Residual Current Devices (RCD) - How they work 

This is what you get when someone who really understands what he's talking about makes video explanations: great videos. Thanks.

Excellent explanation - finally someone not faking it, but actually knows what they are talking about. Thank you ever so much

Great to listen to an expert who speaks clearly with correct pronunciation. (very refreshing). Thanks JW.

Thank you again john. I was hoping you would do a little more on 3phase RCDs , explaining the principle with a 3 phase only type and the ones with 3phase and neutral supply. It is always a pleasure to watch your videos.

Excellent!, I love the clear and comprehensive instruction in all your videos JW. Makes a refreshing change from the yadder on voluminously in the hope something remotely accurate is transmitted. Thank you.

Wish I had an electronics teacher like your good self when I was at school and I wouldnt have left with half the knowledge I needed and had to learn it again by myself later in life! Always very interesting and informative videos!

Just stumbled across this video while I have been trying to figure out my intermittent RCD tripping. It has helped enormously, thank you.

This guy should be on the TV reading the news :-) Great explanation....

Thanks for making these videos, I'm finding them very informative!

Thank you John, all your posts are informative and well presented.

Great video. Held my attention right through. Well done, could listen to you all day.

Thanks for another extremely good explanation, I learned a lot today.

Thank you! Nice clear explanation with diagrams for us visual learners! Much appreciated!

Brilliant, thorough and clear explanations in all the Vid's. Thank you JW.

Hi John. Thanks for that great explanation on how RCD works. Your tutorials are so clear and simple to understand. On a different note i would have also mentioned that RCD do have their disadvantage in that if for example the neutral wire was cut then the device would be rendered useless in operation and if someone was to touch the active to earth then they would receive a severe electrical shock. The unit would not cut out.....! Just something i would have mentioned in your video. Keep up the good work. Cheers

excellent series of video's... passed them to my apprentice saves me time thanks

What a wonderful video. Thanks John.

I always knew what they did, now I know how! kudos to you sir.

Thank you so much for this! Clear and concise! Be well, be blessed.

Very informative videos! Well done!

Thanks for this video and all your others. They've been very useful to me.

thank great explanation. i couldn't explain it better myself

Wonderful explanation sir!!!! Thanks for share this information about residual current devices also known in us as GFCI

Thank you John, have always wondered how RCB worked, and have first hand experience a few weeks ago where the newly installed consumer unit RCD tripped due to 'rain water ingress' into a light switch. I dread to think what should have happened to us or to our home if we hadn't had the CU upgraded. Than you for the clear and concise explanation.

Great explanation! Thank you!

You helped me today John. Thanks.

Thanks for sharing RCD, now i really know what it does.

Useful and easy understanding, you are so great.

Hi! Greeting from Argentina. In my country we know it as "Interruptor diferencial" or "differential switch".Excelent video!!!

In offices here, we use what we call "alamats" Which is the same thing as a RCBO it is a breaker with RCD included. Even some household installations use these.

The multiple earth neutral system is only used on land and small boats. In heavy marine applications they don't use the ships hull as an earth return because in marine applications that would cause a circuit breaker to trip and the electrical equipment to shutdown if one side shorted to the hull, also they do not want the hull to be a return path for electricity because it would cause metal electrolysis when shore power connections are made. 

Great explanation I always wondered how it worked. In my house, it says RCCB rated 100mA made by Hager

respect to your effort sr.

Your explanation is great

John That was very interesting and informative video. I wonder if you could produce video on RCBO use and operation. Thank you for all the hard work producing these video I have enjoyed watching them.

Thank you for your videos, very useful.

Very good clear information.

Thank you so much for the great informations in the video

thanks for posting this.

brilliant channel bud

awesome explanation

very good clear information

Reminds me of Kirchoffs Current Law ... the good ol' days of electronic engineering and electrical principles

Excellent. Masterclass.

great stuff

i wish i found your channel and videos earlier amazing mate youve done a great job could you do a video explaining the breakers relationship to circuits and cable calculations and power factor ratios difference in three phases ad single and motors etc please much appreciated

Had RCDs in four of the places where I've lived - there was just one, not on the lighting or heating circuits, in one place, another I think was the same. The next, none at all until the new shower was fitted and then only on the shower circuit. Two where I am now, with the lights and sockets being on different ones. My grandparents' house that they lived in for years had one fitted on a rewire in the 1980s - it frequently (but not always) tripped when my grandmother switched off the combination oven's socket, seemingly only if the oven was still warm, and it was "whole system" so it frequently meant a trip to the cupboard under the stairs in total darkness. Had they stayed there much longer I might have investigated - I suspect the socket was to blame as the same fault did not occur after they moved.

simply good... thank you.😀

haha.. I am so happy to see the BG's RCCB, Because we are the supplier in Wenzhou for BG.

Thank you, John. We just performed a few home inspections in Greece. And we came across these RCDs. And we wanted the information you just provided. Where can we find information about location requirements for RCDs? For the U.S., we refer to the International Residential Code and the National Electric Code.

Awesome info as usual! I would like to ask if you could make a small video about properly grounding an outside TV antenna. DVB-T is making its way to the rural areas here and I would like to install one but without the risk of a housefire in case a thunderstorm hits it :) Many thanks in advance!

Would like you to comment/discuss the situation that nominally-latching RCDs (especially those from 1990s with single-RCD for whole-installation) that seem to operate fine, no nuisance-tripping, within current and time limits, have an annoying habit of tripping when outside power fails any any/much load attached. Have observed this with Wylex WSES RCDs for example.

18:29 Residual Current Monitor or also called Line Isolation Monitor (LIM) . Those devices have also a earth connection (earth is not connected to the installation behind this device) and is only used for measure the impedance between each Live conductor (Phase or L1,L2,L3) and earth, and between Neutral and earth. In short, this device acts like a Ohmmeter, but on a live circuit.

This guy is a genius. He really is.

great video john. dunno if u can help on installing into rcds , I wanna install new double socket & our rcd is right above the area I want the socket to be. is it matter of feeding new wires from the rcd to new socket down below? I can't spur off another socket becos the nearest one across the other side of the room.

nice videos . many thanks

How about countries like the Philippines where sockets don't have a ground and the neutral/live can be on either pin, depending on which way you plug a two-prong lead into the wall? Can you still use these kind of plug-in RCD devices and get the same kind of safety? In another comment, you say an RCD can't work without a reference to ground but other sources online suggest it will still work.

Thanks for your sharing 👍

Thank you, but Could you explain to me " what will happen when we touch the Neutral line ( load side)? is it still working fine familiar with we touch of the Live conductor(load side). 2/ when we change the load side, L(RCCB) is connected to N load, and N( RCCB) is connected to the L(Load). is it still working fine?

Hello JW, do you have any idea why bs7671 forbids using RCDs in TNC systems? I know that it's not a perfect protection but at least would increase the safety of old buildings which don't have any earthing and bonding.

John would like to thank you for providing such good videos, is there any chance you could do a video on contactors?!

hello john i enjoy watching your video's and i have learnt a lot,i have a problem now as i bought a 3500watt inverter not a cheap one and i had a transfer 3 way switch installed 1 being the grid 2 is off and 3 being my inverter/generator anyhow as soon as i turn the inverter on my new split load consumer trips i have 2 63amp rcd 30ma.It trips when i turn the downstairs sockets on the inverter as inlet and outlet 230volt and the inlet is turned off by the breaker in my garage where the inverter is mounted i also have a earth rod ground and all my equipment is grounded DO YOU HAVE ANY IDEA WHY thanks john

Nice stick man J.W.

great video.

ok i got a interesting question. I have a rcd on my fuse box and then the manual said i should install a rcd spur socket for the electronic underfloor heating. which i realized later i don't need as fuse box has one. But what i dont understand why does the main fuse box rcd trip when i pressed the t button on the spur switch for underfloor heating. Also i have outdoor garden rcd sockets which work fine when i press the t button. Another issue i have is when i connect the yellow 110v transformer the rcd trips sometimes ?

very good video

Hi John, if the value of Ampere does not trip on overload then what is the purpose of the value in selection of my installation 20A, 32A, 40A, 63A

I'm going to get a plug in type socket tester, they don't detect Earth/Neutrl reverse, I am not sure if this is a concern? Some are a tenner and some are £20, is there a standard I need to check for before purchase? UK 240 V domestic

Hello john whether there are two CTs inside RCD connected deferentially means one CT connected at live conductor part(RCD) and other CT connected in neutral(RCD) and these both CTs connected to relay. When leakage take place current flow to the relay.?

Thanks a lot!

Ref statement at 20.04 - 100mA devices need LOWER earth loop impedance and are useful where leakage currents are higher, eg. main distribution followed by 30mA RCD at final sub circuits.

Nice video boss

Hi John, as a request, if you haven't covered this somewhere else already, wondering if you could do a vid on circuit discrimination/selectivity? Thanks

Thanks Sir for this great video. In fact, I know briefly the idea of work of the RCDs long time ago, but what brings me here is the confusion I am facing now and searching for an appropriate interpretation for. The problem is that the RCD is supposed to sense the current returned from the neutral but the question is: what about the current consumed in the load? I mean, if the supply gives 2 amps and the load consumed 1 amps and converted it into heat or light .. whatever, should not I have only 1 amps returned current? Also, I know from the university days that the neutral carries current only in case of unbalance. Of course the single phase distribution for homes out of the 3-phase source will ensure that there is a permanent unbalance in the system, but what I remember is that the neutral will return only the unbalance difference. Finally, I would appreciate if you have experience in Operation Rooms safety and how the system of earthing to the PVC and the isolating transformers are related together. Regards,

Excellent video, John. I've got several extension cables that have mains filters on them. Can these contribute in causing the RCD to trip? Thanks.

Between RCD & ELCB which one is more reliable and safer to use? I heard RCD is the upgraded version of ELCB, is that true?

Hello sir I am an electrician from Thailand. I would like to ask for information, according to the IEC standard, how long must the residual current circuit breaker be cut off?

Nice one.

Hi J W , on the R C D ,there's a diagram on the face of it , it shows 4 poles with a broken line running through the middle, my question is how can you tell what side is the supply, and what side is the load? ,great video's ,I'm really enjoying, thanks Steve

How much would you estimate the cost to change an old Wylex for shower to RCD parts and Labour any idea ?

In an off grid situation would I be able use an RCBO if I connected the neutral from the inverter to a ground?

Hi john, would an rcd still operate if there was a cross polarity?

Can you please tell me if it is possible to connect an RCD the other way around? I mean for simple circuit breakers it doesn't make any difference. Is that the case for RCDs?

John, "Im = 630 Amps" with the numbers on the face of the device. What current does that represent? (10 x device rating).

John, on a related topic, what do you consider the best means of rigging a warning buzzer for when an RCBO trips? There's a possible water ingress in our garage circuit with the very heavy downpour a couple of days ago and it tripped but now appears stable. I would like to fit a warning device. What do you think of RCBOs with auxilary contacts in order to fit a buzzer/light? If I can actually find one, that is, as I can see it mentioned online but rather difficult to find...

I almost fell asleep twice in the first 2 1/2 seconds but things really picked up

You said 100 mA RCDs are used for systems with high earth fault loop impedance. If the earth fault low impedance is high then potential leakage current is lower and in such circumstances we have to use a more sensitive RCD, which will trip for less than 30 mA, right? Could you please clarify this?

yes i design all parts for people to look at the many things what i have done. so i can learn you of things what i can do. so listing to the story are giving.

Hi JW, Why my RCD is tripping frequently during a thunderstorm??

Hi JW, Where is the practical use of RCDs having I∆n=0.3A / 300mA. Does it gives protection against electric shock.? Should it can be used for residential applications.?

Have you a video explaining how an RCD can be used where the earth looop impedance is too high. Is this an acceptable solution in a domestic situation where you do not want to install a larger cable etc etc etc Thanks

Hell Mr. John Ward, could you make a video to explain the functions of each component in RCCB, RCBO and MCCB?

thank you

Very useful, thanks. But does the polarity matter - the hager and the British General (CUR63330A) are opposite ways round?

CUR6330 technical specifications:" rated residual current making and breaking capacity I(delta)m 630 A. What does it mean :"making and breaking"?

John could you tell me if its possible to add rcd protection to a 30 amp rewirable fuse that is housed in a metal wylex consumer unit. I was thinking that if the load went through a stand alone rcd outside the board and then was connected to the existing 30 amp rewirable that might work. Your thoughts please. Mark

will electricity boxes in houses (in the UK) have RCDs in them or is it just circuit breakers.

thank u sir

@ Brent Geery The reason why the trip current is so high in the UK? Well, I'm gonna be short. Mick Jagger. Welcome to Guitland freaking electric guit boxes, axes, rock & roll man. If Mick moves to the States, the default GFCI will rise exponentially :)

Hi john, Another question. On a caravan site we connect to a pillar with our connecting leads if, for any reason, the earth in the cable or the supply pillar lost this connection to earth would the contact to earth by the caravan legs be sufficient to trip an RCD in the van under the same circumstances as my earlier post.?