Boat house in Nottingham had a TT earth connected to the incoming water pipe which was plastic, so there was no earth for the building. But the telephone line was connected to the building earth, and earthed at the exchange building 600 yards away on the other side of the river. When an earth fault occurred in the boat house, the telephone line card caught fire in the exchange building.

I can see the TTs on the statue in the background at the start of the video

In South Africa it is common to have a earth electrode on a TNCS system, to improve the earth from the electrical supply ( the neutral is periodically spiked to earth on regular intervals on the supply side as well) So the more people spiking to earth the better the neutral connects to earth.( Less ground lift under load) RCDs were also invented in South Africa, so we have had them since the early 70s. So you don't have to rely on the earth tripping a circuit breaker, but rather the RCD tripping.

This is why it is so important to look after your TTs Pay attention to that ladies

just love John Ward Videos,, no silly speeded up nonsense and stupid muzak,, just clear explanations and live drawings and illustrations ,,,,,,, so calming relaxing also takes all the days tensions away

So with the density of modern housing its pretty much impossible to do a TT system. So I have noted that some vehicle charging point manufacturers have tackled this with PEN monitoring therefore disconnecting the supply if the CNE cable is faulty. On inverter systems it is important to be certain that in island mode these do recombine the neutral & earth connection as well as not being capable of back feeding into the network.

CAUTION! This video has wiring colours to two versions of BS 7671. Great care should be taken before undertaking extension, alteration or repair that all conductors are correctly identified.

This is the exact issue I have on a current property, house has 100A supply and TNCS, Garage which contains the boiler/water main etc. All metallic pipes supplying the house which has a 10mm bond coming from it to bond the boiler plant. However the garage (metal framed with a reinforced concrete floor which is all bonded) has a separate 100A supply which is on TT and also linked into the boiler plant because of the oil tank. Inherited system and is going to be a complete headache to sort out. Great video as always.

Sounded like an advert for the latest crazy regulations - foundation earthing.

Very clear and concise explanation. Enjoyed it JW.

Excellent explanation. I have a Tesla point in an outbuilding and the electrician installed a TT rod solely for that unit. The sockets and lights in the building use the TN-C-S ....and now I know why! Thanks.

In Ireland, a TN system comes into our house, and also an earth electrode is linked to the dis board, via a 16 csa cable, the 16 csa t/e that connects the dis board to the suppliers equipment has the cpc also connected to the neutral of the suppliers service fuse, thus TT and TN system combined

Do enjoy a Saturday afternoon lecture from JW. 😁

Can you please do a video on IT earthing system.

Thanks JW for the input 👍

I have a degree in electrical engineering and I still manage to get confused by this. Your explanation is masterful! And this is exactly what my late father-in-law did in his 18th Century farmhouse, because there were other properties close by. Glad I’m in software instead…

The ridiculous thing about the continual water supply from the house to the outbuilding is that the cross-sectional area of 15mm copper piping with a 0.7mm wall thickness is 31.4 sq mm, or three times that required for earth bonding. Why the authorities do not allow a continuous copper feed to an outhouse to count as a bonding connection, I've no idea. After all, for a TT outhouse connection, then we would have to know the converse is true; that is it is not metallic throughout its length. Where it is continuous, it's likely to have a lower impedance than any bonding cable that is put in (something readily measured as well). I think I would also argue that if you have a TN-C-S system and are bonded to metal water and gas supply pipes, they are going to provide a much lower impedance earth return path than any rod you are likely to stick in the ground as there will simply be vastly more metal surface area exposed to the ground. Of course, the regulations don't allow a TT system to use those water and gas pipes as the earth, but I suspect that where it's a TN-C-S supply in such circumstances, the reduced earth return impedance provided by an ground spike is going to be insignificant.

Why do I get the impression, that in the future, there will be an investigation into why so many people are being zapped due to the incorrect(ish) installation of car chargers.

Ham radio adds even more complexity to earthing of antennas and having ‘rf’ grounds etc

So most tt earthing systems aren’t actually tt?? I’ve tested a lot of tt systems and it is surprising how many of these systems have an unexpected low earth fault loop impedance (Zs) at the extremities of the final circuits (as good as you would expect on a tn-c-s system), due to the water and gas parallel paths that exist, obviously neighbouring properties that have had a tn-c-s conversion at some point. In all honesty I think the “convert the incoming extraneous parts” to plastic is unrealistic solution. So that leaves the question what is the real practical solution 🤷‍♂️ Great video JW👍

And another very informative video. Absolutely brilliant JW.

So when I find a bad earth connection on the supply side and the DNO tells me that an earth connection is my responsibility, but the gas supply is metallic and I live in an urban situation with all sorts of buried metallic services and variety of neighbouring earth connections, how prey do I make a compliant system for my vehicle charger or outside power point?

Great video JW. A question for you, if I may. If you were going to install an hot tub or EV charger in your home, based upon your power supply characteristics, how would you install them, to give you complete peace of mind

Thanks a lot for the nicest explanation

Thanks John Very interesting

Great videos John. The best!

Interesting! I have an odd situation in my house a previous electrician has cut of the cpc from what i believe is a TNS supply as its only something like a 2.5mm. (Cpc disappears behind the DNO wooden backboard i think the DNO head is in my neighbours house as im mid terrace and the house was built in 1950s. All i have is VIR into the meter on my side). Anyway iv done a Ze on the cut cable and its 0.28ohms but a earth rod has been installed instead of using the 2.5 as i assume it was decided to be undersized. (60A supply) iv been tempted to connect the DNO cpc into the Db to improve the current Ze and leave the earth rod in. However i figured any fault would still travel down the 2.5 as the resistance is so much lower than the rod.

I found this channel a couple of months ago and have been really enjoying it from over here in the USA! Thanks for all these videos. I'm planning to install an EV charging point sometime soon here at my home here, and your posts have raised a question for me. We have TN-C-S with neutral and earth joined at the service entrance, grounded on the property with two separate rods, and also by bonded to a metallic gas line and a buried copper main water supply that no doubt both supply their own grounding. I wonder if that difference -- having grounding present on each property -- is related to why we do not have special requirements for EV chargers to use TT grounding or to be otherwise protected in any special way. (I believe that the charging points themselves already have built in GFCI/RCD protection, but that's all as far as I know.) I wonder if our installations are inherently more dangerous than those going in in the UK, or if the better grounding, coupled with split phase 240V giving a maximum difference of 120V to ground, somehow adequately mitigates the dangers in a way that I do not understand. Maybe something to do with charging relying on the two hot wires to get 240V and not really using the neutral? It seems to me like 120V between the body of the vehicle and the ground would still be a possible failure mode, and plenty dangerous. But I'm not an electrician, and I may be misunderstanding something. Any thoughts on whether this difference in requirements is based on some mitigating factor present here in the US, or maybe just represents a different tolerance for risk or lagging standards?

Metal shipping container used as a shed with power in it, TN-C-S supply. Do you bond the container? You wouldn't bond cable tray (I don't think?), none of the electrics are directly connected to the container itself and were you to bond it and get a PEN fault the whole thing would become sizzly. I'm currently taking the view that it would be more of a risk to bond it than not, but I'm not all that sure! The workbench is probably more important to bond IMO.

Hi John, excellent informative video thank you very much. I have a question you may be able to advise, our supply in a TN earth but I have two containers sitting on the ground and a metal garage alk of which need to be earthed. Will the surface area of the structures sitting on the ground introduce a TT effect or would this be negligible. Many thanks👍

Great video as usual John 👍🏻

I'd be interested to see a video on how radio frequency grounds fit in with all this if that's something you've had any experience of. For a lot of radio transmitter systems you want a very low impedance ground. Some antennas like 1/4 wave verticals need a very good ground to drive against. This can mean burying lots of metalwork in the ground like a large mesh mat or hundreds of radials coming from the antennas base. When combined with a tn-c-s system this good ground can present a very low impedance to the rest of the street and if you're not careful you can end up sinking ground current through your radio equipment for the rest of the street. Grounding can be a nightmare for radio amateurs like myself as it can also provide a path for interference and you can end up with RF in places it shouldn't be. Then there's also the risk from lighting strikes to consider. Then there's the distance between the equipment and the ground point because at high frequencies where that distance can easily be significant compared to the wavelength of the frequency of operation and it's impedance can vary. My station isn't grounded and I use a DC power supply that's isolated from the mains. I've never had any issues but because of this I steer clear from antennas that require a good ground to operate but I should probably ground my station to protect against lighting but I'm not sure that's even realistically possible so I just disconnect my antennas

In the last scenario you described John if the neutral conductor was broken somewhere up the street surely the neighbours houses return path would then be through your TT system and potentially make all your extraneous conductive equipment live as the current rose?

Great discussion. Thank you

Hi John, I am currently excavating a 6m x 4m x 1.8m deep extension to my TN-C-S supplied house. I am adding a 393 rebar matrix before concert slab pour. After the pour I will add 100mm of insulation before adding 100m concrete. I am then building a pool that will sit 275mm away from the rebar matrix. I am sure I will get a reading of less than 4 Ohms. I plan to bond all connections to this and keep it TN-C-S

Great video John, thank you. I am now wondering though, if you're getting a low resistance to earth via a gas/water pipe, i.e.

thanks John, very interesting

Interesting video John. There is one thing though; at the end of the video you suggest that connecting an electrode that is outside of the property to the PME connection is a good idea. If the electrode cannot by accessed by persons then this is OK, but if the electrode can be assessed and electrode impedance is not low enough, then this will possibly export a raised voltage outside of the ‘faraday cage’ bonding of the property.

You are awesome coming from Trinidad

Hi John, so basically TT a hot tub in a standard house is probably a waste of time. I was always taught putting a rod in on a TNCS system would stop any tingles if you were in contact with true earth & the water. Although I do seem to remember that it was if you some distance away from the tncs earthing. Also the tech helplines still state that hot tubs should be TT’d.

Thanks for tackling this tricky & poorly understood subject John. It would have been useful to have some practical illustration of isolating the TNC-S earth from an armoured cable at an outbuilding. With all the Electrician videos we have on KZfaq, I haven't seen a single one of them demonstrate this, I haven't even managed to find a photo... I gather the most common approach is to terminate the armoured cable in a plastic box rather than directly to the "garage" consumer unit. Perhaps worthy of another video please. Another suggestion I have seen is to use a plastic step-down adapter from say 25mm to 20mm at the consumer unit. I have seen a straight through 20mm, but only as a component of a gland used in explosive environments, so too expensive to be practical. An important point that seemed to be missed in the video is that 10mm earth cable to an outbuilding (for bonding requirements) as part of an armoured cable isn't really a very feasible size as it would make for a huge armoured cable! Also worth mentioning that exporting TNC-S is more of an issue where you have a metal outbuilding, particularly if damp is a problem. Plastic vs metal accessories in the outbuilding might also be worth mentioning. Also concrete floor vs wooden floor.

So work in the caravan industry, I vist caravan touring sites, storage sites and customers homes. Every single home i visit will have the caravan or motorhome pretty much continually connected to the mains supply, many, but not all will have metal body's, all will have a metal chassis and copper gas pipes bonded to this supply via the 230 volt hook-up cable, most of these homes will be TNCS arrangements Your video indicates that officially the out let to the caravan or motor home should really be converted to a TT system which in a street is actually next to impossible 🤔

Thanks JW very informative always love your videos. I have TN-S, my Ze is 0.97 called uk power. They tested and was same unsatisfactory reading. They said its not their responsibility as it is pre 1988 and I should install an earth rod or pay them to rectify. What options do I have? Thanks in advance.

Excellent explanation, thanks very much, that’s all the things you probably can’t do, what is the answer though when someone wants a hot tub on a TN-C-S system?

I've been aware of this for a long time but recently TT systems have sort of become a protective measure in their own right for some external applications and this can only be the case if there are no metallic services to be bonded and the electrode is clear of anything connected to the network neutral. Should we have new earth type possibly TT-N ? and TT just for a clean earth (Island Earth) If the IET does this I thought of it first.

Hi John, i enjoy your videos and explanations very much, thank you. I have a swim spa in my garden, (large hot tub), it's on it's own TT. The earth rod is 13m away from my incoming supply which is a PME. Water and gas are plastic. so hopefully my TT is good. The rod tested to 53 ohm's, ground very dry. My question refers to bonding. I have introduced a set of portable aluminium steps to access the spa. They sit on "true ground" and it would be normal to be in contact with them and the water at the same time. Should these be bonded to the TT. Thanks.

Much respect John. Have enjoyed your videos and learnt a lot. Thank you. I don’t think you’ve done one about my problem though? I have a Honeywell Evohome BRD91 wireless relay rated at 5A max.. but I need it to switch 10A of under laminate heating mat. I guess I must do this by getting the BDR91 to switch a secondary higher rated relay? A tutorial on how to achieve this safely would be very useful. Honeywell Resideo won’t tell me!! Here’s hoping you might consider? Thanks John.

John what would you do in this situation? Power to a carport for some lights and sockets. The carport has a metallic frame and is part buried in the ground, the ground inside the carport has good conductivity with true earth. It is also known that class 1 equipment is to be used inside the carport. The carport is also 2m away from buried PME metalwork The house supply is TN-C-S, the 2 problems I see are: - Use the TN-C-S earth and bond the metallic frame (extraneous conductive part) using 10mm The problem being this makes using class 1 equipment inside the carport potentially dangerous due to associated risks of PEN fault. - Make the carport TT, Although due to the location and presence of buried PME metal work electrode separation and separation of the metallic frame will be under 5m therefore rendering the point of making it TT pointless?

John, very interesting, thank you. I carry out Quinquennial surveys on Churches and see it becoming common to bond the Lightning conductor to the earth on the electrical system with 10mm earth wire. In the case of many older churches where there may be only one lightning electrode on a tower or spire the ground termination of the tape is within a metre or two of the external wall. I have been told by an electrician that this is correct but it appeared to me that in the case of a strike the entire earth circuitry in the church will become live. Could you comment please and also on why TT earths on Churches always seem to be within a metre of the building?

As the water pipe comes from the main building, and as you suppose it is already bonded. Would you have to bond it again? Or could you just instead use the main earth from the cable to do bonding only?

I have an earth electrode outside my property to mitigate against pen faults as at the time the DNO cabling was over 50 years old. Thankfully all this old cabling has since been replaced with insulated 3 phase and pen.

10:35 - all well and good while the PME is intact but when the PME is bringing 70+V into the MET that water pipe will act as an excellent earth between those two installations. Ordinarily, the TNCS will give the lower resistance reading but when the PME issue arises, I can't see how that pipe is ever going to deliver anything like the 50V to earth (safe touch voltage limit). I'm still inclined to go for the TT arrangement.

I look forward to seeing CJR try to wrap his head round this 😂

Excellent video

Non electrician here. This may be a daft question but how do you measure the resistance of a TT earth? I live in France and Im pretty sure I have a copper rod in the ground. The house is 30 years old now and I'm wondering if the copper stake degrades over time, thus, degrading my path to earth. Presumably I need a Megger type tester (which I don't have)? Great vid again John, as per usual. Can't thank you enough for your clear and concise content.

If I make an earth connection to the rebar in the driveway concrete along with the TNCS Supply more than 10m away from my incomer or services connecting both with 16mm do I not limit any PD over the whole area?

Thanks for the video, always appreciated. Does someone not make an RCD type device which looks for a current >"x" in the conductor between the MET and the earth rod - and when tripped will disconnect Line and Neutral conductors?.

If the outbuilding is a Metal structure on concrete floor with incoming water in plastic pipe, what earthing arangement should be used If house has TN-c-s? And shall you bond metal structure? Thank you JW

For a 3phase and a neutral supply, which system of earthing will now be the safest to adopt ? The neutral is at a zero potential thus has not current under a balance load condition . I am thinking that a TN-C will be safer than a TT . What do you think JW ?

Help please! I had an electrician install an all metal construction, step lift in the garden. Few years on, after watching JW, i realise the armoured cable was never properly installed via a glad to the CU, nor is it possible now because the cable entry into the house is buried in the wall. It might well be a 3 core cable, not checked yet. If this appliance isn’t bonded properly, would a TT setup be useful?

Thank you for this video. Can I ask a question please - with a TT earth system, how does an RCD work? My understanding is that they need the reference to neutral to be able to trip? Many thanks in advance

Brilliant thank you.

With the current updating around the uk of both gas and water pipes to plastic, and the use of plastic water and heating pipes in the property is there any point in bonding would it not just lead to a shock point to anyone touching the bonded pipe / tap?

i have tncs connection to my house but i had it checked and the earth is 0.5ohm and not low enough. would it be ok to use my rising main and an earth electrode instead to see if we can get the magic 0.3 needed?

So if you connect a remote building to a TNCS house, you should take the earth over from the house and join it to an additional ground rod. If the remote building has a steel structure (RSJ into the ground) could that be used instead of a ground rod?

Pray tell me my good man, why does the old 1980's Tefal TV adverts spring to mind when ever I see you? Only joking big lad, keep up the good work.

Not sure the massive low resistance earth electrode would help, it might even make it worse. Your neighbours really mess everything up. If you did have shared bonded metal pipes, in the event of a fault on your neutral alone, there would still be a path to neutral via your bonding, through the shared pipes, out through their bonding and Back to the transformer through their neutral. To make a difference, the impedance of the earth electrode would have to be lower than that of the path joining to your neighbour, potentially very short if in a semi detached. On the other hand if the neutral fault occurred upstream of everybody connected to the transformer, seem like it would do more harm than good. You'd become the prime return path for the current for everybody on the street- through their bonding and pipework to your earth electrode, and back to the transformer. But then an entire street's worth of current is flowing through pipes and wires designed for one house, something they may not be able to handle. Many amps flowing through the gas main to your house continuously seems a little worrying, even the 16mm^2 conductor probably isn't rated for hundreds of amps contunuously. Worse, the connection could be good enough to mask the break, allowing it to persist for an extended period, where without, the earth impedance would be high enough to cause disruption, and a call to fix it.

So how would you argue your point to the DNO when the TNS earth connection has failed and they try an get you to install a rod, or they would be happy to charge for a new PME connection? I suppose we could argue that they took on the DNO system so they need to maintain their systems earth path that was installed so many years ago?

Very useful.

Hi John, love the content you make! Question for you: who is responsible for Earthing arrangements? I currently have an old house with a TT arrangement but wanted it changed to TN-C-S - DNO is refusing saying it's not their responsibility??

I have a question to you John. When there is a risk of EMC problems due to PWM devices like solarchargers etc we learn here (Sweden) to use armed/shielded cables and connect both shielded ends of the cable to earth with short connections to lower the impedance for high frequencies. In the case of the shed having its own TT earthing and an inverter or charger positioned there what is then your opinion about the best way to go forward when it comes to earthing? I like your tutorials!

great video. are ev chargers class 1 or class 2. I have never fitted one.

Well, I know the water supply to me is supplied via asbestos cement pipes, the HDPE stopped 50m away, leaving the old AFC pipes instead. The feed though off the fibre pipe is a corroded steel pipe, and half the underground pipe is copper or plastic, along with big chunks of the inside pie as well. Still have boned the copper sections together and to the water heater, as the inside pipes are a lot better off in copper, as it lasts so much better than the plastic, and definitely is likely to last better than the galvanised steel pipes did. Still is some steel pipe around, but lucky for me not to me, all long gone, feel almost sorry for those with the steel, as it will be expensive to replace. Still have cast iron waste pipes though in the stacks, they will all eventually be replaced with PVC when they fail, but till then they are generally in good condition for the vertical parts. the horizontal parts in the ground are vitreous clay pipes, when they eventually fail the new part of them will be PVC, except for the one section, where the replacement part will be expensive, involving hydrocracking and pulling through a HDPE replacement pipe, as this one runs under the foundations of the building. Already know which company will do this, they are good at it, and have done a lot around here.

John at 10.10 if the water pipe is bonded in the house, would it still need to be bonded again in the outbuilding? I did an EICR TNS system, outbuilding same pipe, bonded in the house but not the utility outbuilding i coded C3 as it was bonded but not in right position

I would be interested to see how I might connect a small suitcase type standby generator to a TN - C -- S system. Particularly the earthing requirements.

Hi John, great video however if you say that outhouses need to be TT due to extraneous metalwork and the need for 10mm bonding how does that relate to a hottub ? As i understand it hottubs are mainly plastic or fibre glass. Appreciate your reply. Thanks Tony

Yet another set of good reasons for not having water and gas in metal pipes. Works for me. But I rather wonder if my TT installation achieves

Am I being a bit simple here or are you saying that, roughly, all EV charging installations, past, present and future, are deficient? I've watched this and also your previous video on EV chargers and you've convinced me. I'm not an electrician but I do have experience of unrealistic requirements and the worry they cause the conscientious (but not the cowboys).

Hi John, I was wondering if large isolation transformers would be an option, although clearly would add Extra costs

Where you say you should have 10mm2 earth if you're using the house's earth for the outbuilding - what equivalent is that to the armoured sheath of an SWA cable? Say I have a 4mm2 three conductor SWA (15mm overall diameter) - is using the steel sheath good enough along with one conductor?

Would it be fair say that in a garage/outbuilding with no extraneous conductive parts it’s fine to use SWA and connect to the house TN system? Thank you for the videos and sharing your knowledge.

Presumably JW will be marketing a 15m long self-drilling earth electrode, with a 14m insulating sleeve?

really good video, But how do we stop earth loops with all the copper pipes in the group? lightning strikes in the area and current can flow from earth electrode through the house out the water pipes.

May I ask, what your views are on the A2:2022 regulation 411.4.2 (p68 of the BBB - BS7671:2018+A2:2022) please? Whereby, it is now recommended to (i.e. you SHOULD) install an additional connection to earth by means of an earth electrode (as a TT backup to the PEN)? And, with respect to outbuildings, would you still divorce the PME from the house and install a local TT, or does this now mean that you can export the PME/TT to it? Thanks.

Fantastic explanation as usual JW 👍

11:10 why can't you just do the TT and not bond the pipe in the out building? It's already bonded house-side so what's the point in bonding it again?

hi John. just a question. why cant you have A tncs on a hot tub? and why cant you have a TT and a TN or TNCS ar the same time? just curious is all.

Shouldn't the RCD to your car charger or shed trip even if the ground stake is more than 10 ohms? Is an isolation transformer to likely to fail for safety?

Would it make sense to run the last meter or two of metal pipe in plastic instead? (ref 10:55) then you would not need the bonding when it enters the out building?

TT not really an option in places where there is a dry season, we don't get any rain for up 5 months of the year and the soil totally dries out, conductivity just about zero.

I thought most modern water pipes were plastic ? Some examples / pics of incoming supply TNCS TNS and TT system would be awesome / the actual boxes. Comparing a 1930 house to a 1980 house (new build estate) 30 meters away.

You have mentioned about removing metal water pipes and preplacing with plastic. What about the water within the pipe is this not conductive and will be at earth potential ?

Is it OK to Earth TT System Nuetral Conductor at the Pole Structures

I assume that if you just added an insulated section on the pipe that feeds the outbuilding in your first example then that would be fine and you could avoid exporting the earthing system?

I believe it would be as simple as making a insulated coupling at the furthest entry point of water / gas lines. Example just after the meter when installed outside the home of course.

Why not extend the earth cable at 12:03? Let's assume we install an external WIFI router instead of an A/C condenser. That means an ethernet cable probably also runs inside and connects to other electrical equipment. Wouldn't it be a good idea to bond the earth spike to the house earth in order to prevent differences in ground potential difference? I'm asking this because I personally had wifi gear on a pole outside my house, and almost every electrical storm without fail blew ethernet ports on the routers (I was only using an earth spike for the gear and pole outside). I'm guessing I could have alleviated or prevented some of that damage if I bonded the earths, or relied exclusively on the house earthing rather than a separate earth spike?

From birth to Earth.... Another good JW production... As far as the TN thing goes... Nike make a good pair of those.

4:10 but then it can't clear faults. If you get a fault to earth in the spa then it the breaker won't trip because there too much resistance in the mass of earth for it to draw enough current to clear a fault.

In the TT system as you describe it, how are you assured that you get enough current from a fault to trip the breaker? US systems ground the neutral at the transformer, but also at the main panel. Past the main panel, everything has an earth wire that goes back to the main panel and the bonding point. Sharing a ground and neutral has been against code for probably 50 years in the US?

Do you have work shop that new qualified sparks can learn more or any le more detailed vids or books for sale