Why RCDs trip when faults between neutral and earth occur, and why switching off a circuit breaker / MCB is not isolating the circuit properly.
► Support this channel:
Patreon: / jwflame
PayPal Donations: xo4.uk/?PPP
► Social Media:
Twitter: / jwflame
Facebook: / jwflame
Instagram: / jwflame
► Contact info, sending stuff in: etc.:
xo4.uk/?YTT
► Website - More on this video and many other subjects
Website: www.flameport.com
Here I am again watching this video 2 years later. You are a national treasure JW.
This used to drive me nuts in my old house. Such a simple explanation but all the same I'd have never figured it out in a zillion years. I am demystified at last. Thank you so much for this!!!
Thank you. I have always wondered why an RCD can still trip even if you have the power off on the circuit you are working on, now I know.
you have a knack of explaining stuff that even I can understand
This guy is great. So informative and explains things clearly
Thank you for explaining this so clearly. The scenario you mentioned in the first 40 seconds was exactly what happened to me today! I knew what I did - but didn't understand why this happened. Now I do - 9 years after you made the video!
Thanks for the videos John, I find them very informative, easy to understand and a great back up for my level 3 2365 . Thumbs up on every video so far. Thanks.
great video, explains what i was after. this happened to a street light while i was working on eastenders. the lamp wasnt working, it was disconnected from the supply but there was about 50v between earth and neutral. i have been trying to figure out the cause since. thats scratched an itch! cheers john, all the best.
Hi John... Many thanks for your time too explain in depth the earth / neutral faults.
Extremely helpful video as usual from John. I watched it so carefully that I noticed that you edited the video at 4:27 :) Thank you very much. You saved my day! Your video confirmed my suspicion of a N-E fault in a residential installation in which the responsible 30mA RCB was switching off every 5 minutes! despite all the MCBs switched off (and Live bus bar removed, just in case). Locating or narrowing down the fault is as easy as removing the Neutral wires one by one from the Neutral bar and see which one trips the RCD.
Absolutely brilliantly explained for a layperson to understand the basic concepts! Well done!
This guy is quality... Makes everything make perfect sense... Thanks alot John
Thank You John Word for all your lectures. you have used a simple and clear way to be understand
Thanks for doing this John - very well explained.👍
No one would fail their Electrical exams if you were the tutor. Great stuff. From a non electrical person!
This is one of the best explanatuons with demonstrations I've seen. Well articulated.
Excellent explanation, John. I see this sort of things with inspecting caravans, where the owner has wired the damn thing themselves and left the link in between the Neutral and Earth busbars at the little switchboard, that's normally in the smallest cupboard ever. It's that time of the year at the moment, considering people can't fly out of New Zealand because of Covid-19 restrictions.
You know, we're redesigning our Hackerspace's electric circuits, and your videos are very big help. :) We're situated in the buildings decommissioned bunker and thus we have only one single 10A fuse for our space and it's pretty much inadequate for our needs. All the sockets and lightning is behind that one fuse, so we're going to replace the main cable with bigger one, install bigger fuse to the other end and a consumer unit for our space so if we trip something, we don't have to walk all the way to the buildings main fuse box (that's behind locked door) to get everything up and running again. The idea is, that we design and build all the new connections etc, without making them live and then sparky with proper equipment and credentials comes up, measures and checks everything and connects it up to the mains so it's legal. But since it's been like 13 years when I went trough the courses about electric installations, it's been a good resource to remind myself about the topic. :) Luckily we have a memeber with automation as his credentials, so he's a big help even if he doesn't have the classifications of a sparky. All we need to do is to make sure, that the differences in standards between Finland an UK aren't going to be too large so our sparky doesn't get a face palm when he sees our designs. :D So thanks a lot :)
Brilliant explanation - thanks John! As well as understanding why neutral/earth shorts trip the RCD I also finally understand why the RCD has no interest in the state of the earth!
I just love the occasional dry humour, makes for interesting listening. many thanks for the detailed explanation.
Hi John, yet another very helpful video - you have a great talent for education. Thanks very much for all the time and effort you put into this Channel, cheers.
Great .. amazing video , this can be overlooked when working in the field. Thanks for uploading.
Hi John EVER So many thanks for this informative video. Now I know when cutting through a cable with the appropriate line mcb OFF, the rcd trips. Thank you again. For this brilliant video.. Please keep up the good work.
great teach ! it help me self repair the damage breaker ! thanks John Ward !
You have answered a question from years ago when I replaced a socket in my house. I tripped the RCD even though the circuit I was working on was isolated and I suspect I did exactly this. Thank you
This exact thing happened me tonight. I thought it was something to do the balance, but you explained it perfectly. Thanks.
Well this explains exactly what happened to me the other day! Great timing with the video. Thanks
This has helped massively to understand a fault that developed after getting some walls plastered. Trying to work out the fault using the MCBs alone was fruitless as the RCD would randomly trip. knowing the RCDs are double pole and mcbs are single leads me to believe something is still wet causing an NE trip. Problem is trying to work out what is wet.. Nice clear video tho!
excellent simple explaination straight to the point. thank you
Thank you so much for your videos it makes so much sense. Really interesting to understand how it all works.
Excellent video and very well explained! Thank you!
Thank you very much, that helped me to fix my fault last evening
best explanation ever. as simple as that! thank you!
Cheers. Excellent explanation. This had me puzzled while doing some electrical work up in my gran's attic, I thought she was flipping the main breaker as she's terrified of electricity. I'm cautious; test with a NCV tester then a multimeter before work especially as whoever did the wiring in that attic had no idea what they were doing, flourescent strip light in *series* with a ceiling rose (not for lack of wire, they just left the live wire flapping in the breeze),steel cored speaker wire (or something similar) hooked up to live and neutral leading to seemingly nothing, if I had to hazard a guess it was for an old doorbell and just reconnected by every contractor who did some work there, though why it is on the attic lighting circuit is beyond me. All of these things had me fairly worried about the house being plunged into darkness as I was concerned that there was a live (or intermittently live) conductor somewhere. Turns out it was neutral touching earth, which I'm sure of as I tested it twice. Measured with a multimeter and got .7 volts, guess the current was enough to trip the breaker though.
Thanks John. Exactly what I am experiencing with my oven at the moment.
clarity on a consign issue I have..Thank you so much
I faced this issue last month and was surprised that even though Sockets MCB is turned off , why does RCD trip whenever Neutral touched Metal/Earth...Thank you very much for your videos
Great informative video. Interesting to see that the cooker goes through the RCD. In NZ the cooker and hotwater cylinder don't go throught the RCD as heating elements sometimes have leakage and cause nuisance tripping of the RCD.
RODALCO2007 Virtually everything has RCDs now, as regulations require it for cables concealed in walls. The other options being to use armoured cables, steel conduit or having concealed cables more than 50mm below the surface - all of which are far more inconvenient and expensive than fitting an RCD. Cookers and similar are a problem, such as where a new consumer unit is fitted and the cooker which worked perfectly before now trips the RCD on a regular basis. Have also seen the same problem with people buying a new cooker, where it's been stored in a damp environment before delivery.
***** Thanks for your reply. In New Zealand a hotwater cylinder and range/cookers don't have to be on a RCD because of the leakage issues encountered sometimes with enclosed elements. Values are often around 10-15 kO.hms. and the element has still plenty of life left in them. The NZ standard also requires 2 RCD's at least to avoid loosing all power in the house.
greetings, I'm well late to the party here, but nonetheless I thought you would be interested to know The AS/NZ 3000 wiring rules are just about to have a new edition released, with one of the big changes being RCD everything. Every circuit needs its own individual RCD, including water heaters, ovens and cookers. One other big change is that if anyone who is working at a domestic residence needs to do work in the roof, they need to shut the power off to the whole installation which is interesting. you can follow this link for a preview of the planned revisions. www.commerce.wa.gov.au/energysafety/new-wiring-rules
We still use GFCIs at the receptacle here in the States, even though GFCI breakers are perfectly acceptable and code compliant. The big thing now here are AFCI's (Arc fault breakers). They are required at the breaker panel on almost every circuit in residential installations these days. (They've been required since 1999 in bedrooms, but now are required everywhere). I hear they aren't a requirement yet in the UK, I presume because you guys protect all cables with metallic sheathing. In any case, studies have shown that around 50% of electrical related home fires in the U.S. are a result of arc faults (series more than parralel) hence the new requirement. Here most homes use non-metallic plastic sheathing rated at 90C. While it's safe cable, it's still non-metallic sheathed meaning it is feasible that it can be damaged in the wall (errant nails or rodent chewing), thus the potential for unseen arcs which normal breakers won't detect. Some metro areas require metal sheathing for residential applications. Chicago is one city with very strict standards in that regard. (Here states and local munincipalities have the authority to override the national code with their own code). It makes sense in those areas because if one condo or apartment building burns, the whole block burns. It doesn't make as much sense in the country where your nearest neighbor is a mile away. We also have many very old homes here. It is not uncommon to see old homes with "knob and tube" wiring from the 20's. It is legal, but if renovation is done it must be brought up to code. And we have tons of homes from the 50's to 70's using wiring code from back then. Grounding has been code since the early 60's I believe, but there's still many homes out there without an earth ground circuit (all receptacles are two prong). Some unscrupulous people will install 3 prong receptacles in an old home without a ground circuit, thereby creating a "bootleg" ground. This is achieved by connecting the neutral to the metal electrical box. This will trick the inexpensive receptacle testers into reporting there is a proper ground. These cheap testers are used by most home inspectors, and creates a dangerous situation for an unknowing home buyer.
Hello, Excellent video, as usual. Could you please do a video on RCBOs, and particularly on why they have the separate white earth leads. I am a trainee electrician, and was told by one qualified electrician that they are to prevent nuisance tripping, but another qualified electrician didn't know what they were for
The white lead is an earth connection and it is usually used by the TEST function of the RCBO... which creates a deliberate imbalance to earth in order to cause the RCD part to trip. If you don't connect it, the TEST function usually doesnt work. Some RCBO's are designed so that they don't require that earth connection
Great stuff John, thanks!
I've had this happen when I made up an adapter for a caravan to run on a regular 10amp NZ socket (for the lighting and light loads). The caravan fuse box had a linked neutral and earth bar and would trip the RCD when plugged in. I had to remove (cut) the earth neutral link while still keeping the earth neutral wires connected to the plug on the caravan
cool videos John.. Very helpful information
Lovely explanation. Many thanks!
thanks John for explaining this.
Very good video as usual John
Very informative. Thank you!!
Excellent and informative videos thank you
Great video ! I just saw it and I think one solution for this is to use 2poles or 1p+n MCB s instead of 1 pole. So when you disconnect the MCB both line and neutral are off . The regulations in my country recommends to use that kind of MCB s. Of course RCBO s on all circuits is the best solution but it is more expensive.
In NL we use one RCD for every 4 MCB's. And indeed 2p RCD's. They recommend RCBO's for outdoor units like airconditioners, outside lighting and solar panels.
Where you from ? Romainia ? They use cow shit to build houses
Delivered really well. thanks alot mate.
Thanks so much , my broken underfloor heating caused me issues and was tripping the other RCD circuit confusingly, Just disconnected from the thermostat and all good now.
Excellent explanation ! Thank you
Excellent video, as usual.
Been there and done that - I was rewiring a socket and I twisted the bare ends of the cable together and the RCD tripped as explained plunging the building into darkness. The situation was only saved as I had a head torch in my pocket that I was able to find in the dark. Moral carry a torch at night particually when working on electric circuits.
Excellent explanation!
Very nicely explained.
Hi, Robert come lately! Thanks John, very clear explanation. BobUK.
Excellent explanation!!! Thank you
thanks for the vid - really helpful!
Great explanation. Thank you!
Very good explanation, thanks.
What you're saying is that double pole mcbs are the way to go (especially since they exist in slim form factors), so that I can also isolate neutrals. The system of only disconnecting the line is a pain in fault-finding
Clearly explained as always.
Excellent video very easy explanation
thank you for your lessons :)
Excellent video ! Thanks .
Thank you have really explained it very well, I think I can now solve my problem :)
John, it would be nice to include what is happening when ALL MCB's are off (no load) and the RCD still trips. e.g. there could be equipment in the circuit that carries potential even with the power off. :-)
+Sofa Soul "TheChipmunk2008" above actually pointed this out... If you have a N-E fault, and you are on a TN-S supply, then you can easily get small currents between Neutral and Earth on supply-cable (as they may have a few volts difference between them). These will still trip your RCD when power (line) applied to the primary of rcd.
Great videos John. Currently got this problem and after disconnecting and replacing all neutrals got the problem down to sockets in lounge but cannot locate where problem is by removing each socket as all wiring looks ok. Is there a possibility that it could be a faulty MCB.I am in UK. Thanks
Very informative video John, and explained extremely well.
When making alterations to a circuit covered by a shared RCD (i.e. split load board), I will now disconnect the L, N & E of that circuit to prevent nuisance tripping as well as being a means of isolation. It will need to be done for dead testing anyway!
Excellent explanation 👌 thanks. Pls John can you pls explain about generator "floating neutral and Bonded neutral".
thank you J. i suddenly have a short between E and N after fitting a new wire. Unsolved for a week now. Have to locate it tomorrow.
Great video. Thank you
This is gold!
Excellent- thank you 👍
That was really informative ... I was facing same issue . ..
One point John, in the event you're on a TN-S system, even if there's no current from the installation, you might get current flowing from the neutral to earth from other consumers on the same TN-S supply cable, even if they're down the street, or even several streets away (In that case there's zero current in the line, sometimes quite a high current on the neutral)
Isn't neutral & earth bonded where the supply enters the meter box on a TN-S system, so there really ought not be any flowing within the house from external properties.
Steve, in TN-S, neutral and earth are *separate* conductors that are only connected remote from the premises (e.g. substation). Typically, load imbalances in the 3-phase distribution network would cause the neutral to "invert", or rise slightly above earth. This is how urban supplies used to be delivered in the UK (with the separate earth soldered to the lead sheath of the distribution cable) and I can remember seeing (small) sparks when I accidentally connected neutral and earth. What you are describing is TN-C-S (formerly "PME" in the UK), in which a *combined* neutral and earth conductor arrives at the premises, then *separates* into neutral and earth conductors for the consumer. There is still the potential (no pun intended) for a dead short on one phase of the distribution network close to the premises to pull the combined conductor well away from local earth potential, which is one reason why the UK is pretty hot on bonding of plumbing and other metalwork, so that there is less likelihood of 100V suddenly appearing between your metal-bodied kettle and the kitchen sink while you are touching both with different hands. You may find the Earthing system article in Wikipedia of interest.
Thanks - I was, indeed thinking of TN-C-S.
Good explanation!
@John Ward I stand corrected. I agree there should be a common neutral bar for the neutral connection of all loads controlled by this RCD. But I believe this neutral bar should be unique to this RCD and should not be connected to the neutral bar where the incoming neutral and non-RCD loads are connected. Please confirm.
JW Ive been wanting to get a Fluke 1653B - to test systems here in the US... But now we have ARC fault breakers - will this damage the meter in anyway? I was wanting to do a trip test and get a time/ amp reading on each 120vt circuit here in the US , any advise ?
It surprises me that there seems to be few DP RCBOs available to fit into UK CU's These would seem to provide the safest isolation. Each of the Line and Neutral would be separate connections on ether the line or neutral. An inherent design flaw in the UK consumer units.
Another interesting point to make in regards to this irritation is it is far more likely to happen on a TN supply as the impedance of the earth is generally much much smaller than that of a TT. On a TT supply somewhere in the sticks where the local transformer (and ground) is miles from the house and your main earth is little more than a stick in the ground...This is far less likely to happen, if even possible in some situations. An example would be my stepfathers farmhouse that has no equipotential bonding at all because there is no gas and all local supplies come in plastic, the only earth connection is a single earth spike. So poor is the earth, I test the RCD's every single time I go there as a precaution.
I'm by no means an expert. When you say the earth is so poor. What reading would you describe as poor? Thanks
I'm always fascinated why certain countries choose to do things like this in a particular way. I don't think I know of any countries where the N is routinely fused. I do know that in NL there were one or two areas until as late as the nineties or something like that where houses did not have regular 220/230 single or three phase (220-380/230-400) feeds - they had a three phase 127V connection, where the voltage between each pair of phases would be 220. So typical circuits would be between two lives and naturally fused on both sides (which also means that any nonfunctional circuit probably still had power to it). OTOH most countries seem to leave the neutral un*switched*, like your UK example. Here in NL however we used to have assemblies of single fuse plus double pole switch per circuit, and we've now switched to breakers that thermally protect the phase and additionally switch the neutral. The N switches on first, and it switches off last. Sometimes we get 1.5 unit wide gear, with a normal as-seen-internationally 1 unit breaker plus an additional half unit switch beside, that are mechanically coupled in such a way that the breaker can trip on its own, but if you switch, you can only switch both off, or turn on just the N and then after turn on the breaker. Or the better option, gear targeted to us specifically is just a 1 unit combination breaker and switch with a single switch on the outside. (The savings in din rail space more than make up for the cost of the breakers...). Oh: our rules have been changed a decade or two ago to allow no more than 4 breakers per RCD, and a minimum of two RCDs per installation. Also, of course, to no longer allow non-RCD circuits.
It's the same here in Italy, neutral is allways switched, for me it makes sense to do that, it's more convinent to have only one RCD and then 1P+N breakers, also you are protected in evenience that L and N gets swapped somewhere, that it is possibile.
@@mernok2001 Really you don't get any benefit if you have a RCD in the circuit, the same current that passes on L must also pass on N, so even if the polarity for some reason gets swapped you are still protected from short circuit and overload, and you have the RCD that protects you from faults to earth.
superb video
Thank you John....I could never get an answer why I was getting a "tingle" from a registered 'leccy whenever i've done work on any "disconnected" circuit in my house.....plain as day now through your explanation....My "disconnected circuit" is in fact still connected!!!...in future I WILL TURN OFF EVERYTHING at the main R.C.B...I Know before anyone else chips in, yes you have to be a 17th edition certified Electrician to work on ANYTHING more than wiring a plug these days...and it is advised that even if you do that, it is checked by one!!! But in my defence I ALWAYS DO ANY WORK MYSELF & GET IT CHECKED AND SIGNED OFF (by a registered electrician) before "flicking the switch"
Clive, I don't think anything John has said would explain why your disconnected live wire would feel tingly. This may be because the disconnected live conductor was capacitively coupled to another circuit that ran alongside it for a few metres.
Good video. In Estonia the RCD is not required for entire building, it's optional for bathrooms (water heater, washing machine, optional socket by the mirror) and other moist rooms like basement.
DjResR They used to be optional here as well, but over time, more and more things have required them, and today almost all circuits in a house must have an RCD.
Thanks John 👍
You are the best. Thank you 🙏🙏🙏🙏🙏🙏🙏🙏🙏
Only one word. Class!!!!
Can you tell me how are surge suppressor installed? I mean those the look like rcd and are attached to the board. Thanks for your wonderful videos.
Really excellent video
Thanks for big bulk of information
Great video, Thanks
Very clearly explained I like this. :-)
That's why Australia uses a MEN (Multiple Earthed Neutral - A physical wire linking the Neutral and Earth Bars) links, you in a roundabout way described what the link is meant to do in that it'll allow the RCD to detect the imbalance but only on a circuit that has an active load. This has been proved as I've used it to trip an RCD when fault finding in a large board by intentionally creating that imbalance as we couldn't ID the RCD of that circuit.
Is there any way to simply determine if it's a 'neutral to earth' / 'live to earth' / 'live to neutral' fault that trips the downstairs light breaker? Cheers for advice.
An excellent explanation as always, in our house we have a single ring main serving both floors, the RCD drives me crazy. We have lots of low power devices around the house some inherently generating a little earth leakage current. Naturally it will maliciously wait until about 2:00am before it trips, to be fair there is always a good reason. (Last time it was the cordless kettle base had water spilt on it). I really should investigate splitting the supply to two rings, seems strange that a modernish 3 bedroom house would only have one....
The concept of a ring for the whole house was several decades before RCDs were in common use. As almost all circuits in a modern installation require RCDs, the more sensible solution is multiple circuits each with their own separate RCBO.
@@jwflame, the house is 1970s which sadly I regard as relatively modern. And yes having more circuits would be a great advantage, thank you for your videos, and this reply.
if i am replacing a light fitting on an individual circuit containing several lights ( and ive isolated it and made it safe) and i know its going to trip the rcd to other circuits which will bring a shop to a grinding halt, which conductor would i reconnect first to prevent it tripping and then in which order after that (to reconnect the other two). also could you explain why they are reconnected in that order. thanks John, i hope the question makes sense
Great Explanation, Thanks. Could you do a video on what exactly flows down the neutral wire in a domestic AC circuit.? Is it current plus small voltage or just current and how does the phase of that current compare with the incoming?
It is just current. The small voltage you may measure if you measure between neutral and ground. This test is usually used to verify neutral from phase. My guess for phase angle of current is that since there is only one direction of current for half of the time it has one phase and magnitude for both phase and neutral half of time and 180 degrees shift half of time each cycle.
Mr.John please help understand me. With regards to rccb that is too sensitive when lightning occurs. whether grounding is not good enough or there is another reason.