The Complete Guide To RCDs - Residual Current Devices

Most circuits within a modern electrical installation are protected by an RCD or Residual Current Device. RCDs offer protection against electrical faults and electric shock. However, as electrical installations and connected appliances become more complicated, this places additional requirements on the designer to ensure the RCDs are matched and offer the correct levels of protection. In this free accredited CPD training module, we explore using RCDs as defined in BS7671 UK wiring regulations.
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00:00 Introduction to RCDs
01;20 What protection do RCDs provide?
03:40 How do RCDs work?
08:40 DC leakage currents & non-linear electrical loads
12:30 Different types of RCD
13:00 Type AC - RCD
14:10 Type A - RCD
15:30 Type F - RCD
17:10 Type B - RCD
18:40 Installing the correct type of RCD
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If you'd like to record watching this video as part of your continuing professional development (CPD)
Click here 👉 www.efixx.co.uk/Know%20How/rc...
CPD is a requirement for membership of competent person schemes operated by NICEIC and NAPIT
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#electricaltrainingvideos #electricians

[@kelvingomersall7460]

I will genuinely never understand why the education sector looks down on YT and lecturers using such tools. You guys are the pinnacle of electrical kmowledge (more so than some of the plebs that work with the IET). Forever thankful for you guys and your clear, precise explanations. Exceptional work as always.

[@AdityaMehendale]

Dan Gelbart, Ben Krasnow (AppliedScience), Matthias Wandel, Phil's lab, Veritasium, NurdRage, Alex Slocum (275MITx), TheActionLAb, StuffMadeHere, BreakingTaps, Adam Ragusea, Mathologer, StefanGotteswinter, ThreeBlueOneBrown, Sabine Hossenfelder, RohinFrancis (MedlifeCrisis) and many others prove the contrary. I dunno what gives you (or anyone else) this silly idea...

[@chillyspoon]

Totally agree with you Kelvin - this is a college level lecture, highly professional, going all the way to line-by-line comparison against the regulations for the geography of the target audience. Top content.

[@deang5622]

There are a large number of electricians on KZbin trying to make a buck out of it, both in the USA and UK that are supposedly qualified electricians that in fact don't even understand the basics of electricity. One I have had to correct recently did not even understand Kirchoff's current law. Another guy tried to claim that power is only dissipated in the load on positive half cycles of the AC sine wave waveform. There are too many of them. Sadly the kids watching the videos shower them with praise and walk away thinking they understand the concept explained in the video. eFixx doesn't get it right 100% of the time, but close to it, and are one of the few Electrician channels I would recommend.

[@martinnewbery3032]

What an exceedingly interesting video. It suprises me that there is no obligation on the part of appliance makers to block any DC effects that may reduce RCD efficiency. Martin.

[@gibbodive140]

These high quality, informative, understandable presentations are very often hugely superior to those we receive at training centres. I especially appreciate the personable presentation skills of Joe who covers the theory, where it relates to 7671 and what it means in practice. Thank you.

[@champagnesupernova7534]

Cheers for this, I never knew how to identify the different types of RCD's, and usually took a guess when doing EICR's.

[@efixx]

👍👍👍 Glad it's helpful! 😃

[@robertwilliams7222]

What else are you guessing when doing EICR’s🤦‍♂️

[@champagnesupernova7534]

@@robertwilliams7222 Depends what mood I'm in. Sometimes I'll guess whether there's a ring or not? And sometimes I'll guss the RCD trip times?

[@12000gp]

@@champagnesupernova7534 😂😂😂

[@nigelconnor2460]

An exceptional tutorial. Thanks Joe for your succinct and clear explanation. It was a great help when I was recently doing my 2391 and I sent it on to my classmates. The tutor also seen it and thought it was great. You and the rest of the team all have done a great job and keep up the good work. Thanks again.

[@ridetheion5584]

This explains something I had a totally thought wrong. 20+ years ago I worked at a hospital as a researcher. We had labeled socket that it was forbidden to plug in a computer. I assumed the non-labeled sockets were behind a better UPS or something to protect the computers. I would have never thought the fault protection could be compromised by the PSU 😲 Thanks 🤯

[@fqlynx]

Loving this type of content, you'll make a sparky out of me in no time.

[@efixx]

Glad it's helpful! 😃

[@johngray8798]

Absolutely brilliant explanation. Thank you.

[@eded6163]

thank you for the clear explaining, now makes sense to me, as why some RCds pass tests but still not tripping on over 30mA actuall leakage !

[@GSHElectrical]

Amazing as always Joe

[@efixx]

Cheers bud!

[@martinkelbel876]

Very informative video. The problem I see is that many online shops are confusing "type B" with "B curve"

[@tonyknight9912]

Brilliantly well explained, thank you ! As I see it the problem lies with 'normal' 13A plug connected devices being infinitely able to transport increasingly complex devices around. Such devices really need to be permanently hard wired and given their own RCD protection of a type befitting their complexity and ability to inject dc components into the ac line.

[@AviKhali]

Well explained vid. Thank you for your efforts and hardwork

[@christastic100]

Really good presentation , very informative .

[@ilyass_bouarasse]

Yeah

[@goldeagleengineering4898]

please do more and more of these educational programs. Honestly, I would pay for your programs. Have you got a patreon or funding pages ? Seriously, amazing content.

[@Mike_5]

Brilliant and very informative here and Joe and the team have obviously done their homework for this but you can see on the horizon the next edition of the Regulations requiring tighter circuit disconnect times and more discrimination of loads on individual circuits coming?

[@Dog-whisperer7494]

Great video Joe as always, excellent explanation, but in a video you did earlier last year the guy who was with you gave a live example of how DC could effect Type AC RCDs , it showed very clearly that AC type will trip but it could take as long as 190ms or more and that would mean some poor sod won’t be having a good day . Also you didn’t mention anything about RCD uplift ? . Great video as always mate 👍❤️

[@efixx]

Thanks for the comment Sean. 👍

[@PardoeElectrical]

Great video, I did the CPD and didn't do too badly, in a domestic electrical installation majority of circuits would be suited to type A and a kitchen ring/radial circuit the type F I did a little product search online, seems hager sells type F We install fusebox and they don't have anything other than type A at this moment in time.

[@efixx]

Cheers. 👍

[@rodgerq]

Will you be switching to Hager to navigate the issue 😋

[@PardoeElectrical]

I think the issue is trying to explain why it will cost £300 + to the client, as some clients would struggle to understand the safety functions of an RCD

[@rodgerq]

@@PardoeElectrical especially now with how stretched most people are.

[@micolislongis5558]

Great vid, buddy.

[@jeremykemp3782]

Fantastic info

[@eddieking7736]

I can not fathom why the latest edition of BS7671 has not banned type AC outright. It would remove potential confusion over which type of RCD to install. Here in Germany type AC has been banned in new installations for decades.

[@rodgerq]

This is the UK and we like things done how they've always been done.

[@eddieking7736]

@@rodgerq At the potential risk of electrical safety?

[@eddieking7736]

@@rodgerq or has my ironie detector failed??

[@rodgerq]

@@eddieking7736 it has failed 😋

[@eddieking7736]

@@rodgerq Yes, after my first reply that I what I had thought it must have, I have now rebooted it :-)

[@Bullwinkle39]

I think and RCD saved my cats life this morning, the RCD tripped when she weed on an extension lead

[@connclissmann6514]

Maybe the RCD saved the life of the extension lead? 😉

[@peterconnolly4608]

Was the cats antenna up or down ,

[@Bullwinkle39]

@@connclissmann6514 😂 I wish

[@Bullwinkle39]

@@peterconnolly4608 on the other side of the room I think 😂

[@Mike_5]

Cats tripping on weed is not a good thing!

[@hungrydaze]

Great job thank You! Can You please explain why a rccb has line and load connections when neither rcd or mcb need them?

[@yuriyura2023]

What type of RCCBs are required before and after AC circuits of solar hybrid PV inverter installed?

[@ambassadorfromreality1125]

Excellent explainer. If you have two consumer units with RCDs connected together with Henley blocks and one had a car charger circuit with a type A RCD would the second consumer unit also need type A fitted. I was wondering if the DC current would flow into the second consumer unit and affect the RCD

[@smiffysmiffy123]

What i dont agree with is that when carrying out an eicr to a property you can't insist of fitting Rcd protection as regs are not retrospective. This needs to be mandatory to fit Rcd protection in all installations regardless of age.

[@G6EJD]

It’s a good video, but I think you missed a vital piece of understanding as to why an RCD is set at 30mA; because a current exceeding 30mA is likely to be fatal unless it is interrupted in a very short time, followed by the need to occasionally scale RCD’s upstream (which you did cover) but then to ensure no circuits can ever come into human contact unless there is a 30mA RCD in line. Some people may be tempted to fit a 100 or 300mA RCD if they don’t understand why the 30mA protection level is required. Actually 7-8mA is often fatal for some people.

[@Chris_In_Texas]

And that is why our GFCI's here in the USA are 5mA max. 👍🤠

[@JJ-kr6ky]

4:57

[@patrickcannell2258]

These GFI are for 1 socket and local. The RCD caovers a few circuits. ​@@Chris_In_Texas

[@patrickcannell2258]

23 mA shock across a person's heart can cause fibrillation. Initial RCDs were 20mA. Nuisance tripping.

[@G6EJD]

@@patrickcannell2258 well RCD’s are set to the distribution of human survival, which can range from a low value like 15mA up to maybe 45mA with 30mS being at the centre of the normal distribution.

[@strongmanequip]

Thoughts please on the implications on RCD's upstream I will give an example of a caravan park where the caravan and the supply pillar need a 30mA RCD. What is the dissipation distance of the DC elements in a final circuit? Will both RCD's need to be type A minimum?

[@Will_I_am_-_Takeley]

Your diagram of an RCB is incorrect in that one of the coils is shown in the wrong direction. In the direction shown both the coils are magnetising the core in addition. Both the coils from the supply side should go the same way around the toroid, e.g. from the supply side go under the toroid and up through the middle. I find it easier to visualise and understand how a RCB works if it is shown as a two core cable, line and neutral, wound together round the toroid. Then visualise the magnetic field around the cable. When operating fault free there is no magnetic field around it. As the line and neutral currents are equal magnitude and opposite in direction. Thus they cancel each other out. Under fault conditions there is a magnetic field due to the difference in the magnitude of the currents.

[@efixx]

Thanks, it's more of an illustrative diagram to convey a point but we get your point.

[@deang5622]

Magnetic field representation is wrong. The field doesn't cross the centre of the ring.

[@nejendary]

how is tere not 1 mil subs yet!??!

[@IM35461]

A question for you experts. Just had solar installed and they added a Fusebox branded consumer unit with a surge device, main switch and a 16amp MCB feeding the inverter via generation meter. The board is fed from service cable connectors and home has overhead power. So no RCD of any type on the inverter. Is that allowed? The rest of the home is fed from a plastic Hager board with a 80 Amp 0.1a Type A feeding two Type AC 63 Amp 0.03a. One last question should the panels be bonded to ground in any way? Just plus and minus cable running up outside of house in 20mm conduit.

[@brianhewitt8618]

👌

[@freethink3r]

On the subject of RCD's, can you suggest a suitable RCBO for Solar PV AC circuits? Most of the manufacturers i have asked say their devices are not bi-directional and therefore can not be used with solar or battery circuits.

[@shmayazuggot8558]

I gather an RCBO is a more suitable platform for modern equipmemt including DC infiltration?

[@ralph17p]

Well - I couldn't remember what I'd chosen when my board got swapped back in 2018, so I went and had a look. Type B Hager RCBOs throughout... because maybe I wanted to leave the option open to connect an escalator to the doorbell circuit?

[@dansheppard2965]

Interesting it's still 30mA for livestock. I wonder if there are any special regs for livestock? They're definitely more vulnerable to step potentials, espceially horses and cows (so get your earth rods sorted), but I'm not sure about cardiac currents.

[@adriandunne4382]

There were several racehorses electrocuted at Cheltenham racecourse several years ago, and in Perth, Western Australia a police horse was electrocuted at the agricultural showgrounds. Both were due to old faulty underground cables presumably not RCD protected,

[@ambiencelectronica]

Which Type is recommended for Dimplex Quantum RF storage heaters?

[@lemech]

Hi, is it ok to place type A 30mA downstream of 100mA type AC RCD? Thanks

[@lourensjacobs9089]

If you have more R C Ds in the same system, how do you stop them from reacting with each other?

[@wayneh150]

Is 10ma a better option

[@AdityaMehendale]

Ehh.. a little problem: The way the coils are illustrated at 7:42 - Instead of 10A and -10 cancelling to 0A at the RCD, the way the wires are shown, the magnetic lines actually _add_ to result in 10A + 10A = 20A - this would overload and trip the sensor-coil immediately. (Apply a x-hand thumb rule, works with either hand, as long as you use the same hand in the brown and blue wires)

[@girtsziverts3530]

Ough what we gonna do now? Report to IEE and IEC immediately in written.

[@AdityaMehendale]

@@girtsziverts3530 When dealing with high EMF, it's all about attention to detail ;) One small oversight, and ZAP! Seriously, though, a diagram whose sole purpose is to explain a specific concept ought to depict that one concept correctly.

[@deang5622]

​@@girtsziverts3530 IEE doesn't exist and hasn't done for a few years. It's The IET now

[@deang5622]

7:49 The magnetic field pattern for the ring/toroid is wrong. The toroid is made of ferromagnetic material of low magnetic reluctance and the field remains inside. It does not cross the gap in the centre as that gap is made of air which has a high magnetic reluctance. The correct diagram is of two circles of magnetic field contained within the ring and passing fully through all 3 coils. And then you mark the direction of the two mag fields with arrows, which will be in opposite directions.

[@andrekhoury6252]

well im switching all breakers to rcbo type A rcbo thank god every circuit has its own neutral can u pls check geya rcbo dpn style breakers those are new and 18mm wide

[@SteveN-pw4dj]

I find it interesting the more protection we have now for electrical circuits, yet electrical fires are on the increase... I am curious as to why.

[@efixx]

More electrical stuff

[@SteveN-pw4dj]

@@efixx more battery powered stuff too I suspect, and fake electrical equipment i.e chargers and batteries

[@shmayazuggot8558]

Internet,more news b ut actually less fires

[@MegaCyrik]

My head hurts. Did you just explain my type A is ruined because it got magnetised from either my dc phone charger, my dc laptop charger, my 12v lead acid car battery charger or my 60v dc charger, or my cctv box dc charger, or dc router network charger. and now i need a new type B? Because they backfeed dc into the ac line?

[@ianmiller3182]

It's time that all appliance manufacturers specify how much dc leakage the appliance is likely to produce. The generalisation of type A being the minimum standard may not be adequate. This is beginning to look like a bit of a money spinner for the manufacturers if the regs continue to up the minimum standard leading to upgrades even if recently upgraded. Poor consumer.

[@tonypetro9945]

I'm in Korea with 220V 60hz 2P single phase on a TT, and there is no nuetral bus bar, one grounded Air Con. We have voltage ELCB, which have leakage, short circuit, over current but shouldn't by definition of ELCB not detect residual current or have overload protection. It is IEC 90947-2 Category A. Live reverse neutrals everywhere, magnetic field detectable 1 meter away from lines. I'm trying to figure out why two engineers and an electrician are just like it no problem, didn't test anything. Test switch one breaker doesn't work, romax one roof tapped together under a water bottle...no problem, What!!! I searching for why RCBO should replace ELCBs on a TT that has no nuetral bus bar. I need a visual. One of these professionals is telling me ELCB are safer and I'm like how could they even work if there is no nuetral to earth connections, there is no path..dm me I will send videos.

[@professorg8383]

I'm in the US and we use GFCIs and AFCIs. Frankly far superior to RCDs and ELCBs. But the UK guys who still allow ring circuits, will tell you otherwise!! Anyway, I'm not an expert in the IEC/EN/BS standards nor am I fan of how the IEC works as an organization. And I think its standards are far over rated. In my opinion, with decades in heavy industry, I see IEC rated stuff as "cheaply made junk", but that is largely because of comparing it to the bulletproof NEMA design specs. But that aside, from what I know about ELCBs and RCDs, ELCBs can potentially be of two basic types. One being voltage operated and one being current operated. The voltage operated being of older technology. You said you have no neutral bus so I'm assuming you have neutrals attached to the ground bus and likely the neutral is also bonded to the ground bus. But I'd have to see a diagram to be certain. I'm not really familiar with your panels. In TT systems, the neutral is grounded back on the utility side, usually at the generating station. Your initial breaker is likely the ELCB or maybe an RCD. You have to be careful watching these videos, because the exact system used in your country may not be the same. You also need to be careful about taking advice from someone not very familiar with your system. (so take what I'm saying with a grain of salt!) I would find the documentation for your particular ELCB. Then do some research comparing the ELCB type ad RCDs Look for stuff particular to your country's system. IEC likes to say it is the worldwide universal standards. Nothing could be further from the truth. Also note where the info is coming from. This channel is from the UK. The wire to the BS standard which is a UK version on the IEC/EN standards. IDK if Korea has its own version or if you just use the EN standards.

[@jeremykemp3782]

It still hurts tho!!!!!

[@MARIOista]

Hi ..I think you're wrong about using inverters in domestic appliances . You can buy an inverter washing machine or microwave . Maybe someone repairs different types of electric & electronic devices in the living room and watching football you known .....

[@slimjim2526]

Soon going to cost 3k for a new replacement distribution board, amazing that all these appliance manufacturers can leak earth faults and now dc leaking to ac and it’s ok then just your old sparks got to sort the problem out and potentially getting into trouble if he overlooks or just misses a potential problem. Can’t wait for retirement as it’s getting a joke

[@postiemania]

RCD's can and do fail, this is why they MUST be tested regularly. Most people blindly believe that the RCD will save their life 100% of the time. How about educating the public about the necessity of regular testing and inspections.