RCD Testing Rig Overview - Pulsed DC on Type AC RCD Fails to Trip
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- čas přidán 24. 07. 2019
- Overview of a testing arrangement and some quick tests to demonstrate the effect of pulsed DC on a type AC RCD.
The black box is used to create a fault to earth, equivalent to the insulation in the heater being defective. Fault current shown on the multimeter in mA.
This test places a single diode in series with the heater, effectively running it on half power on pulses of DC at 50Hz. This arrangement was commonly used in heaters to provide a full/half power option with a single switch.
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This is an eye opener for relative amateurs like me! Much kudos JW, we need to be aware of this stuff.
I am an engineer and I think your videos are brilliant. I love the little bit of dry humour now and then. That really tickles me. Nothing but good common sense and practical electrical engineering talk with some theory thrown in. I just wish I could spend an afternoon with you on one of your jobs. I think it would be an absolute hoot. Brilliant john and just ignore the odd bad comments. The engineer that never made a mistake never did much. Just brilliant John keep them coming. Allister B.Eng etc. etc.
I agree with comment below. The schematic would have added extra clarity. Thanks for another great video. You are the best on youtube for explaining technical topics in a comprehensive understandable manner.
Thanks, John - a great video as usual, and an interesting series of tests in prospect. How about drawing the relevant internal schematic on the tops of your test boxes - that would clarify the verbal description. Cheers!
reqordist A picture is worth a thousand words...
Great explanation 👍👍👍👍👍
A very interesting experiment. It would be great to take a look at the waveforms.
Here you are, Schaltung is circuit, Laststrom (load current) and Fehlerstrom is fault current. And you can see which RCD type is covering which type of fault:
upload.wikimedia.org/wikipedia/commons/3/34/RCD_Fehlerstromarten.svg
Here in Germany the type A is the common one, AC was banned for new installation in 1984. The old ones were phased-out: When the AC RCDs were defective (mostly tripped below 50% of the rated current), they were replaced with type A.
Given the nature of modern loads, why are manufacturers supplying ac type rcds and why are electricians still fittings them? Seems like a massive elephant in the room to me.....
Manufacturers are still supplying them because there's a demand for them. The electricians are still fitting them because they are permitted to do so by the wiring regulations.
Here in Germany the VDE prohibited the installation of type AC RCDs in new electrical installations in the regulations they release. And to make things worse: They already did this in 1984! So most RCDs here in Germany are type A RCDs. In my opinion that's much more a problem which should be solved than arc fault detection.
I would not make it mandatory to replace them, but I would make it mandatory that in case of a replacement of a defective RCD they shall be replaced by type A. A single phase type A RCD costs round about 20 to 25€, without installation. RCBOs cost a bit more.
Some of us are buying Hager who are supplying Type A with their boards and in RCBO's.
@@johndufton9686 The costs of them are reduced if they mass produce such things and can sell them in several countries. A type AC RCD/RCBO would be a special thing, even if it offers less protection and contains less effort, it is actually cheaper to mass produce the type A because they can sell it almost everywhere in Europe. The type AC is limited to some countries. Hager is a german company, and in Germany the type AC RCDs are not permitted for new installations (actually this is the case since 1984).
Have you ever seen how these things are made? There's only a guy filling the several funnels with the correct parts. The assembly is completely performed by a machine.
@@Marcel_Germann They are late on everything here in Uk still using two separate taps hot/cold, the very last ones that stoped asbestos in homes and the list goes on in building business.
@@Naughty_Squad Foundation earth electrode, or soil embedded electrode in all buildings, no matter which type of earthing system the DNO provides. Coming soon in the next amendement of BS 7671, in Germany mandatory for new construction since 1980.
Hi John, when you tested the RCD with the Megger Tester, you tested on the 0 to 180 phase of the AC waveform, what did the 180 to 0 phase of the waveform test too?
Pure genius 🇮🇪
I take back the wago idea this if far more organized and comprehensive . This diode test is also appliable to older AC RCCB?
0:24 did I see the heater supply lead wrapped AROUND the heater! Or will all be revealed?
Hi john do you recommend when changing c.u 100 amp type A rcds now. I still see alot of AC ones going In. Also there is a big price difference alot of people will be cheaper because installing the A.c ones thanks
Instructions unclear.
Found out why I was tripping out. . . That'll be those funny mushrooms again. . .
Tea anyone??
John, Were you doing phase to earth faults in this test? I.E. here in US ground fault. Here in US our GFCI devices are set to 5 miliamps, and 30 ma for specialized equipment. I'm not understanding how changing to D.C. After the device causes the unit to it trip. How do yours work?
good Video I like
Have you tried a combination of both AC and DC leakage currents, which is a more likely scenario to see when or if it trips
Jw i love your videos, where was you 15 years ago ✌️
In his shed. As always.
hi love your video on this subject quiet informative....i have curious question....whould it be possible to measure the DC current coming from the diode using yr multimeter....or if anyone knows tha answer please let me know....THANKS
Hi! @John Ward great, easy understandable video! Thanks
Could you give us advice what RCD type should we use in house equipped with Induction Cooktop? In my region AC type is massively used without any deeper thinking.
Type A as a minimum, and possibly type F.
Type AC are only suitable for purely resistive loads, which is practically nothing in a modern installation.
@@jwflame "practically nothing in a modern installation" but in reality massively used with a sense of it correctness even in freshly constructed building - at least in my region SE Poland.
Hi, Thanks for the video, so that socket on the left is wired in series? with the other sockets so the diode being added is being added in series to the load meaning that a heater or whatnot with a diode in it wont trip the RCD. The question I have is will it stop the RCD from tripping when the device with the diode is wired in parallel to the device with the fault?
The diode will fail or the MCB will trip.
JW, interesting video. I guess the question which springs to my mind, given the high likelihood of actually having one or more AC-type RCDs, is: Can we built a work-around device that will allow the AC-type RCD to trip at the appropriate current when faced with pulsed DC (or even normal DC too, I guess)? Something that can be used *like* an isolating transformer in that the item of equipment in question is plugged into this device, which is itself plugged into the mains power (note that I'm *not* saying that it should be in any way similar to an isolating transformer as such, but simply that - like an isolating transformer - it goes between the item of equipment and the wall socket). Any thoughts?
if there was a transformer of any sort then the RCD would not even be able to see the fault (not even a type A RCD would be able to detect the fault)
I work for the council and I informed them that the Crabtree boards we were fitting only had type ac rcds fitted in the split load and we should be fitting type a rcds so electrical safety is put in place but Crabtree still have not changed the rcds to type a
PS Can you describe your rig in detail please, especially the injection of DC and the knobs? I want to buid one !! Thx K
Now that type A type rcd's are made more or less mandatory in amendments 2 what would you code the use of a/c types on an eicr considering the amount of electronic equipment used today ?
C2, unless it's supplying fixed resistive loads only.
So why wasn't these AC type RCD's removed years ago from production?
Too bad that the test button isn't working on that RCD. It would be interesting to demonstrate that the test button won't work too if the magnetic core of the measuring coil of the RCD is saturated with DC. And when the fault is gone the system will work as intended again. Makes the search for faults interesting...
There will be several other videos on this, covering all of those things.
if DC fault current is high enough the test button does not work, the test button creates an AC leak, usually above 30mA!
@@ianlouden7939 I know, and that would be interesting to see and show that it won't work when the core is saturated with DC. But the test function of the RCD used here was defective, so you can't show it....
Why didn’t you test the trigger time? It is very important to know. Especially if you have NOS or used RCDs.
Hi John…another curious question after a year of trying to find the answer all over the internet…can a DC clamp meter read the DC current in a AC circuit…a ramp test would do the trick…but that would mean leaving all the appliances etc powered on….looking forward to your reply….THANkS
happy 2021 to all...my question is...with that diode plugged in or there was a capacitor leaking DC to earth...would that circuit pass an IR test...could someone let me know
A good capacitor won't affect IR tests, as capacitors block DC. A faulty one could, if it was leaking DC.
A diode would depend on which polarity the test voltage was applied, it would block in one direction but conduct in the other.
Just what you need during the summer - two electric heaters on! 😥
Climate change is all JW's fault.
You had the mains cable wrapped around the heater. Was that wise?
Probably not. However it was only on for a very short time so the outside didn't get hot.
Even I don't understand why your fault current changed with the load, and I did watch your explanation video. It _is_ a bit confusing after all, with all the black boxes ;-)
BTW don't you have any limits on harmonics in the UK that prevent you from using a diode on such heavy loads? It can cause problems with overheating transformers, because of saturation.
It's your channel and you can do whatever you want obviously, but if I am to understand it fully you'd probably have to show me a schematic of your test setup.
The fault current changed with load because the black box is just a current shunt with wire-wound pots in series from the hot end through the current meter to ground. So the ratio between shunt resistance and combined pot resistance determines the ratio of the main to leakage current. But yes I agree, we need to see inside the black box to be certain.
I had no idea that a single diode could defeat a GFCI (or at least some types of them). I'm going to test ours.
Finally got the nerve to test them. I was worried after looking online and discovering that rating GFCI's for pulsed DC doesn't seem to be a thing over here (there's "just GFCIs")--so some part of me didn't want to know if mine worked on DC. Fortunately, they worked (even the one that's 30 years old)!
It seems like high fault currents; does this mean the RCD's have limited protection abilities?
It depends on the type of fault current. The type AC only protect against AC faults. And in times of more and more switch-mode power supplies in residentials (mostly chargers for smartphones, tablets and so on) you actually should think about changing the existing AC-RCDs to type A RCDs. Type A will protect against pulsating DC and in addition AC faults. Type B, which will also protect against DC faults in addition to pulsating DC and AC, isn't necessary in most cases. I would only use them in a circuit for chargers of electric vehicles in a residential environment. So AC is practically the basic protection, the other types put protection against other fault current types on top.
Actually here in Germany it is prohibited to install type AC RCDs in new electrical installations since 1984. So almost every RCD here is a type A which would protect you even in that scenario shown here.
These DC or pulsating DC faults are practically "blinding" the AC RCDs, so they won't trip. The DC current is saturating the magnatic core of the measuring coil inside of the RCD. It won't trip, even if you press the test-button. And that's the thing John couldn't demonstrate here because of the broken test-button on this one, but even if it works, in the case of DC it wouldn't work at all.
It is unusual for a domestic device to have a DC leak to gnd, devices like hairdryers etc that use 1/2 wave rectification where the load is DC has no bearing on the RCD, a Type AC will still trip if there is an AC fault somewhere. So long as the DC current is opposite and equal on both poles of the RCD it is unaffected. The issue arises when you have a DC earth leak present (that bypasses one of the RCD poles) below the typical trip level of the RCD (in this case
if equipment has a full wave bridge rectifier, the ac supply and rcd should i think 'see' an ac load so should trip normally..????? have you tried this? maybe rig up mains in, feeding bridge rectifier with capacitor and resistive load, and simulate leak to earth from each pole of the capacitor in turn, that's what you'd get with something like a bad 'leaky' usb charger , most have bridge input, although not all ..?? none of the usb chargers i've come across have 'earthed' output, all float, so could easily be shock hazard under isolation failure , all my laptop chargers that have a 3 core mains lead also seem to have floating output, the earth is unconnected..maybe to stop possible ground loops with other equipment? maybe they could fit some sort of 'avalanche' device from output 'ground' to earth so in normal conditions output is floating, but if the output develops an excessive voltage to true earth, the device shorts and blows a supply fuse in the charger and/or the plug fuse?
What is the difference beetwen AC RCD and A type RCD ?
AC reacts to AC current only, A does AC and also pulsed DC.
There are many other types.
@@jwflame Thanks for info.There are B type RCDs which react under AC,DC and pulsed DC.
With double insulated equipment how many people get electrocuted today with faulty goods?
There are also class I appliances with such problems, for example a desktop PC. They're always class I. Next one is the charger of an electric vehicle, in that case the car is the appliance and class I too, the charging electronics are in the vehicle. And one defective class II appliance with a DC fault can influence the RCD, it won't work anymore, even on AC faults as long as you got the DC fault. Meaning this is bypassing and interrupting the whole protection of the RCD. Second fault and you got a problem, even if that fault is AC for which the AC RCDs are made for.
If you think this way we could turn back to the old days, spare the money and don't install RCDs anymore...these things are there to safe lifes. That's the reason they were introduced at first for circuits in rooms which we're most vulnerable in: The shower and the bathtub.
@@Marcel_Germann How many people get electrocuted from faulty equipment? You explained the purpose of RCD's however there are still a lot of houses without them. True better to have them then not. They had a big push of RCD's with electric lawn mowers people going over the cord with the mower.
@ How high is the value of a safety feature that won't function under some circumstances? Circumstances of living are changing from decade to decade. What and how many entertainment appliances did we had 35 years ago? A Stereo system, a TV and mostly that was it. Now we have PCs, LEDs instead of incandescent, flatscreen TVs instead of vacuum tube TV, surround audio systems, a handful of chargers for battery operated appliances like smartphones and tablets and so on.
In most cases people won't die, but they'll get an electric shock and the RCD is not tripping. In most cases the current is limited by the resistance of the clothing they wear (shoes, socks) and the resistance of the floor. An adult person won't die if the person is healthy. But persons with a heart disease, childrens and animals could be not as lucky.
The reason for introducing RCDs at first here in Germany was for TT grids. The earth impedance is very bad compared to the impedance of the grid. So you needed something that shortens the tripping time in case of a L to PE short-circuit, L to N was no problem. Later they came up with the idea to use it as a safety feature when they were able to manufacture 30 mA RCDs (the first ones had tripping currents of 500 or 300 mA. And here in Germany they were introduced for circuits in "rooms that contain a bathtub and/or a shower" in 1984. Also for outdoor circuits.
The thing of this video is to prepare you for call outs when a customer calls you that he got shocked and the RCD wasn't tripping. You come over, test the RCD without load and it will function properly. Then, and after watching this video, you got back in mind: Hey there was something going on with type AC RCDs and some appliances. If you're dealing with a system you'll have to know its flaws, otherwise you'll get problems finding a fault in it. In that case you'll have to find the faulty appliance before it causes other damage like catching fire or something like that.
And for new installations it's using the right type of RCD for the circuit. For example if you're installing a wall charger for an electric vehicle the right type would be a type B RCD. Or type A+EV (cheaper than B), or if the charger got a DC protection integrated a type A RCD would be sufficient. The type A+EV is not a standard type of RCD. These are the standard ones, here in Germany we use mostly type A. Here you can see from which type of faults which type of RCD will protect you. Schaltung is circuit, Laststrom is load current, Fehlerstrom is fault current. You can see, the more the waveform of the current is deformed, the more unlikely the AC RCD will trip. The A type RCD includes AC and extends its functionality. The same is for type B which includes AC and A and extends it for DC. B is the most expensive, for most applications a type A is sufficient.
upload.wikimedia.org/wikipedia/commons/3/34/RCD_Fehlerstromarten.svg
I would not go that far to make it mandatory to replace them now. I would phase-out the AC RCDs step by step. If you got a defective one or one that is noticeable and reached the end of its lifetime, I would replace it. And in new installations I would no longer install type AC. That was the way we did it here to keep the costs for the customers low.
Marcel Germann - just three comments. Yes these days, there are a lot more appliances and gadgets that convert the AC mains to DC. However, old mains radios (valve/tube) and most non-portable TVs (CRT type) have always rectified the mains voltage.
This looks like the people who write electrical standards have ignored the devices, appliances and gadgets that electronic engineers have been creating since the 1940s...
Oh, some devices, appliances and gadgets where a mains transformer is used are very unlikely to cause DC fault currents to flow in the mains side wiring. But this may not be true for devices, appliances and gadgets where switch mode power supplies are used.
@@Mark1024MAK There's a difference. The old ones transformed the voltage down, than rectified it. That means the galvanic isolation from the mains, which was performed by the transformer, was before the rectifier. That caused no problems, especially since the voltages are low. On new appliances the rectifier is before the galvanic isolation, the DC voltages are potentially deadly, referenced to earth and 1.4 times the AC mains voltage. I know the anode voltage of old tube radios was high too but the circuit could not deliever much current, and wasn't referenced to earth in most cases. And back in the days there were also cheap, crappy constructions like the universal current appliances. They had no galvanic isolation, reduced the voltage with a voltage divider. They were functional with both, AC and DC as a mains supply. And depending on which way arround you put the Schuko plug into the outlet (Schuko is not polarised), the metal chassis was live at mains voltage or not.
John, A video idea for you. In your country, you call the three prongs on your plugs hot, neutral, and earth. Laymen in US call it ground. Professionals call it equipment ground. About 99% of people over here are confused and probably most over there as to what these third conductors really do. Most think the short circuit goes through that conductor to earth grounding point. Set up for video would be a standard RCD(circuit breaker) in a Consumer Unit(panel). Run one single conductor from there to back yard. Install a switch, then to a rod driven into the earth. Turn on the breaker, then the switch. Take an amp draw, and show worms coming up out of the ground. The RCD(circuit breaker) will not trip. Hence proving that short circuit absolutely does not go to earth to cause a trip! Note I said Standard RCD not (ground fault or arc fault).
Your message is rather confusing, to say the least. The normal terms used by electricians are Line, Neutral, and Earth, others use Live instead of Line, nobody uses Hot is not one of the terms in common use in the U.K.
Also since the house earth is connected in the service head (in the majority of wiring systems in the U.K. )to the electrical supply company earth which is at or extremely close to ground potential, your test is extremely unlikely to function
JM SometimeWoodWorker The terms used are different as you say. I agree! But, if you connect a conductor to a (circuit breaker US) to a rod in the ground, I assure the "over current protective device will not trip. Not enough amps. I am sometimes woodworker as well. Respectfully, Kevin
We say "line" not "hot." We used to say "live" instead of "line" but that changed (neutral is also considered live because in certain fault conditions it can be lethal to touch it). We also use "RCD" to mean "residual current device," which we used to call an ELCB (earth leakage circuit breaker).
So in your test, a residual current device would trip at 30 mA. An ordinary circuit breaker might or might not trip, depending how good an earth connection your pole makes.
bdf2718 Wow, I have a lot to learn on how to talk the same electrical language over there. 😊. I'm not positive what amp ratings you guys use over there. I'm guessing 10a and 16 amp overcurrent protective devices. Not a 30 ma device that compares live to neutral. If you make direct connection to a rod driven in earth, the so or 16 amp standard device will not trip. Not enough current to trip it. It might if you left it on for hours. This would show that your so named earth conductors at receptacles do not carry the current to earth to make the device trip.
@@KevinCoop1 Ummm, maybe you should stick to woodworking. :)
We have 230 V (nominal, because European Union, actually closer to 240 V), not your 110 V. Breakers are usually 6 A for lighting circuits and 32 A for sockets (higher still for cookers, immersion heaters and power showers). 32 A sounds like a lot, but that because we often have a weirdness called a "ring final circuit" which means that all power plugs *must* be fused, to a maximum of 13 A. See en.wikipedia.org/wiki/Ring_circuit
Both here and in the US, if you short the line (hot) to the earth pin of a socket then the overcurrent device *should* trip. In most installations here, the earth conductor is connected to the neutral conductor at some point between the distribution transformer and the consumer unit. And that neutral is very well earthed at the distribution transformer. In rare cases, consumers in isolated buildings have to have a local grounding installed and there are rigorous checks to ensure that it *will* carry enough current to trip breakers. JW did some videos on this. See also en.wikipedia.org/wiki/Earthing_system
If you stick a random bit of pipe into the ground, you probably won't get a low enough impedance for a short to it to trip the breaker. But you might, especially if you live on swampy land. One of JWs videos discusses what you might have to do to ensure your ground is good enough.
Are there specific RCBOs for DC? Can a type B RCBO be used in solar pv circuits?
RCBOs are mostly type A or AC. But there are type B RCDs available, but be prepared: They are quite expensive compared to type A or AC RCDs!
@@Marcel_Germann Thanks for the very helpful reply. I came across an RCBO on the following website; en.chint.com/index.php/product/detail/id/1027.html. If you take a look at the accompanying PDF under "catalogue", it claims it's type B,C, and D. I was wondering if this implies this can be used in solar pv circuits. I know Chint is a Chinese company but they appear to be reputable enough.
B, C or D defines the MCB tripping curve, not the RCD type. MCB type B is usually used for domestic, C&D are usually for industrial machines.
@@adon8672 In that case B or C are the tripping curve of the MCB part. The RCD part is AC only, it has only the AC wave on it. Here are the different type of RCDs, there you can see the symbols which are printed on the RCD, the circuitry which could create a specific fault, how the load current is behaving and the fault current. You can see what faults the different type of RCDs are covering:
upload.wikimedia.org/wikipedia/commons/3/34/RCD_Fehlerstromarten.svg
So type B RCD is something different than it is on the MCB. Type B RCD (!!) is protection against AC, pulsating current and smooth DC faults.
That's a type A RCD, take a look at the picture, next to the red indicator is the symbol for type A RCD. It got the AC sine wave, and the half sine wave for the pulsating current:
www.amazon.de/Eaton-236748-FI-Schalter-40A-30Ma/dp/B000UW4EGE/ref=sr_1_16?__mk_de_DE=%C3%85M%C3%85%C5%BD%C3%95%C3%91&keywords=fi+typ+a&qid=1564440539&s=gateway&sr=8-16
BTW: I would never buy that thing from China. They only got the CE, which is no certification at all, it is only a self-declaration by the manufacturer that it fulfills minimum safety requirements of the EU. Here in Germany most service companies demand in their technical connection conditions that you must install VDE certified devices. Or at least certified by another recognized european testing organisation like the austrian ÖVE.
John leaves out lots of info to give room for the clever guys to comment...
Pls do megger video John.
A bridge rectifier passes current on both half-waves, not just one. It does not create the same pulsed DC as a single diode.
If you had an isolated, differential oscilloscope probe, you should be able to see clearly whether an appliance is drawing current on one or both half-waves.
bluerizlagirl It’s still unidirectional. It’s not the pulses that’s causing the RCD not to trip...
@@kennethcohan9630 With a bridge rectifier wrapped around the load, the current is flowing through the breaker on both half waves. With a single diode in series with the load, the current is only flowing through the breaker on one half wave.
bluerizlagirl My understanding is that it doesn’t trip because it is DC and not AC and so it wouldn’t matter whether it was full wave or not, it is still DC.
@@kennethcohan9630 No. The current flowing through the breaker is alternating, and flows on both half waves, when the load is inside a bridge rectifier. As far as the breaker is concerned, it is an AC load. What causes trip failure with half-wave loads is the fact that current is flowing only on one half-wave.
bluerizlagirl yes, you are correct. With a full wave rectifier, under fault conditions, AC would be flowing through the RCD and it would trip.
(6:00) - Surely, a diode isn't going to give you pulsed DC but rather just half of the sine wave.
I mean, isn't pulsed DC a square wave?
Please, I'm struggling here.
>
Pulsed DC can be a square wave, but can be other forms, the main thing is that the pulses are all of the same polarity.
@@jwflame Oh I see.
Thank you for replying.
>
I believe wylex RCBOs have always been Type A
Well none of this makes sense of course. BECAUSE: 1) Type A RCD tolerates 6mA before saturation , but it is STILL an AC leakage detection device !!. It simply means it will still operate under AC loses in an environment of up to 6mA DC offset. 2) So, what you needed to do here is apply various DC offset currents and use your MEGGER in the AC testing set up. It would then be VERY useful to see what amount of pulsed DC from the diode would be needed to be injectedt to block the AC RCD device tested for AC leakage, 3) The DC current that the type A will tolerate before saturation is 6mA. This is quite small. So in effect type A will behave the same as type AC when the 6mA is exceeded, by specs !! Your rig can test for this also! 4) Most of the demonstrations done to show the impact of DC offset on AC RCD operation is using either 50mA or 250 mA of DC, then testing for AC leakage. I bet you any money type A will not operate under those test conditions either (ie 50mA DC offset, tested for AC leakage) since by definition it is rated to tolerate only 6mA of DC. 5) How would a latest AC RCD behave in an environment of 6mA or 10mA of DC offset?? I have seen no one test this out !! If for example a good brand of AC RCD of today eg MK can tolerate 6mA of DC then it is no worse than a type A. So a lot of talk but no real data to support the new regs. Your rig can test this out, but you have not done that, please do, we need the info.
Whilst ramp testing RCDs, i would test with no loads attached.
In a ramp test without a load they would be functional without any problems. The problem is that DC and pulsating DC are saturating the magnetic core of the RCDs measuring coil. So it is actually "blinded" and can't work properly. Even the test button won't be functional any more as long as the DC fault is there. If the fault is gone, the RCD will function as expected. The thing is, these types of failures come from defective switch-mode power supplies, photovoltaic installations or chargers for electric vehicles. The last two are in most houses uncommon, but the first one is a major problem. Almost every appliance now has a switch-mode power supply in it. Even the small chargers for smartphones or tablets. And they can produce such faults where an AC type RCD isn't protecting any more. That's the reason here in Germany the type AC RCDs are not permitted for new installations since 1984, the common type of RCDs here is type A which protects against pulsating DC (unsmoothed DC directly from the rectifier) and AC faults. It can't be blinded with pulsating DC. On AC faults they're as fast as the AC ones, but on pulsating currents they have a little longer tripping time. But it is still within the limitation of 200ms.
@@Marcel_Germann im talking about going in to an installation that may have a fault on a final circuit protected by an RCD. To rule out a fault with the RCD, i would Ramp test the RCD without the final circuit on load. If the ramp test is sufficient, i would then IR test the final circuit to find fault. I was under the impression thats what the ramp test is for; whats a ramp test going to tell you if you have a faulty final circuit on load?
@@lesterelectronics223 The test will indicate that the RCD is functioning inside of its specifications because you're performing this test with AC. BUT the problem is we now use more and more appliances which produce fault currents which disrupt the functionality of the RCD. Even up to a limit where you can say it is deadly for a person. Phone or tablet chargers, EV chargers, PV and power supplies of PCs. Everything that contains a switch-mode power supply. All these appliances could cause such massive trouble if they fail. In such a case it is as you don't have an RCD installed, because it is practically disabled by DC.
The switch-mode power supplies are working the way that the first step is to rectify mains voltage and then convert it down to the wanted voltage. In that case you got a dangerous voltage which is no longer AC and is higher than mains voltage (rectified voltage = RMS mains voltage AC multiplied with 1.4), if there's a fault occuring the AC RCD won't trip within the specifications (15 to 30mA) and the person in contact will be propably toast. The type A RCD will trip within the specified 30mA limit (between 15 and 30mA). 30mA is the threshold were it could become critical for an adult person, this could cause cardiac arrest. For children and animals the treshold is actually even lower.
In conclusion: They're not dangerous, but you must know what you're dealing with and that in some cases the type AC RCD won't protect you depending on the load you got on the circuit. LED lights are also such nice guys which produce such faults. Back in the old days of the incandescent lamps there were no such problems. I would only change the AC RCD against a type A if it is defective. This will limit the costs for the people. No need to make a retrofit mandatory. But I would only use type A or B in new installations, and replacement of broken type AC with type A.
Take a look at this video, this is the whole theory esplained. The video was created by the e5 group:
czcams.com/video/9qX89cPGgp4/video.html
They also perform several tests.
@@Marcel_Germann i undetstand what your saying. It all comes down to the manufactures of the said SMPS/LED. Any SMPS used in the uk should be built, tested and inspected to a certain standard such as BS EN 60950/62368, and 62504 for LED lighting. With double improbability designed in the products to fail safe during a fault. Creapage distances and clearance/insulation between mains voltages and ELV parts mitigates against receiving an electric shock during a fault. All products would have undergone vigorous testing such as; high voltage withstand testing upto 5Kv (dependant on voltage category of the item and class) to test input output isolation. Pulse testing to name a few (replicate a lightening strike). If carful selection of LEDs and SMPS are taken into account, you should not have to rely on an RCD to protect you if the item fails within, but only on the mains side to the casing of the item (if class 1). On a side note, with the intoduction of SPDs (18th ed), these too could be mittigated; a well desiged SMPS to a british standard will contain MOVs/GDT to clamp the voltage during a lightening strike. Where does the electricians responsibility end? Do we now have to recommend what end products the customer can plug into their sockets too guarantee safety? Police the electrical crap that ends up in this country, would mitigate against most electrical injuries/fires and make the electricians job easier.
@@lesterelectronics223 Every appliance could fail, the only thing is to limit the damage they do in that case. It could not be by design, abuse of the appliance before is also a possibility (throw it out of the window and you can't expect that it will function proper and safe again). That was the reason RCDs were introduced in the first place, to limit the damage to persons and property. The problem is that the circumstances we live in now have changed over the last decades. Now we got other types of electronics than 30 years ago, and we got a lot more appliances than back then. Back in the days we got incandescent lamps, a stereo audio system, a TV with a vacuum tube screen and that was it with the home entertainment. In most cases they had proper power supplies with a big heavy transformer inside. Now these days everything must be compact, leading to switch-mode power supplies which are extremely compact and efficient. But now we got a lot of them in our homes. Notebook, tablet, smartphone, audio surround system, BluRay players, streaming devices and so on. And the incandescent lamps were replaced by LED lighting, which now require a DC power supply. They all could create this trouble, even the electronic of the motor of your washing machine could cause that trouble with the RCD.
The most important thing is: Electricians should know about this flaw, otherwise you'll never find the failure if a customer calls you and reports that he got an electric shock but the RCD didn't trip. And electricians should know that there are different types of RCDs available, and they should pick the correct type for the circuit. And in most cases this is no longer the type AC. AFAIK this is introduced in todays edition of the BS 7671.
If you install a circuit for a wall charger of an electric vehicle you got different options:
1. Type B RCD, protecting against AC, pulsating DC and smooth DC faults.
2. Type A+EV (not an official type)
3. Type A and the DC protection is included in the wall charger.
I would leave the AC type RCDs in place as long as they don't cause trouble. If they do, for example through aging they become more sensitive and trip even without a problem, replace them with a type A in a normal household circuit. When installing a new circuit use the correct type. There's no need to make it mandatory replacing the AC type RCDs. Just phase them out at the end of their lifetime and replace them by an apropiate one. That's the way this was handled here in Germany. The costs are the same, doesn't matter if you buy a type AC or type A.
Here you can see what type of RCD can be used for which type of fault. The type A includes the AC protection, and type B includes the type A, AC and offers additional DC protection. Schaltung is circuit, Laststrom is load current and Fehlerstrom is fault current:
upload.wikimedia.org/wikipedia/commons/3/34/RCD_Fehlerstromarten.svg
The price is not too high, this Eaton one (40A, tripping current is 30mA) costs here 26.35€. By todays exchange rate: 23.65 quids. Is suppose that's in the price range of an AC type RCD in the UK.
www.amazon.de/Eaton-236748-FI-Schalter-40A-30Ma/dp/B000UW4EGE/ref=sr_1_5?__mk_de_DE=%C3%85M%C3%85%C5%BD%C3%95%C3%91&keywords=rcd+eaton&qid=1564152309&s=gateway&sr=8-5
That's why AC type RCDs have been prohibited in Germany for ages.
Since 1984 to be exactly. That was also the time the VDE introduced the regulation that the electrical installation "in rooms which contain a bath tub and/or a shower shall have RCD protection".
@@mernok2001 West, the VDE was a west-german institution at that time.
On the merger, you were supposed to start with 30ma and test it for all angels. That is how it is done. The last setting which you testing it on is ok but still, you needed to test step by step for 180 degree and others. Half-wave etc...
Agreed - half wave is exactly what the diode in this test rig is simulating.
Just goes to prove that although they may be a better bet than an old fashioned MCB they are no substitute for a good RCBO ……..
an RCBO is just both MCB+RCD in one unit. They work the same way
You can also get type A RCDs as a separate device:
www.amazon.de/ABB-FI-Schutzschalter-25A-F202A-25-03/dp/B001L5SLP4/ref=sr_1_4?__mk_de_DE=%C3%85M%C3%85%C5%BD%C3%95%C3%91&keywords=rcd+30ma&qid=1564064896&s=gateway&sr=8-4
The type AC RCDs are banned here in Germany for new installations, actually that's the case since 1984.
@@jaycee1980 I understand that. There are specific MCBs and RCDs for DC. I just haven't come across RCBOs specified for DC and that's why I'm asking.
300+ is about 15 times more, not 10 times.
10 times more than the rated 30 mA trip current.
@@Berkeloid0 aha ok, i thought 21 mA.
That particular RCD is a 30mA one, but tripped at 21mA, which is within specification.
@@jwflame thanks, yes i understand.