I’m an 18th edition apprentice and 3 lecturers have tried explaining this to me. Thanks for the clearest explanation I’ve had. Finally this makes sense. Thank you John Ward.
I only have experience where I can say for certain. 1. Only phase and neutral conductors are supplied. 2. No earth rods are installed at the transformers. 3. No earth rods or bonding to re-bar in the concrete is carried out. 4. Therefor this is a substandard TT system. 5. Sometimes earth and neutral are joined together making things worse. Go watch my Facebook video Samui English Electrician
What can I say John, except you have an excellent way of passing on the concepts in a simple and concise way. Call me a sado but I so much look forward to your articles.....
What a legend. I'm doing my level2 electrical installation and types of earthing arrangements is part of the installation methods unit. the diagrams used by the college were usless so thanks for this...
Fascinating overview of how the UK system approaches electrical safety. I am in the US and I can now see the advantages to our system of having a center tapped neutral on the distribution transformer secondary. The earth (grounding) conductor is connected to the neutral at the entrance to the structure and there is an earthing rod driven at the structure.
In Germany you could find TN-C (older buildings) or TN-C-S (modern buildings) are the most common systems. But sometimes you could find TT, which depends on your supplier. The buildings with TN are fitted with an additional earthing rod for the cable failure you described at 10:48 min. Formerly they used the incoming water pipe, but now the most water pipes are made of plastic and the earthing rod is placed in the ground plate of the house (newer ones) or got a separate rod. And the most building connections are three-phase-current. The three lives L1, L2 and L3 all have 230V measured against N (or PE), but 400V against each other, so you've got two voltages in your system.
Hi John, your videos are fantastic. I am currently doing a 2 1/2 week course in domestic installations - my instructor no doubt knows his stuff but dear god he does not know how to teach or communicate. I have highlighted the most important things for me to learn this weekend and you have addressed two of them in the last half an hour. Thanks!! :) *subscribed*
these videos are so helpful. I've nearly completed my City & Guilds Level 3 Electrical Installation Diploma and this content is really helping with my wider understanding and prep for exams. I like your style of explanation, thank you.
Thank you so much I'm doing my 2391 and I'm dyslexic so need as much help as possible and your teaching is amazing for me very clear and to the point thanks again 👍
Here in Norway the customer must provide an earth rod regardless of what system is being used. Even TN-C-S-systems must be connected to earth where the PEN is split to N and earth. So whatever happens to the earthing from the power company, there will be a local, good earth point.
Robert Szasz No, only the electricity supplier is permitted to do such things. Therefore you are stuck with whatever earthing system they provide, or ignore theirs and use an earth rod / TT system.
+sjokomelk Same in Finland, I think we are almost 100% TN-CS. If you have IT-system, wont that mean that an Edison-screw light socket has its threads live too? Or do you use bayonette mounts?
In Australia we have a MEN (multiple earthed neutral) system where the star point of the transformer is earthed and each house is supplied with active(s) and a neutral. At the main switchboard an earth stake is connected to the main earth terminal and a link is main to the neutral terminal. This means that any A-E faults will flow through the houses earth wires then go back on the neutral. If there is a fault with the neutral as well and it is broken then the current will flow through the earth stake to the transformer, providing the best of bot options 1 and 3 from the video.
That's the TN-C-S system. In Germany is this the most common system too. But only in houses build or modernized after 1973. Before this date TN-C was the common system, with no separate wire for N and PE. You've got only one wire for this, the PEN.
Now the PEN is in Germany allowed only if it is minimum 10mm² copper or 16mm² aluminum. But only for new installations, the old ones made before 1973 succumb to the right of continuance. But only if they are not unsafe, making massive changes (extensions for example) and if they no longer conform with the regulations that were valid during the time of installation. A change of a wall socket, lamp or a switch does not affect the right of continuance.
Just wanted to say a huge thanx to you. Very concise and descriptive and made what seems to be (sometimes) difficult to understand, understandable. Great speech and great use of visual aids. Thanx again😁👍
TN-C-S is also the standard for system grounding in the US and Canada and has been for quite some years, except it is common for the main distribution board to have its own ground rod connected to the ground bussbar. The only other difference is that the supply transformer has a 240V center tapped secondary which is grounded and the end taps providing the 2 120V hots.
I knew JW was the place to come for this information. Looks to me that in the 'absence' of an earth, the neutral simply needs to be connected to the earthing cable inside the house at the board.
Great explanation!! In the USA we have 2 hot wires 120/240 and 1 ground/neutral the grounds and neutrals are bonded inside the main panel. The nec requires 2 ground rods for each electrical panel inside the house.
It's 2 rods if you have more than 25 ohms only with 1 rod. Wrong on each panel board. I for the main, none for others as they are sub's using se-r. Unless it's an outbuilding. Still uses the se-r, but also requires the rod.
In Denmark the TT system is exclusively used. RCD are required on all installations which supply up to 20A, including old ones that was made before the invention of the RCD. It is the consumers responsibility to make sure a device has ground a connection, and it is only mandatory make the ground connection on domestic appliances.
We have been "PME'd" here but my neighbour (same phase) is TT. My neighbour's system tripped (the voltage type you mentioned)but her fault also tripped an RCD in our property. Looking at you diagram, i think i can see how this has happened. Thanks you for such a clear explanation.
Thanks for another very informative video. Could I ask a question on TT earthing systems. Is it allowed in the UK to connect the earth rod to the neutral at the customer end, and what would be the result or problem if this is done on a TT supply. I believe that doing this would only help by tieng the two together and thus reduce any problem of poor earth rod resistance.
Great video! Here in Denmark we pretty much only use the TT system. I'm not sure why... but i guess it's because the electric company like the idea that they won't have to be responsable of the PE connection.
Here in Italy we also use TT for houseolds, only industrial use TN, I thik that's because earthing, in that case, is on the customer so if earth conductor fails, the power company has no responsability.
How on earth (no pun intended) can you get proper Earth conduction in Italy with a TT system, especially when for example you live in a rocky terrain? You guys have to drill 30M deep rods or something? :P
Outside equipment/structures/caravans etc. fed with extension leads: - (Circa 12:10 mins)Surely if the Neutral conductor got broken on the consumer side of the cutout the earth conductor would still have a path back to earth (tripping a safety device RCD's etc). Whilst long non armoured leads always present a greater hazard surely only a Neutral disconnection on the supplier side would put a metal framed object at risk (and that would apply to all earthed items in the house it's just your more likely to be in good contact with the earth outdoors?
Very good. Here in Australia we use the TN-CS system but the main earthing point is connected to an earthing electrode via the main earthing conductor and to the main neutral bar on the consumer side via a link which must be the same CSA as the incoming neutral. We call this the MEN link, and the system the MEN system (Multiple Earthed Neutral) as the neutral is earthed via the MEN link and in various points back to the TX star point. The consumer main neutral therefore functions as a PEN conductor. As JW mentioned, we do occasionally get instances of open or high impedance consumer main neutrals and shocks have occurred. RCDs clearly won't open as there's no current imbalance between A and N on the consumer side. There are also hazards if consumer mains are connected with incorrect polarity but RCDs (if installed!) will open if current flows to earth in these cases. Things are easier when you have only the one system! :o)
I have TN C-S properly installed is it allowed to earth the body of the motor or the control panel earthing point as add protection I can pond it to a sticking out construction steel that I conected to the building foundation which happened to be near them
MEN is the standard here in Australia. It's a TN-CS system, with a separated neutral/earth bar arrangement, and a earth rod in the ground. We have to find resistance as low as we can get - typically 1-10 ohms. Some sites (Centre of the country - sandy country) can see earthing rods 10-15M in depth. We equipotentially bond everything to stop balance issues.
In Australia, the Multiple Earthed Neutral (MEN) earthing system is used and is described in Section 5 of AS 3000. For an LV customer, it is a TN-C system from the transformer in the street to the premises, (the neutral is earthed multiple times along this segment), and a TN-S system inside the installation, from the Main Switchboard downwards. Looked at as a whole, it is a TN-C-S system. So, normally there will be a link in between the neutral and earth bus bars behind the switchboard, as well as at the local transformer.
A Malaysia we follow UK specs most of the time (down to voltage and socket type), though most households here use TT earthing. TN systems are virtually unheard of.
At 10:46 in that instance, where you show the break, the appliance would cease to operate as there is no return path (neither N nor E). The more dangerous situation is where the Neutral circuit is broken downstream (towards the transformer) of the closest earth rod, in which case appliances will continue to operate using the E path as return, thereby putting metal appliance and metal pipe surfaces at, or near, line potential.
SSE are now installing more and more TN-S systems on new connections work. TN-S is now always used when connecting up metal clad buildings or connecting to the old PILC cables. Funny how everything seams to go full circle. As a cable jointer I personally think that TN-S is a better system. Really good vid by the way.
Thanks John , This is exciting ,I am starting to understand , may be its the white board but youve just broke a barrier . Before i know it I'll be wiring a plug !! Seriously, the other experts who try to explain should come down to our level and see what its like , its no fun down here ,but you obviously know a few thickos and kow whats required
As an ex cable jointer I actually have had a shock from the N/E conductor of a 1ph concentric service cable! The shift electrician had attended a property and said there was no incoming supply. Labour team had been told to open an excavation over the service so I could cut and test. As soon as I removed the PVC sheath, I got a rattle. The cable had been damaged nearer the service joint and strands cut, water got in and the cable blew open circuit to the joint and phase to N/E towards the house! We weren’t issued with the much hated neon testers in those days. 😊
I've seen a few You Tube informative videos but this beats those hands down in presentation skills, clarity, knowledge and video quality. You should branch out into "How to make a You Tube video"!
Re supplying outside marquees etc from a TNC-S system - the danger would only arise if that supply came from BEFORE the "C-S2 split. Provided the supply to the marquee etc. is from AFTER the C-S split all would be fine- just like stuff in your house.
Might sound daft but why do TN-S cables have a higher resistance than a TN-C-S. Surely the resistance should be very similar or do they use lower quality cable for the earth or is it just longer run?
+Scott Clewlow TN-S is usually supplied on PILC cable, which has 2 copper conductors for line & neutral, the earth is the outer lead covering with a steel tape over it, so resistance is higher. TN-C-S typically supplied on concentric, which is all copper for the line and combined neutral & earth.
Hell Mr. John, if you please could you or someone else answer me in two queries? What was the benefit (at TN-S system) of the old cables with lead shield to come directly in contact with the earth? Maybe in the case where the cable were being cut accidently the property will still had earth connection (the earth itself will connect the two pieces of the broken cable)? Also, at TN-CS system what is the reason of multiple connections (at 10:48 min) between Neutral and Ground; maybe if the cable were being cut at some point the houses that are connected after the cutting point will still have Earth Ground connection and from now on because the only return path for the current to return will be the Ground earth the result will be a breaker or fuse or RCD to triggered immediately. So in practical this a way of detection a cut cable and to avoid a house to stay without Ground Earth (PE); because of the triggering of the breakers the properties don't have electricity and consequently the electric company must necessarily to repair the break cable? Am I right in my hypothesis or I misunderstood/missing something?
Suppose I have a three-phase motor fed from a panel that has 3 phases and one grounded neutral. I then decide to ground the mass of the equipment through an earth rod (TT) in instead of using the grounded neutral from the panel. What would the drawbacks be if I decided to interconnect this earth road with the neutral from the panel (that comes from a grounded wye LV side three-phase transformer)?
It sounds like you're describing a grounding conductor off the equipment shell bonded to the neutral coming in from the utility. This is fine. If you're talking about having two separate ground references on the same equipment, this is not fine.
Had a case where a screw shorted light switch switched line to earth. No RCD. Only symptom was the combi boiler kept tripping out on flame failure. Only when the Utility room light was on (not obvious at the time...) On inspection the live was 140v above ground at the boiler- flame failure detector required more! The earth spike was underneath patio paving, and may have been quite dry... On bright days there was no fault to find!
great video, very clearly and well explained. However 2 points. Most of Northern Ireland (rural areas) are still in TT. My house built in 2006 was done in TT. Also when you say neutral is the same potential as earth. Must be remembered that in an AC system half the voltage is carried in the neutral and the lifter you get when you accidentally touch between neutral and earth is worse than live to neutral (or at least always feels much worse!) Overall, well done.
For a commercial building, where the transformer is a private property, will the earth cable from the transformer be connected to the main earthing terminal inside the main distribution board for a tns system? please clarify. Here in pakistan the mdbs are generally earthed by two earth rods...
Muhammad Farooq Fun fact : In Italy, Spain, Greece, Serbia, Croatia, Albania, Bulgaria and Romania, if you want to make a contract with the pieces of shit known as enel, you would need to buy yourself a transformer and then give it to them for free (as part of the contract you make with them). And most of the time they will be the only option... because they are a regional monopoly... 100% unregulated free market and capitalism go so well together !
Great Video John, thanks a lot!, may I ask please - For TNS system, since both Earth and Neutral cables are connected to each other in the transformer side, why does i cannot measure continuity between both cables in my Electrical panel Distribution Board?! This kinda freak me out kindly help! thanks
drich modina There should be continuity between N &E - if not, either the earth is defective, or you are measuring in the wrong place, such as after the main switch when it is off.
***** i measured it in our 63A 3 phase with 1 phase branch distrubution board. I also thought that if i measure continuity between earth and neutral there. Most likely the RCD will trips. Please please teach me where to measure it properly and why does the RCD dont trip if the two cables have continuity. Thanks a lot in advance!
Here in the land of convicts and sea front properties the neutral wire often corrodes off in the outside connection box, we almost exclusively use M.E.N same as your TT supply but each customer has a removable link between the neutral and earth in the consumer unit for testing, this provides a limited path to the transformer when the incomming neutral fails.
There is a label on the cutout here that says "This installation is connected to a PME system" - so that confirms mine. A house we lived in before had a plate on the cutout saying "PME system" too. However, we also lived in one house where the supply came in from the poles, and that was TT. Our ELCB was a Chilton voltage-operated one.
Here in Germany we use TN-Net, TT-Net and IT-Net. The TN is splittet into TN-S, TN-C and TN-S-C. We use normal 3 L Phase, some old houses have only one L Phase. The power cable come in house direct into a big fuse for every phase - at this point the 'Saved Earth' and 'Neutral' go to two difference lines. This place is the exchange point between the power company and my home power net. After this I must install the Watt-Meter from my power company. After this we can install every RCD how we want use ... Most older installation haven't one. For Thailand I not know the situation, we use there an own transformator ...
We use TN-CS in the US but we additionally attach a bare wire from a ground rod at the electric meter to the earth terminal in the fuse box. We also run a bare copper from the rod to the nearest hose bibb, I think for discharging lightning. The plumbing would provide a path thru to the utility's piping system which used to be metal. It's probably changed since plastic supply pipes were introduced. Wait, many pipes from the 60's were asbestos-cement which i wouldn't think was conductive so I'm not sure of the system. They may have terminated with a ground rod at the water meter in that case.
im building a steel deck around my pond which will take the mains input while we start constructing our container house. they show the tncs system on the consumer board diagram but in thailand street cables get damaged all the time. im not happy with tncs so im going to ground rod the consumer box, the deck and earth all the 2 wire appliances. the water table is 1m below ground. any input on this would be appreciated.
What I'm struggling with at the moment is on TNCS how come the Neutral voltage isn't going straight to Earth at the property? With the E and N joined at the property surely the return would go straight to earth rather than back to the Transformer. It would be like you're sticking the N into the ground. Or have I missed the point?
Yes, N&E are connected at the point they enter the building. You should also get continuity on TN-S, as although the wires are separate, they are still joined at the transformer.
There is another type of Earthing that you could of included. It is called PNB. Normally used for one domestic supply only to a single phase 11kv - 230 transformer where the earth for the transformer is via the neutral block on a 100 amp cut out connected by a 32mm covered copper wire to earth electrode/pin in the ground. Although historic, lots still exist and are in use in Dorset/Wiltshire/Hampshire and Somerset.
Neutrals carry current in normal operation, a separate earth does not. If the earth/neutral were combined in the wiring, any break in the neutral would result in dangerous voltages on any exposed metal equipment. A combined neutral/earth system is called TN-C, but is not permitted in the UK.
Hi, i have a 1900s house with a lead cable , 3 cutouts (only one in use) and a green earth cable running to a small side box( i think the whole assembly is tar filled)..my house is wired in pvc coated twin and earth...mostly grey, some white...everything works fine. my question is...there is a green earthing wire in the kitchen not attached to anything and one in the bathroom also...should i clamp them to a cold water pipe or just remove them, many thanks colin...
15:30 How did you get the theoretical max loop Z of 1600ohms (1.6Kohms)? If the trip current is 30mA and assuming 230V, the theoretical max loop impedance by V/Z = 230V/30mA ~ 7.6Kohms = 7600ohms. (Which is of course even more colossal and common sense dictates that's not a good idea in practice!)
+Arglwydd Anfradwrus It's 50 volts / 30mA, as in regulation 411.5.3 If 230V was used, this could result in voltages up to that level appearing on exposed conductive parts before the RCD operated, which would be a serious shock hazard.
Ah, thank you. I stand corrected. 50V/30mA = ~1600 Ohms, but of course that's still way too high. I wasn't saying it was right for it to be 7K+, just wondered how you got that figure of 1600 ohms. Very good explanation.
JW, in the first section in your drawing you show the earth connected to the neutral on the transformer output coil or winding. But this is AC current. So as soon as the polarity changes (50 cycles per second) the positive 230vac is now connected to the earth creating a short to ground?
No, the only connection to ground is that single wire between ground and one side of the transformer. Whether that side is negative or positive doesn't matter, it's only negative or positive when compared to the other terminal. Imagine the transformer is a battery. You can connect negative of the battery to ground - nothing happens. If you swap the battery terminals so positive is connected to ground - nothing happens. A short circuit can only occur with a connection between both terminals, or between ground and the terminal not connected to ground.
Hi john I'm currently doing C&G 2365 and have been asked to give drawn examples of Tns, tncs, tt and IT supply and earthing systems. I have no problem with the former three but the IT system is proving problematic to gather info on. Do you know when or where people get trained in this type of install? My 2365 textbook states. IT and TNC systems are not included in this course so there is no information included on these type of installations. Thanks. Phil.
+phil Harvey IT is where the supply is isolated from earth, such as an isolating transformer. Neither side of the supply is connected to earth, or it is connected to earth through a high impedance. It is typically used for medical installations such as operating theatres. TNC is a system where the neutral and protective conductor (earth) are combined into a single conductor within the installation, so only 2 wires to each item. It is specifically prohibited other than in a few very specific instances, so in reality is never used in the UK. The supply is the same as TNC-S, except that there is no split to separate earth and neutral where the supply enters the building, it continues for the whole installation with the combined neutral and protective conductor. There is some information on both in BS7671.
One point you didn't mention. If you are far enough away from the transformer, the voltage drop on the lines can be significant. Where I used to live voltage available sometimes dropped below 200v. That meant the Neutral was no longer zero, and could be anything up to 20 volts above earth. Even in my last house there was enough voltage on the Neutral to trip the RCD.
Hi John, Great video. Regarding the TT earth, in the event of fault (phase+ground connection) does the current literally “flow” from the consumer rod through the mass of earth and to the transformer rod? Or is it the case that the amount of current that would flow to earth, would be basis the potential difference between the two rods? Trying to get my head around current travelling through physical earth? Obviously this is AC, so the current would be oscillating. Thanks.
Yes, the current flows through the earth itself from one earth electrode to the other one. Most of the resistance is at the electrodes themselves, the contact area between the metal and the surrounding soil is the most significant factor. The resistance of the earth isn't particularly relevant, and doesn't change much with distance. It's a similar situation to an infinite grid of resistors all connected together as described here: www.mathpages.com/home/kmath668/kmath668.htm although in 3 dimensions rather than just two.
Hi John, not sure if I'm missing something. where TT systems are in use, is there a reason the distributor cant fit a TNC-S cable head and make it a TNC-S System instead of using TT systems with high impedances and all of the other problems they bring?
@@jwflame cheers for the reply, just wondered as it seemed undesirable to be installing systems with such high Impedance values and having to install RCDs for fault protection etc
we have a Wooden Electricity pole outside our house and down the side of the wooden pole runs a thick black wire (the black seems to be just plastic insulation and where the insulation has brocked away you can see the Thick wire which is silver and not copper coloured), and its tapped to what looks like the Neutral wire on the pole and then the wire just goes either into the ground oif the property, or goes to the meter box on side of wall of property. - This is all put on the electricity supply board not on the consumer side of things. So does this mean the house/premises still has to have one or more earth rods even with this earth wire tapped to neutral line from the wooden pole? - or have the electrical supply board supplied to required earth protection to the house? - the house/property is in the republic of Ireland by the way, just in case the electrical supply is distributed differently to the UK.
If you like this topic , watch a video entitled "EW rice interviews Elihu Thomson " he's the engineer that came up with earthing " and maybe some others around the same time . Go to around 10.27 in the video and he states it was his invention for safety . I like the term you English use "Earthing " ,better than what we in the States use " Grounding " great video ps Mike Holt has good videos on this topic.
In bulgaria we use shuko plugs and we rearly have separate earthing wire.In the wall socket we just put a bridge(copper wire) between earth and neutral and it works nearly all the time.
Very well explained, one query, for PME System you said that if the neutral (neutral and earth) breaks, it will be dangerous situation because no earth is available. My question is, if a neutral breaks, there will be no supply left because to complete a simple circuit we will need to have a connection of both Live and Neutral. so there will be no current flowing through and have no danger as there would be no supply. can anyone please explain?
In trinidad we merged the TT with TN-CS connection so we put a ground rod in the installation using the TN-CS configuration so is it ok to say we use TTN-CS configuration
Question: you say that the current returns to the transformer? I was under the impression that it just kind of dissipated into the mass of the ground? By what process does it return to the transformer?
Gustav Joncus The ground is conductive, and provides a path for the current just as any other conductor does. The only difference is the ground has a larger impedance than a copper or other metallic conductor.
John can you answer a question please? Why when I changed a plug socket front that was cracked, Did I receive a "tingle" from the neutral wire around 30 volts or so, I've had 240 volts a couple of times so I know what that feels like!!! Not that I go out of my way to get it!!! ( Downstairs M.C.B turned OFF for downstairs ring main) But upstairs left on. No I'm not a qualified 'Leccy with 17th Edition but I have worked with an 'Leccy before and I'm very careful about the "quality" of anything I install, hope you can answer thanks Clive
Clive Clarke-Watson Several possible causes such as: neutral can be above earth potential on some TT earthed systems, or TNCS with defective earth, or some incorrect interconnection with another circuit which was still powered.
Thanks John, It is a local authority house built in the early 50s of the Airy type, but has be rewired and has M.C.B board I guess about 25 years ago, It even has all 3 phases into the "board" side (but only one is tapped), Would you as an Electrician be unduly worried if you came across this issue in a house that you were working upon of this age? Just would like to know so I can highlight this to the local authority if you think there is a possible wiring fault. Cheers Clive and keep up the interesting Video's!!
I always wondered how a path from live to earth was created. I thought it was an enormous earth rod at the power station. Another question, I have a 25m 15a extension cable going over to my shed for charging an electric car. Should I also put an earth rod in the shed and connect it to earth on the extension cable? I was worried the cable might be too long and the car might have a problem with the earth not being good enough. I don't have the car yet.
Shaun Dobbie Very unlikely that an earth rod would be needed. Electric cars should have a dedicated charging point connected to fixed wiring, as the charger units which plug in to normal outlets will typically take a very long time to charge the car. Extension leads are not designed for permanent installations.
Unfortunately, its my only way to charge. I think it takes 10 amps maximum but the voltage drop of the cable might be too much. It is about 8 to 10v of drop using a 2kw fan heater.
I will just have to give it a try I suppose. The evse with the BMW I3 gives you 3 charge rates. 6 amps is the lowest. If it doesn't work at 10a, I will replace the extension with 6mm twin and earth armoured cable.
The electrical supply is explained wonderfully. My thought is: if we do without grounding, the power supply will be similar to safety Tafo. Wouldn't that be much safer? Unless someone touches the L and N lines directly. Grounding causes more problems is my opinion.🤔
It's safer but only until some fault to Earth occurs somewhere - it's then an uncontrolled earth referenced system. Isolated supplies have their uses, but only in strictly controlled and monitored environments.
Hi John - Great videos, very informative - On this subject, on my house I seem to have a mixture of TN-S and TN-C-S. It looks to me as though the DNO have installed two cables in the TN-CS arrangement, and then AN OTHER has popped in an earthing rod for good measure (on a piddly little cable I may add). Would this be problematic at all do you think?
GREAT VIDEO....Hi john, recently visited a rural property TT supplied overhead 2 wire supply. where an electrician had found a voltage 54 v between earth and neutral. When installing a shower circuit. But could not find cause of the problem. Pulled the cu to bits and was left stumped. I myself called and isolated the installation and conducted tests at the distributor s supply only. I found a voltage of 280v to the property's electrode, which my meter could not perform a EFLI test on. Also I found a voltage of 54 volts between n+e. I put this down to distributors issue, as a visual inspection in the cables showed cables running some distance and twisted together for a section on the way back to the transformer. Opinion please john thank you
@jwflame With a broken PEN in the TNC-S arrangement, can't the contact voltage be minimised between exposed conductive parts and the general mass, by adding an earth electrode which will connected to the consumer's MET?
Hi, on a tt system what is to stop someone simply linking their main earth to the neutral instead of installing a rod and putting up with high earth loop impedance? Just curious Thanks
This is what we have in Greece as well and I am under the impression that by law all buildings should also have a grounding rod that connects to the provider grounding cable.
Hi John Ward,nice video. I would like to know if you could perhaps explain how one would go about choosing which type of supply to use. If you designed an installation from the ground up.
There isn't really any choice - you get what is provided by the electricity suppler, which is usually TN-C-S on newer installations and TN-S on older ones. The only choice is to not use the supplied earth and make it TT - but that is significantly inferior for most applications, so unless it's a specific situation where TT is required, you just use whatever is provided.
John Ward thanks John and what type of applications would one expect to use a TT type system. I know IT systems used in medical locations for reasons i think of no earth fault tripping the supply to the entire installation.but TT im still unsure of where one would prefer that system.
Hi John, I stopped the video at 2:45 'cause I was shouting at you! The mains transformer secondary winding can't be 230v one side and zero at the other since each side oscillates between 0 and 230v 50 times per second. Shorting one side to earth would strap both secondary winding terminals to zero, just before the input fuse blows... :-( Tim.
JW, could you expand further as to the earthing of a portable generator please? I use a 1kw Honda invertor generator on board our boat, generally for battery charging only. It represents a particular problem as afloat there is no possibility of an earth connection. The boat has a 240v shore power circuit on board which is generally connected to the mains supply in the marina when in the home berth. But when away cruising I plug the generator in to the shorepower inlet socket. Other boat users have suggested that the generator to boat shorepower connection cable should connect neutral to earth, infntbkniw what the thinking is behind this suggestion. Your videos are very useful indeed - keep them coming. Many thanks, Rob
I’m an 18th edition apprentice and 3 lecturers have tried explaining this to me. Thanks for the clearest explanation I’ve had. Finally this makes sense. Thank you John Ward.
just wanted to say thank you for providing one of the most concise and clear explanations of earthing structures
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I only have experience where I can say for certain.
1. Only phase and neutral conductors are supplied.
2. No earth rods are installed at the transformers.
3. No earth rods or bonding to re-bar in the concrete is carried out.
4. Therefor this is a substandard TT system.
5. Sometimes earth and neutral are joined together making things worse.
Go watch my Facebook video Samui English Electrician
As they say...a drunk could understand that John...couldn’t be clearer...excellent. Thanks.
What can I say John, except you have an excellent way of passing on the concepts in a simple and concise way. Call me a sado but I so much look forward to your articles.....
What a legend.
I'm doing my level2 electrical installation and types of earthing arrangements is part of the installation methods unit. the diagrams used by the college were usless so thanks for this...
Fascinating overview of how the UK system approaches electrical safety. I am in the US and I can now see the advantages to our system of having a center tapped neutral on the distribution transformer secondary. The earth (grounding) conductor is connected to the neutral at the entrance to the structure and there is an earthing rod driven at the structure.
Your videos are so thorough and articulate the subject very well.
In Germany you could find TN-C (older buildings) or TN-C-S (modern buildings) are the most common systems. But sometimes you could find TT, which depends on your supplier. The buildings with TN are fitted with an additional earthing rod for the cable failure you described at 10:48 min. Formerly they used the incoming water pipe, but now the most water pipes are made of plastic and the earthing rod is placed in the ground plate of the house (newer ones) or got a separate rod. And the most building connections are three-phase-current. The three lives L1, L2 and L3 all have 230V measured against N (or PE), but 400V against each other, so you've got two voltages in your system.
In Finland TN-C was also common earlier but after 1989 it was allowed only with a 10 square mm PEN-wire.
@@okaro6595 Same thing here, PEN only permitted if it's at least 10mm² copper or 16mm² aluminium.
Thanks for explaining the types of Earthing systems , Everyday is a electrical learning day!
Hi John, your videos are fantastic. I am currently doing a 2 1/2 week course in domestic installations - my instructor no doubt knows his stuff but dear god he does not know how to teach or communicate.
I have highlighted the most important things for me to learn this weekend and you have addressed two of them in the last half an hour.
Thanks!! :)
*subscribed*
This is a fantastically straightforward and clear explanation of earthing. Thanks a lot, JW
these videos are so helpful. I've nearly completed my City & Guilds Level 3 Electrical Installation Diploma and this content is really helping with my wider understanding and prep for exams. I like your style of explanation, thank you.
Thank you so much I'm doing my 2391 and I'm dyslexic so need as much help as possible and your teaching is amazing for me very clear and to the point thanks again 👍
A clear presentation style going straight to the key points- a very refreshing change from some of the other vids I have seen! A thumbs up from me!
Clearest presentation I’ve seen on this topic.
Probably the best explanation I have seen. Thank you.
Thank you Mr. Ward even though i reside in the states your vlogs help me immensely.
Here in Norway the customer must provide an earth rod regardless of what system is being used. Even TN-C-S-systems must be connected to earth where the PEN is split to N and earth. So whatever happens to the earthing from the power company, there will be a local, good earth point.
sjokomelk That is also permitted in the UK - however it is not required, so is almost never done in reality.
***** in a T-T system can you bond the earth and neutral at the premises demarcation?
Robert Szasz No, only the electricity supplier is permitted to do such things. Therefore you are stuck with whatever earthing system they provide, or ignore theirs and use an earth rod / TT system.
***** Although sometimes you can call the DNO out for them to convert a TT system into a TN-C-S one, albeit at a cost.
+sjokomelk
Same in Finland, I think we are almost 100% TN-CS.
If you have IT-system, wont that mean that an Edison-screw light socket has its threads live too? Or do you use bayonette mounts?
In Australia we have a MEN (multiple earthed neutral) system where the star point of the transformer is earthed and each house is supplied with active(s) and a neutral. At the main switchboard an earth stake is connected to the main earth terminal and a link is main to the neutral terminal. This means that any A-E faults will flow through the houses earth wires then go back on the neutral. If there is a fault with the neutral as well and it is broken then the current will flow through the earth stake to the transformer, providing the best of bot options 1 and 3 from the video.
The best system
That's the TN-C-S system. In Germany is this the most common system too. But only in houses build or modernized after 1973. Before this date TN-C was the common system, with no separate wire for N and PE. You've got only one wire for this, the PEN.
There are some pen systems in Australia but it's not very common and only in particular circumstances
Now the PEN is in Germany allowed only if it is minimum 10mm² copper or 16mm² aluminum. But only for new installations, the old ones made before 1973 succumb to the right of continuance. But only if they are not unsafe, making massive changes (extensions for example) and if they no longer conform with the regulations that were valid during the time of installation. A change of a wall socket, lamp or a switch does not affect the right of continuance.
Excellent video, for the first time really understand the three different earthing systems. Please keep up the good work!
Just wanted to say a huge thanx to you. Very concise and descriptive and made what seems to be (sometimes) difficult to understand, understandable.
Great speech and great use of visual aids.
Thanx again😁👍
TN-C-S is also the standard for system grounding in the US and Canada and has been for quite some years, except it is common for the main distribution board to have its own ground rod connected to the ground bussbar. The only other difference is that the supply transformer has a 240V center tapped secondary which is grounded and the end taps providing the 2 120V hots.
I think termed as single phase 2 hot wires?
@@johnburns4017 It's more commonly called split phase.
I knew JW was the place to come for this information. Looks to me that in the 'absence' of an earth, the neutral simply needs to be connected to the earthing cable inside the house at the board.
Thank you. I've been searching answers about this for long time and now got them from you. I enjoyed your video.
Great explanation!! In the USA we have 2 hot wires 120/240 and 1 ground/neutral the grounds and neutrals are bonded inside the main panel. The nec requires 2 ground rods for each electrical panel inside the house.
It's 2 rods if you have more than 25 ohms only with 1 rod. Wrong on each panel board. I for the main, none for others as they are sub's using se-r. Unless it's an outbuilding. Still uses the se-r, but also requires the rod.
In main land Europe it is more common with 3 phases + neutral configured in a star system. 400V between phases and 230 between phase and neutral.
Currently studying 17th edition and the earthing had me baffled but your video has cleared that up, great vid thanks
did you make it?
I commend you on the simple and clear demonstration of the variable systems. Well done.
In Denmark the TT system is exclusively used. RCD are required on all installations which supply up to 20A, including old ones that was made before the invention of the RCD. It is the consumers responsibility to make sure a device has ground a connection, and it is only mandatory make the ground connection on domestic appliances.
I live in the UK. Our earthing system is TT. Our house was built in the late 1960s.
We have been "PME'd" here but my neighbour (same phase) is TT. My neighbour's system tripped (the voltage type you mentioned)but her fault also tripped an RCD in our property. Looking at you diagram, i think i can see how this has happened. Thanks you for such a clear explanation.
Thanks for another very informative video. Could I ask a question on TT earthing systems. Is it allowed in the UK to connect the earth rod to the neutral at the customer end, and what would be the result or problem if this is done on a TT supply. I believe that doing this would only help by tieng the two together and thus reduce any problem of poor earth rod resistance.
Great video! Here in Denmark we pretty much only use the TT system. I'm not sure why... but i guess it's because the electric company like the idea that they won't have to be responsable of the PE connection.
Here in Italy we also use TT for houseolds, only industrial use TN, I thik that's because earthing, in that case, is on the customer so if earth conductor fails, the power company has no responsability.
How on earth (no pun intended) can you get proper Earth conduction in Italy with a TT system, especially when for example you live in a rocky terrain? You guys have to drill 30M deep rods or something? :P
Thank you.. your videos are helping me massively with retraining as a sparky.
I really appreciate you doing this for others to learn from :)
Another great video. Comprehensive, clear and concise.
Outside equipment/structures/caravans etc. fed with extension leads: -
(Circa 12:10 mins)Surely if the Neutral conductor got broken on the consumer side of the cutout the earth conductor would still have a path back to earth (tripping a safety device RCD's etc). Whilst long non armoured leads always present a greater hazard surely only a Neutral disconnection on the supplier side would put a metal framed object at risk (and that would apply to all earthed items in the house it's just your more likely to be in good contact with the earth outdoors?
Very good. Here in Australia we use the TN-CS system but the main earthing point is connected to an earthing electrode via the main earthing conductor and to the main neutral bar on the consumer side via a link which must be the same CSA as the incoming neutral. We call this the MEN link, and the system the MEN system (Multiple Earthed Neutral) as the neutral is earthed via the MEN link and in various points back to the TX star point. The consumer main neutral therefore functions as a PEN conductor. As JW mentioned, we do occasionally get instances of open or high impedance consumer main neutrals and shocks have occurred. RCDs clearly won't open as there's no current imbalance between A and N on the consumer side. There are also hazards if consumer mains are connected with incorrect polarity but RCDs (if installed!) will open if current flows to earth in these cases.
Things are easier when you have only the one system! :o)
when he said hello I'm JW.. you most certainly are John Wick with this... You my friend deserves a seat at the High Table. 👏👏👏👏
I have TN C-S properly installed is it allowed to earth the body of the motor or the control panel earthing point as add protection I can pond it to a sticking out construction steel that I conected to the building foundation which happened to be near them
Bless you dude, I thoroughly enjoy watching your tutorials. They're very easy to digest. 😉
John, many thanks again for an very clear exposition. Well done.
MEN is the standard here in Australia. It's a TN-CS system, with a separated neutral/earth bar arrangement, and a earth rod in the ground. We have to find resistance as low as we can get - typically 1-10 ohms. Some sites (Centre of the country - sandy country) can see earthing rods 10-15M in depth. We equipotentially bond everything to stop balance issues.
The explanation at the beginning, about the transformer grounding cleared up so many questions for me, thank you
In Australia, the Multiple Earthed Neutral (MEN) earthing system is used and is described in Section 5 of AS 3000. For an LV customer, it is a TN-C system from the transformer in the street to the premises, (the neutral is earthed multiple times along this segment), and a TN-S system inside the installation, from the Main Switchboard downwards. Looked at as a whole, it is a TN-C-S system. So, normally there will be a link in between the neutral and earth bus bars behind the switchboard, as well as at the local transformer.
A Malaysia we follow UK specs most of the time (down to voltage and socket type), though most households here use TT earthing. TN systems are virtually unheard of.
At 10:46 in that instance, where you show the break, the appliance would cease to operate as there is no return path (neither N nor E). The more dangerous situation is where the Neutral circuit is broken downstream (towards the transformer) of the closest earth rod, in which case appliances will continue to operate using the E path as return, thereby putting metal appliance and metal pipe surfaces at, or near, line potential.
SSE are now installing more and more TN-S systems on new connections work. TN-S is now always used when connecting up metal clad buildings or connecting to the old PILC cables. Funny how everything seams to go full circle. As a cable jointer I personally think that TN-S is a better system. Really good vid by the way.
Thanks John , This is exciting ,I am starting to understand , may be its the white board but youve just broke a barrier . Before i know it I'll be wiring a plug !! Seriously, the other experts who try to explain should come down to our level and see what its like , its no fun down here ,but you obviously know a few thickos and kow whats required
As an ex cable jointer I actually have had a shock from the N/E conductor of a 1ph concentric service cable!
The shift electrician had attended a property and said there was no incoming supply. Labour team had been told to open an excavation over the service so I could cut and test. As soon as I removed the PVC sheath, I got a rattle.
The cable had been damaged nearer the service joint and strands cut, water got in and the cable blew open circuit to the joint and phase to N/E towards the house! We weren’t issued with the much hated neon testers in those days. 😊
Should have said the phase wasn’t open circuit, just the ne.
I've seen a few You Tube informative videos but this beats those hands down in presentation skills, clarity, knowledge and video quality. You should branch out into "How to make a You Tube video"!
Re supplying outside marquees etc from a TNC-S system - the danger would only arise if that supply came from BEFORE the "C-S2 split. Provided the supply to the marquee etc. is from AFTER the C-S split all would be fine- just like stuff in your house.
Might sound daft but why do TN-S cables have a higher resistance than a TN-C-S. Surely the resistance should be very similar or do they use lower quality cable for the earth or is it just longer run?
+Scott Clewlow TN-S is usually supplied on PILC cable, which has 2 copper conductors for line & neutral, the earth is the outer lead covering with a steel tape over it, so resistance is higher.
TN-C-S typically supplied on concentric, which is all copper for the line and combined neutral & earth.
Hell Mr. John, if you please could you or someone else answer me in two queries? What was the benefit (at TN-S system) of the old cables with lead shield to come directly in contact with the earth? Maybe in the case where the cable were being cut accidently the property will still had earth connection (the earth itself will connect the two pieces of the broken cable)? Also, at TN-CS system what is the reason of multiple connections (at 10:48 min) between Neutral and Ground; maybe if the cable were being cut at some point the houses that are connected after the cutting point will still have Earth Ground connection and from now on because the only return path for the current to return will be the Ground earth the result will be a breaker or fuse or RCD to triggered immediately. So in practical this a way of detection a cut cable and to avoid a house to stay without Ground Earth (PE); because of the triggering of the breakers the properties don't have electricity and consequently the electric company must necessarily to repair the break cable? Am I right in my hypothesis or I misunderstood/missing something?
Don't concern yourself with British electrics if you can't even speak the language.
Suppose I have a three-phase motor fed from a panel that has 3 phases and one grounded neutral. I then decide to ground the mass of the equipment through an earth rod (TT) in instead of using the grounded neutral from the panel. What would the drawbacks be if I decided to interconnect this earth road with the neutral from the panel (that comes from a grounded wye LV side three-phase transformer)?
It sounds like you're describing a grounding conductor off the equipment shell bonded to the neutral coming in from the utility. This is fine. If you're talking about having two separate ground references on the same equipment, this is not fine.
Had a case where a screw shorted light switch switched line to earth. No RCD. Only symptom was the combi boiler kept tripping out on flame failure. Only when the Utility room light was on (not obvious at the time...) On inspection the live was 140v above ground at the boiler- flame failure detector required more! The earth spike was underneath patio paving, and may have been quite dry... On bright days there was no fault to find!
These videos are great. Very hard to get this information presented in an understandable manner
Just found your channel. Many thanks for these videos. Extremely helpful.
great video, very clearly and well explained. However 2 points. Most of Northern Ireland (rural areas) are still in TT. My house built in 2006 was done in TT. Also when you say neutral is the same potential as earth. Must be remembered that in an AC system half the voltage is carried in the neutral and the lifter you get when you accidentally touch between neutral and earth is worse than live to neutral (or at least always feels much worse!) Overall, well done.
For a commercial building, where the transformer is a private property, will the earth cable from the transformer be connected to the main earthing terminal inside the main distribution board for a tns system? please clarify. Here in pakistan the mdbs are generally earthed by two earth rods...
Muhammad Farooq Fun fact :
In Italy, Spain, Greece, Serbia, Croatia, Albania, Bulgaria and Romania, if you want to make a contract with the pieces of shit known as enel, you would need to buy yourself a transformer and then give it to them for free (as part of the contract you make with them). And most of the time they will be the only option... because they are a regional monopoly... 100% unregulated free market and capitalism go so well together !
Clarity at last! Many thanks.
Great Video John, thanks a lot!, may I ask please - For TNS system, since both Earth and Neutral cables are connected to each other in the transformer side, why does i cannot measure continuity between both cables in my Electrical panel Distribution Board?! This kinda freak me out kindly help! thanks
drich modina There should be continuity between N &E - if not, either the earth is defective, or you are measuring in the wrong place, such as after the main switch when it is off.
***** i measured it in our 63A 3 phase with 1 phase branch distrubution board. I also thought that if i measure continuity between earth and neutral there. Most likely the RCD will trips. Please please teach me where to measure it properly and why does the RCD dont trip if the two cables have continuity. Thanks a lot in advance!
Here in the land of convicts and sea front properties the neutral wire often corrodes off in the outside connection box, we almost exclusively use M.E.N same as your TT supply but each customer has a removable link between the neutral and earth in the consumer unit for testing, this provides a limited path to the transformer when the incomming neutral fails.
There is a label on the cutout here that says "This installation is connected to a PME system" - so that confirms mine. A house we lived in before had a plate on the cutout saying "PME system" too. However, we also lived in one house where the supply came in from the poles, and that was TT. Our ELCB was a Chilton voltage-operated one.
Here in Germany we use TN-Net, TT-Net and IT-Net. The TN is splittet into TN-S, TN-C and TN-S-C. We use normal 3 L Phase, some old houses have only one L Phase. The power cable come in house direct into a big fuse for every phase - at this point the 'Saved Earth' and 'Neutral' go to two difference lines. This place is the exchange point between the power company and my home power net. After this I must install the Watt-Meter from my power company. After this we can install every RCD how we want use ... Most older installation haven't one. For Thailand I not know the situation, we use there an own transformator ...
Is it allowed to make TN-S-C ?
We use TN-CS in the US but we additionally attach a bare wire from a ground rod at the electric meter to the earth terminal in the fuse box. We also run a bare copper from the rod to the nearest hose bibb, I think for discharging lightning. The plumbing would provide a path thru to the utility's piping system which used to be metal. It's probably changed since plastic supply pipes were introduced. Wait, many pipes from the 60's were asbestos-cement which i wouldn't think was conductive so I'm not sure of the system. They may have terminated with a ground rod at the water meter in that case.
im building a steel deck around my pond which will take the mains input while we start constructing our container house. they show the tncs system on the consumer board diagram but in thailand street cables get damaged all the time. im not happy with tncs so im going to ground rod the consumer box, the deck and earth all the 2 wire appliances. the water table is 1m below ground. any input on this would be appreciated.
Thank you very much for a brilliant explanation.
What I'm struggling with at the moment is on TNCS how come the Neutral voltage isn't going straight to Earth at the property? With the E and N joined at the property surely the return would go straight to earth rather than back to the Transformer. It would be like you're sticking the N into the ground. Or have I missed the point?
JW, should I have continuity between my neutral and Earth in a TNCS supply if testing with a standard multimeter from a socket?
Yes, N&E are connected at the point they enter the building. You should also get continuity on TN-S, as although the wires are separate, they are still joined at the transformer.
There is another type of Earthing that you could of included. It is called PNB. Normally used for one domestic supply only to a single phase 11kv - 230 transformer where the earth for the transformer is via the neutral block on a 100 amp cut out connected by a 32mm covered copper wire to earth electrode/pin in the ground. Although historic, lots still exist and are in use in Dorset/Wiltshire/Hampshire and Somerset.
Hi John, If on a TNCS system the Earth at the property is connected to the Neutral, why is there a need for a separate Earth?
Neutrals carry current in normal operation, a separate earth does not. If the earth/neutral were combined in the wiring, any break in the neutral would result in dangerous voltages on any exposed metal equipment.
A combined neutral/earth system is called TN-C, but is not permitted in the UK.
Hi John, Thanks for the clarification......much appreciated!
• TT (Double Terre): 3:07.
• TN-S (Terre Neutral - Separate): 6:22.
• TN-C-S (Terre Neutral - Combined - Separate): 8:24.
• TN-C (Neutral Terre - Combined): not shown.
• IT (Isolated Terre): not shown.
What a cracking vid. Looking forward to watching the rest!
Hi, i have a 1900s house with a lead cable , 3 cutouts (only one in use) and a green earth cable running to a small side box( i think the whole assembly is tar filled)..my house is wired in pvc coated twin and earth...mostly grey, some white...everything works fine. my question is...there is a green earthing wire in the kitchen not attached to anything and one in the bathroom also...should i clamp them to a cold water pipe or just remove them, many thanks colin...
15:30 How did you get the theoretical max loop Z of 1600ohms (1.6Kohms)?
If the trip current is 30mA and assuming 230V, the theoretical max loop impedance by V/Z = 230V/30mA ~ 7.6Kohms = 7600ohms. (Which is of course even more colossal and common sense dictates that's not a good idea in practice!)
+Arglwydd Anfradwrus It's 50 volts / 30mA, as in regulation 411.5.3
If 230V was used, this could result in voltages up to that level appearing on exposed conductive parts before the RCD operated, which would be a serious shock hazard.
Ah, thank you.
I stand corrected. 50V/30mA = ~1600 Ohms, but of course that's still way too high.
I wasn't saying it was right for it to be 7K+, just wondered how you got that figure of 1600 ohms.
Very good explanation.
Thanks for your detailed explanation. Something useful for those of us in Nigeria
JW, in the first section in your drawing you show the earth connected to the neutral on the transformer output coil or winding. But this is AC current. So as soon as the polarity changes (50 cycles per second) the positive 230vac is now connected to the earth creating a short to ground?
No, the only connection to ground is that single wire between ground and one side of the transformer. Whether that side is negative or positive doesn't matter, it's only negative or positive when compared to the other terminal.
Imagine the transformer is a battery. You can connect negative of the battery to ground - nothing happens. If you swap the battery terminals so positive is connected to ground - nothing happens. A short circuit can only occur with a connection between both terminals, or between ground and the terminal not connected to ground.
Hi john I'm currently doing C&G 2365 and have been asked to give drawn examples of Tns, tncs, tt and IT supply and earthing systems. I have no problem with the former three but the IT system is proving problematic to gather info on. Do you know when or where people get trained in this type of install? My 2365 textbook states. IT and TNC systems are not included in this course so there is no information included on these type of installations. Thanks. Phil.
+phil Harvey IT is where the supply is isolated from earth, such as an isolating transformer. Neither side of the supply is connected to earth, or it is connected to earth through a high impedance. It is typically used for medical installations such as operating theatres.
TNC is a system where the neutral and protective conductor (earth) are combined into a single conductor within the installation, so only 2 wires to each item. It is specifically prohibited other than in a few very specific instances, so in reality is never used in the UK. The supply is the same as TNC-S, except that there is no split to separate earth and neutral where the supply enters the building, it continues for the whole installation with the combined neutral and protective conductor.
There is some information on both in BS7671.
+John Ward nice one john. I would guess that training for IT installs is trained by the energy supply company.
I love it. It's like Hugh laurie swallowed the 17th edition. You rock
now it's doctor Ward ;)
One point you didn't mention. If you are far enough away from the transformer, the voltage drop on the lines can be significant. Where I used to live voltage available sometimes dropped below 200v. That meant the Neutral was no longer zero, and could be anything up to 20 volts above earth. Even in my last house there was enough voltage on the Neutral to trip the RCD.
How does neutral gain 20v? (versus dropping)
Hi John,
Great video. Regarding the TT earth, in the event of fault (phase+ground connection) does the current literally “flow” from the consumer rod through the mass of earth and to the transformer rod?
Or is it the case that the amount of current that would flow to earth, would be basis the potential difference between the two rods?
Trying to get my head around current travelling through physical earth?
Obviously this is AC, so the current would be oscillating.
Thanks.
Yes, the current flows through the earth itself from one earth electrode to the other one.
Most of the resistance is at the electrodes themselves, the contact area between the metal and the surrounding soil is the most significant factor.
The resistance of the earth isn't particularly relevant, and doesn't change much with distance. It's a similar situation to an infinite grid of resistors all connected together as described here: www.mathpages.com/home/kmath668/kmath668.htm although in 3 dimensions rather than just two.
Hi John, not sure if I'm missing something. where TT systems are in use, is there a reason the distributor cant fit a TNC-S cable head and make it a TNC-S System instead of using TT systems with high impedances and all of the other problems they bring?
It can be converted in some instances - all depends on how the rest of the network is configured.
@@jwflame cheers for the reply, just wondered as it seemed undesirable to be installing systems with such high Impedance values and having to install RCDs for fault protection etc
we have a Wooden Electricity pole outside our house and down the side of the wooden pole runs a thick black wire (the black seems to be just plastic insulation and where the insulation has brocked away you can see the Thick wire which is silver and not copper coloured), and its tapped to what looks like the Neutral wire on the pole and then the wire just goes either into the ground oif the property, or goes to the meter box on side of wall of property. - This is all put on the electricity supply board not on the consumer side of things. So does this mean the house/premises still has to have one or more earth rods even with this earth wire tapped to neutral line from the wooden pole? - or have the electrical supply board supplied to required earth protection to the house? - the house/property is in the republic of Ireland by the way, just in case the electrical supply is distributed differently to the UK.
As usual always very good and clear. I wish all explanations were this good. Thank you.
😢
If you like this topic , watch a video entitled "EW rice interviews Elihu Thomson " he's the engineer that came up with earthing " and maybe some others around the same time . Go to around 10.27 in the video and he states it was his invention for safety . I like the term you English use "Earthing " ,better than what we in the States use " Grounding " great video ps Mike Holt has good videos on this topic.
Brilliant and very clear instructional video. Thank you John (liked and subscribed.)
In bulgaria we use shuko plugs and we rearly have separate earthing wire.In the wall socket we just put a bridge(copper wire) between earth and neutral and it works nearly all the time.
That arrangement (TN-C) is prohibited in the UK.
Didn't know that.Thanks for answer.
I now want to see an electricity sub station's Earth rod (s). How do they calculate the size / effectiveness?
And how reliable in a real life scenario for the furthest installation in line.😒
Usually lots and lots of 8mmx30mm copper tape buried around the entire sub station it's all designed by the engineers of the sub and presumed loads
Very well explained, one query, for PME System you said that if the neutral (neutral and earth) breaks, it will be dangerous situation because no earth is available. My question is, if a neutral breaks, there will be no supply left because to complete a simple circuit we will need to have a connection of both Live and Neutral. so there will be no current flowing through and have no danger as there would be no supply. can anyone please explain?
In trinidad we merged the TT with TN-CS connection so we put a ground rod in the installation using the TN-CS configuration so is it ok to say we use TTN-CS configuration
Question: you say that the current returns to the transformer? I was under the impression that it just kind of dissipated into the mass of the ground? By what process does it return to the transformer?
Gustav Joncus The ground is conductive, and provides a path for the current just as any other conductor does. The only difference is the ground has a larger impedance than a copper or other metallic conductor.
I understand, thank you
John can you answer a question please? Why when I changed a plug socket front that was cracked, Did I receive a "tingle" from the neutral wire around 30 volts or so, I've had 240 volts a couple of times so I know what that feels like!!! Not that I go out of my way to get it!!! ( Downstairs M.C.B turned OFF for downstairs ring main) But upstairs left on. No I'm not a qualified 'Leccy with 17th Edition but I have worked with an 'Leccy before and I'm very careful about the "quality" of anything I install, hope you can answer thanks Clive
Clive Clarke-Watson Several possible causes such as: neutral can be above earth potential on some TT earthed systems, or TNCS with defective earth, or some incorrect interconnection with another circuit which was still powered.
Thanks John, It is a local authority house built in the early 50s of the Airy type, but has be rewired and has M.C.B board I guess about 25 years ago, It even has all 3 phases into the "board" side (but only one is tapped), Would you as an Electrician be unduly worried if you came across this issue in a house that you were working upon of this age? Just would like to know so I can highlight this to the local authority if you think there is a possible wiring fault. Cheers Clive and keep up the interesting Video's!!
Thanks John. You are a legend!
I always wondered how a path from live to earth was created. I thought it was an enormous earth rod at the power station. Another question, I have a 25m 15a extension cable going over to my shed for charging an electric car. Should I also put an earth rod in the shed and connect it to earth on the extension cable? I was worried the cable might be too long and the car might have a problem with the earth not being good enough. I don't have the car yet.
Shaun Dobbie Very unlikely that an earth rod would be needed.
Electric cars should have a dedicated charging point connected to fixed wiring, as the charger units which plug in to normal outlets will typically take a very long time to charge the car. Extension leads are not designed for permanent installations.
Unfortunately, its my only way to charge. I think it takes 10 amps maximum but the voltage drop of the cable might be too much. It is about 8 to 10v of drop using a 2kw fan heater.
Shaun Dobbie Allowed voltage drop is 5%, or 11.5V on a 230V supply, so within limits with a 2kW load, and right at the limit with a 10A load.
I will just have to give it a try I suppose. The evse with the BMW I3 gives you 3 charge rates. 6 amps is the lowest. If it doesn't work at 10a, I will replace the extension with 6mm twin and earth armoured cable.
The electrical supply is explained wonderfully. My thought is: if we do without grounding, the power supply will be similar to safety Tafo. Wouldn't that be much safer? Unless someone touches the L and N lines directly. Grounding causes more problems is my opinion.🤔
It's safer but only until some fault to Earth occurs somewhere - it's then an uncontrolled earth referenced system.
Isolated supplies have their uses, but only in strictly controlled and monitored environments.
@@jwflame You are extremely competent and know what you are talking about. What has become so rare today. Thanks!
Hi John - Great videos, very informative - On this subject, on my house I seem to have a mixture of TN-S and TN-C-S. It looks to me as though the DNO have installed two cables in the TN-CS arrangement, and then AN OTHER has popped in an earthing rod for good measure (on a piddly little cable I may add). Would this be problematic at all do you think?
GREAT VIDEO....Hi john, recently visited a rural property TT supplied overhead 2 wire supply. where an electrician had found a voltage 54 v between earth and neutral. When installing a shower circuit. But could not find cause of the problem. Pulled the cu to bits and was left stumped. I myself called and isolated the installation and conducted tests at the distributor s supply only. I found a voltage of 280v to the property's electrode, which my meter could not perform a EFLI test on. Also I found a voltage of 54 volts between n+e. I put this down to distributors issue, as a visual inspection in the cables showed cables running some distance and twisted together for a section on the way back to the transformer. Opinion please john thank you
@jwflame With a broken PEN in the TNC-S arrangement, can't the contact voltage be minimised between exposed conductive parts and the general mass, by adding an earth electrode which will connected to the consumer's MET?
Yes it can. However to have any meaningful effect, the resistance of the electrode would have to be very low, typically under 10 ohms.
Hi, on a tt system what is to stop someone simply linking their main earth to the neutral instead of installing a rod and putting up with high earth loop impedance? Just curious
Thanks
This is what we have in Greece as well and I am under the impression that by law all buildings should also have a grounding rod that connects to the provider grounding cable.
Hi John Ward,nice video. I would like to know if you could perhaps explain how one would go about choosing which type of supply to use. If you designed an installation from the ground up.
There isn't really any choice - you get what is provided by the electricity suppler, which is usually TN-C-S on newer installations and TN-S on older ones.
The only choice is to not use the supplied earth and make it TT - but that is significantly inferior for most applications, so unless it's a specific situation where TT is required, you just use whatever is provided.
John Ward thanks John and what type of applications would one expect to use a TT type system. I know IT systems used in medical locations for reasons i think of no earth fault tripping the supply to the entire installation.but TT im still unsure of where one would prefer that system.
Hi John,
I stopped the video at 2:45 'cause I was shouting at you! The mains transformer secondary winding can't be 230v one side and zero at the other since each side oscillates between 0 and 230v 50 times per second. Shorting one side to earth would strap both secondary winding terminals to zero, just before the input fuse blows... :-(
Tim.
Err, no. The neutral always remains at earth potential and the relative line potential alternates about it.
Err, no. The neutral always remains at earth potential and the relative line potential alternates about it.
JW, could you expand further as to the earthing of a portable generator please? I use a 1kw Honda invertor generator on board our boat, generally for battery charging only. It represents a particular problem as afloat there is no possibility of an earth connection. The boat has a 240v shore power circuit on board which is generally connected to the mains supply in the marina when in the home berth. But when away cruising I plug the generator in to the shorepower inlet socket. Other boat users have suggested that the generator to boat shorepower connection cable should connect neutral to earth, infntbkniw what the thinking is behind this suggestion.
Your videos are very useful indeed - keep them coming.
Many thanks,
Rob