure fun. This is a huge issue with high voltage, large capacity breakers - so much so that industrial versions have special snap mechanisms that slam them open and closed fast and along with arc suppression coils that quench any arc quickly. Even so, every time I've serviced one there's always one contact that's a bit more pitted and burned than the others.

the cut to the whole thing being apart with parts strewn all around the bench like everything just exploded made me audibly laugh out loud

Hey Clive , back in the late 80’s early 90’s prior to the introduction of RCD’s in Australia, we were using voltage operated ELCB’s which used two earth electrodes at a predetermined distance apart. Are you familiar with this type of protection. The concept of operation was that an earth fault would cause a potential difference between the two electrodes of approximately 22volts which would cause the ELCB to trip. I was only a first year apprentice at that time and didn’t really understand. If you are aware of these products please enlighten us. They weren’t around too long probably because of the complexity’s of there installation and the simplicity, reliability and effectiveness of the RCD. Cheers jj

I think the end contact burning is due to Newton, it will take just a fraction of a second longer to breake contact due to inertial forces causing twisting of the contact bar. All the actating forces are at the other end of the bar so it will twist a fraction as the contacts are opened so the far end will be the last to open so the system will try to draw all the power of that one line.

How about connection screw slackened off with heat cycling or wasn't properly tightened in the first place?

Could the neutral-wire, due to bad installation by the electrician, have been fed through "1" terminal on the RCD ? - combined with third-harmonic * currents from the charging-device raising the total current above 63A nominel current through "1" terminal? * third harmonic currents gather in the neutral + third hamonics happens because of rectifying from AC to DC (just like in a frequency converter) I know its a longshot :P

Is all the return current from the three phases going back through the burnt contact and overloading it?

A possible reason why it's always the left hand contact: The switch is on the right hand side, therefore when re-setting the breaker, the mechanism is tilted slightly due to the switch being off-center, causing the left hand contact to arc slightly.

I wonder if because the damaged terminal is furthest from the trip mechanism, it opens slightly slower and causes more arcing and burning?

So I have a theory on why it's always the far left terminal. It is the furthest from the switch, so the flex in the mechanism would cause it to be the last to move away, and it may not move as far. Allow more arcing then the others.

Bigclive, a fully articulated passenger bus caught fire here while connected to it's overhead charging port, and was unable to disconnect from it while on fire (might have fused itself to the connector). Fire department was unsure whether power was still on and decided to wait for the power to be killed, all the while the back of the bus was burning and they watched (American kind of situation, actually). I only got a couple of pictures of the bus on fire from a colleague, so I don't know how violent or interesting it really was, though it was a troublesome thing to see because the bus was merely a year old...

Perhaps there is a slight delay when the circuit is broken and the one on the left is the last one to break. That may spike the current on that leg as the load is still trying to draw current.

Another name for the arc quenching part is an "arc chute". Just an fYI. Thanks!

The breakers likely pull power, one after another from left to right mainly, which is why you'd see the left burnt/blown first on most units Don't know if that's the case, but it's a thing to think about.

at least here in germany a RCD type B oder type A-EV, which are sensitive for (continous) dc leakage current are mandatory for EV charging stations. These are really expensive. They cost 10 times much as a type A costs.

Hi Clive, Any chance of a video about variable frequency motors ? Wife liked film about mosquito !!!! Regards John

I wonder if the reason the left one fails most often is that the geometry of the pivot is a little sloppy on that end, slowing the break and allowing more arcing. Or, perhaps the slop makes that end a lighter connection with more resistance.

Was thinking , the switch is on the right and maybe the contact assembly is flexing and causing the left contact to open last or slower..

Is it always the contact that's furthest from the switch actuator? Maybe the springiness of the plastic causes it not to close and open as positively as the contacts nearer the actuator.

I would guess the spring that holds tension on the 4 contacts is either not strong enough when the RCD gets hot or the arm that hold the 4 contacts slightly twists causing less pressure to be applied to the final contact

Meanwhile in Sweden most of our charging poles are galvanized steel lol. Try chipping that with a weed whacker xD

You say the left hand one always burns, on 13 amp plugs the live terminal screws always seem to loosen themselves,strange.

torsion on the contractor bar, it latches from the right side, meaning the left side has the least force keeping it in place, and most torsion on it.

Wonder how branded one look inside. I have type A ones installed at home, they are Hager brand and cost a lot more than this Rolec

to me I think it is the spring is one end and the fault is the other , is it possible that it gets twisted over time and therefore that contact would be loosest and likely to arc?

Looking at it and seeing that the springamathing is on the other sideo of where the burnt contact is, it could be the contact with the least pressure. since its the rcd and no switch/fuse it shouldnt have wear from on/off arcing. (of course it gets tested each month...) aaand perhaps over phase L1 there is running more power than over 2 and 3. or even only on L1 depending on car charged.

Maybe it's whatever goes into one of the contacts? Like one lead or bar being aluminium for some reason (price) and running into contact issues?

Probably burns that contact because of play in the mechanism, with the activation system being at the far end any play could result in a difference in the contact action, it is probably the last to make/break.

Might be because the set of contacts are driven from the opposite end. Any slop or deflection on that shaft could result in less pressure on the far side contacts.

Interesting that you mentioned a car drove off plugged in as I thought the vehicles have a protocol to not run until they are unplugged???? Type 2 plug and socket with 3phase neutral Earth and two mini pins for the coms.

When thinking about the failure of the single contact: these contacts shouldn't be making and breaking very often at all. They should only open on a fault - right? And when they close they shouldn't be under load. There's another contactor that does the normal on/off function. I'm going down the path of a bad connection overheating. Was there a "fault" in the pillar or cable/vehicle that caused this device to trip, or was the only problem the failed breaker? Maybe (like you said) the cramped space for the wire was preventing the contact from seating firmly - causing it to over heat.

Is it not the neutral that is burnt? It handles return from the 3 other phases when using it for 230v and therefore more current?

I don’t like the way it armature picks up the contacts from only one side and not the center for balance. The contact on the end may not be getting enough wipe due to lack of rigidity in that arm type arrangement. Insufficient wipe (contact pressure) can definitely cause this problem too. I like your observation on the shunt being impeded and not being able to move freely. That seems to be the most probable cause.

The fault could be the fact that the left most terminal is the furthest from the "breaking torque" on the other side. Meaning when tripped or going into the off state the twisting force isn't enough to fully or properly disengage the left most pole. Perhaps why it's common to see the left side with problems. BTW, I think it's pronounced Wah-Way.

It seems like the delicate electromechanical approach might be sensitive to moisture and dust? I wonder if it would get annoyed at magnetic fields?

This circuit seems really weird to me. First they limit the voltage to around +-0.6V, which means the maximum voltage drop in the Current Transformer would be +-30mV in any winding. Fine so far. But now the RCD is supposed to trip at 30mA fault current, which will be 1.5mA on the secondary, which is then essentially passed through a capacitive voltage divider with the trigger coil in parallel to one capacitor. I don´t get what this is supposed to accomplish. If i´m not mistaken, the arrangement of capacitors (effectively 15uF in series) at a trip current of 1.5mA through those, would result in a rate of voltage change of 100V/s across the diodes. Without the capacitors the voltage could rise as fast as it wants, until it gets clamped by the diodes. But since the trip coil surely has a significant inductance, I´m not sure why that would matter. Maybe they want the trip coil to form an LC resonant circuit with that capacitor to help it demagnetize?

I'm actually not suprised about the circuitry. I have recently disassembled an old RCD that was installed around 1985. It was kinda the same mechanism. The trip coil was connected direcly to the detection windings without any circuitry at all.

theirs a communication pin on EV charging cables that check connection before starting any charging. Nice video Clive nicely links in to my YT channel about electric cars can i use some of your footage for a video on mine for B-Roll?

I almost wonder if the station is wired correctly inside. could one of the phases be under a higher load where the RCD is connected to the source directly instead of through a master breaker, and the charging circuit and control circuit combined are close to exceeding the rating of the RCD, if not exceeding it?

Your "Tramp Brick" is hilarious and clever.

Well Clive if you're puzzled then I've got no chance. But did you check for gremlins?

@8:45 those are tantalum capacitors.

That burnt terminal looks to be living in an area more tightly closed off from the others with slightly less ventilation. Maybe the cause of common failures on the same terminal?

The control circuitry may be running off the left hand terminal, the control circuitry might draw a lot. Have not seen any of these charging stations, do they have a street light or anything attached?

Hmm, you all use wye connection for 3 phase? Delta is more common in the US. At any rate, that black piece with the metallic tongues appears to spring against the rising cage contacts. I wonder if the plastic is flexing and is not developing enough force on the end to keep a solid connection. Also, gardeners "strimming" weeds? Do we need a Clive-speak wiki?

Did it break and not work afterwards or did it failed without tripping? Maybe it was just an too high current from a short on that channel while tripping?

! Mega Watt chargers arriving eh? I wonder if these are going to be with their Super Capacitors? I would love to see those.....from a distance.....

I suspect the neutral was connected to that terminal and I suspect the neutral current is very high, I've seen things like that before and it always affects the neutral. In New Zealand the RCD's that must be used to vehicle charging are type B RCD's

maybe improperly being used as a service disconnect switch? alternately, lightning surge jumped the gap as it tripped or maybe it was off and it jumped it, that could explain the fiber board chunk blown broken. hmmm

We had the same problem with a new apartment in China. Twice they replaced a Siemens RCD before ripping out all the wiring and replacing it with better quality not a small job. Might be a bad batch of cable?

My thoughts about that circuit are that I haven't a clue how it works. In order for the trip coil to cancel the magnetic field of the permanent magnet it must pass a specific polarity dc current but there's no circuit element that could create such a current. A charger circuit would normally take an ac load current and the sense transformer cannot pass dc even if there was some present in the load current. The only type of load that takes a dc current is one with a half wave rectifier at the input which would only be used for the crudest low power circuits.

2:51 Clive did you notice your electrical tester screwdriver lit up as you was removing the rubber plug in the back. Why would it light up?

what is inside and how it working sony crt tv