Understanding Earthing Arrangements - TNCS, TT, TNS
2024 ж. 2 Мам.
45 024 Рет қаралды
Understanding the earthing system used in electrical installations is essential. Joe Hammond's video provides a detailed explanation of the different earthing arrangements commonly used in UK electricity supply systems. TNCS, TT, TNS
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00:00 Earthing Arrangements
01:00 What types of earthing systems are used?
01:26 TNCS
02:30 TNS
02:50 Top tip from Joe!
03:30 TT
04:10 Challenges of TT Systems
04:40 Earth fault loop impedance - Appendix 4
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Joe, this is a really fantastic video, simple, intelligent and well presented. It also has a huge impact on the type of SPD that is installed so I have shared this with our own apprentice to help him understand. Thank you so much.
I really love the explanations you gave in the video, I would love to undergo apprenticeship in your noble company. I am Inkoom from Ghana - West African.
an American electrician here, it is so different from what we do in the US we usually Bond the equipment ground in the neutral at first means disconnect and then ground rod placed
Yeah. Very similar to the TT arrangement but the earth and neutral bonded at the main panel.
@@TheDrew2022 yeah the TT is pretty similar we have in the US there are some differences.
@@jackl7731 No, TT is completely different. In TT there is no connection between earth and neutral. RCDs are mandatory in it on every circuit. There often is two levels of RCDs 100 mA and 30 mA. TT is banned in the US. The US system is TN-C-S. Typically one has a ground rod on TN-C-S, in Finland for example one has a 40 m horizontal rod if one has not put it in the foundation of the building. UK is exception that no ground rod is required.
In Australia, pretty much all LV installations are TN-C-S AND with a local earth rod connected to the local earth AND the incoming neutral, locally referred to as multiple earthed neutral (MEN, voiced as ‘em-ee-en’). In some areas, the high voltage ‘neutral’ is common with the LV neutral, so common MEN (CMEN).
Not sure how things go in your part of Aus but there isn't usually a HV neutral per se. It's an isolated delta supply. The C-MEN (ok rest of the world, stop sniggering, I can hear you) refers to the earthing of the transformer tank, and any other metalwork that could become energised should a HV fault occur, in relation to the LV neutral earthing arrangements. There's a fair bit of documentation from Ergon/Energex in QLD regarding C-MEN if you do a web search for it.
Linking the earths and the neutrals inside the distribution board is a bad idea though because it increases the number of places where an open neutral can happen and make any earthed conductive materials become energized (which is the most dangerous electrical fault because breakers are rendered useless during this fault). The neutral and earth should split at the first point of disconnect like in the US or UK, not in a distribution board like in Aus or NZ. Thus if an open neutral is to happen at the first point of disconnect or anywhere at the property, your earths are still independently linked to the PEN (combined earth neutral) conductor supplied by the network.
@@IAmThe_RA Actually you might want to look into what you've said here a bit more deeply. In the USA, as in AU/NZ (and others for that matter), it is permissible to start a new MEN (AU/NZ) or MGN (USA) earthing system in an outbuilding providing that outbuilding is electrically isolated. Only phases and neutral are carried to the outbuilding in this case, a new neutral/earth link (bond) is established along with local earth electrode and bonding as required. This aside both MEN and MGN will typically have a N/E link in the main switchboard/panel with subs within a single structure not having such a link for obvious reasons. Refer to NEC article 250.32.
Great video Very well explained
thanks for your insight
Here in Australia we have the ground stake at your house, a water bond and an earth-neutral bond at your home fuse board
Hi, I have a TT system in my house. I'm putting a 10 sq swa cable to a shed and fitting a separate earth rod at that end for fuse board. How can I protect this cable against fault damage in the ground as the earthwill not be connected off swa at shed. 😊
When you have a earth rod, next to the home, and supply power to sheaf, workshop, outbuilding etc is it good practice (and allowed) to add earth rods at each remote building?
Yes, you can wire outside buildings as TT wiring just the neutral and line/live and then providing a protective earth via the grounding rod. Indeed, as you have to bond any exposed metalwork, such as water pipes, using some fairly chunky cable back to the consumer unit, on TNC-S systems, it's often easier to have outbuildings and garages as TT systems and then you only have to bond to the protective earth there.
Earthing Arrangements for mobile or transportable units with or with out the uses of a earth electrode?
In Germany, TN-C-S has earthing in every house. Where the lines enters the house.
Hi Joe, my background is is in maritime engineering where generally we don't have earthing systems but have earth fault detection instead. Anyway my question - we have a TNCS installation and have had a home battery installed. In the event of a grid power supply failure the house is disconnected from the grid (including earth loop) and the battery continues to supply two circuits. The battery has a earth spike connection so I guess that in the event of a power failure we switch from being a TNCS system to a TT system. How can I find out if the earth spike (one meter) has a sufficiently low resistance to activate the safety devices. The house is built on sand and I am concerned that in dry conditions the resistance to true earth will be high.
In my country TNC was often used some years ago apparently. Which is just Line , earth and neutral combined. Often you would connect the earth notmaly and then take a cable from there to neutral connection (on outlets for example.
Great advise as always thank you 👍. You sound like presenter from Jackanory 😂 😂 😂
On a TT system, what if you install an earth stake directly connected to the N coming from the supply. And have a separate earth stake for ground within the premises ? Wont that be better for the RCD trip times ? (Assume the supply transformer is far away from the premises)
I do not know what you think you try toi achieve with the local grounding of the neutral.
How about IT (Isolated Terra) systems, which I believe are or were common in places like hospitals?
Specialist stuff IT systems - hospitals, chemical plants and some residential in Norway!
IT systems are also common in larger PV installations, mostly due to anti PID implementations of certain inverter manufacturers (talking about >10MVA plants)
Operating rooms use IT as it works despite a failure. One cannot have the power cut in an operating system.
Awesome content, regular watcher & subscriber for years. Have you considered doing a video on DC SPD’s ? The regs (or lack thereof) surrounding them & practical applications.
It’s a good question and we are seeing them on the DC side of solar.
What is the cable requriement for Earth for TT system as Ze will be high due to soil
In our swamp called 'the Netherlands' TT works best. Only on some sand grounds here during hot summers some older sub-standard groundrods fail their resistance.
what book are you reading sir
A portable power bank with 230 volts is an IT system. No conductor is connected to Earth, so there is no neutral. There are only two lines with 230 volts. This is safe for one single device. But it is possible to make a TN-S system out of it, earthing !
Actually not as there is no earthing. Many try to mistakenly read the codes as a sentence: TN-C-S. Earth and neutral first combined, then separate. That is not how they work. The letters have specific meanings. The first letter defined what is done to the neutral point of the transformer (Isolated or Grounded). The second defines what is done to the CPC (Grounded or connected to the neutral point of the transformer). The third specific if the connection is combined or separate. In IT one does not typically distribute the neutral as then grounding of a accidental phase would give 400 V to other phases. If one keeps the line voltage at 230 V and does not give the neutral the voltage will be only 230 V.
Single entendres a speciality. 😀
How can a transformer be on a telegraph pole? Surely you mean an Electricity pole?
So what if that pole carrying both, electricity and Telecommunications cables, what do you call it then? A telegraph and electricity pole? What if the pole is carrying optical fibre internet communications cable too? What do you call it then? A telegraphic electricity and data comms pole?
@@deang5622 You are clearly not an electrician or telecomms technician. Power lines never run on telephone poles. Sometimes phone and cable TV may use electricity poles.
@@greenpedal370Actually I am a degree qualified electrical engineer that has worked in Comms for years. I'm taking the Mickey out of your post. So next time don't assume the other guy isn't qualified because they might be very well qualified. And you can run power lines, telephone lines at the same time, it's not ideal but they do actually do it in the USA. Perhaps you have never heard of balanced line transmission. . And data lines? You can run optical fibre along the same poles as high voltage lines. The optical laser light is not interfered by the high electric or magnetic field strength caused by the power lines. In fact in the UK a power company has run optical fibre along its high voltage transmission network pylons. So put that in your pipe and smoke it. See, I am not as dumb as you look. You can apologise to me later, if you have got the balls.
@@deang5622 Me thinks thou dost protest too much. You are just waffling.
@@deang5622 You call yourself and engineer yet you do not know the difference between an engineer and a technician. TROLL!!!
4:25 funny.. all consumer house here in Belgium are TT .. with eart rod or earthing loop in foundations ( resistance has to below 30 ohm ). Never get a PE from the grid. TN-C i see a lot in factorys 3 lives and 1 PEN conductor ( with thier own high volage transormer cabine ) then we a lot convert them to TN-C-S .. PEN -> PE & Neutral .. if we need 230V .
In Finland most homes up to the late 80s used TN-C i.e. no separate earth wire. After that the norm has been TN-C-S. TT is very rarely used. The TN-C causes problems as it is not compatible with RCD unless one installs them in the sockets.
TT is the system in Italy too, but RCSs are mandatory.
@@giacintoboccia9386 RCS = RCD ? .. here we have to have everything after a 300mA main RCD .. and as of june 2023 new regulations .. all light & sockets have to be on a 30mA RCD with a max of 8 circuits .. so every 8 circuits 30mA RCD requirerd BEHIND the main 300mA RCD .
SparkyNinja and co did some really good vids on earthing and bonding. Parts 1 and 2 were each over an hour long, and got watched from start to finish. So, you know, don't feel you have to keep these vids to 6 minutes or that. More please 🙂 Also, were the colours the right way round on that diagram of the transformer?
while good for explaining, i believe the part of the "ground fault making a loop back to the line and going into the protective device" part to be inaccurate. firstly RCD devices operate on the imbalance of the two incoming wires, if your fault sinks current to ground, it doesn't "come back" trough the neutral, thus trips. i really don't know what you're on about with it "going back up into the line", you draw current from the line and sink it to ground, that's what trips a fuse or protective device. any voltages on the neutral line will sink directly into the ground stake at the transformer, not go back up. in that regard TT and TNS/TN-C-S systems perform nearly the same, there isn't any "delay" as it sinks to ground either way, the only benefit i can see is that having a main grounding spike means it's probably much better looked after
No, wrong. The current doesn't sink to ground. That is incomplete. For current to flow there has to be a circuit, a loop starting at the voltage source, through any loads and wires and then back to the voltage source from where it originated. That is basic circuit theory. No complete unbroken loop, no electricity flow. When a fault occurs and electricity travels down through the earth wire, there has to be a path back to the voltage source from where that electricity originated. That loop may involve going physically down into the ground but it has to get back to the secondary winding of the distribution transformer in the street, and depending on the earthing configuration in place, one way that is done is using the PEN conductor from the distribution transformer to the property, which can be considered to be "a line".
@@deang5622 The current does not go back through the earth. That is just a model we use as it works. In reality 230 V goes just a meter or two. If it went back through the earth the earth resistance would mainly depend on the distance to the transformer and not on the local soil at the earth rod.
If electricity can flow through mass of earth a long way , how would we not feel it and receive a shock from the ground if this happened?
Because it has what is known as a potential gradient. Where it enters the physical ground it might be at 230 volts. 5 metres away it isn't 230. It's lower. The ground has resistance and that resistance increases as the length of ground the current is passing through increases. Think of a potentiometer here with a carbon track and a wiper. As you traverse the length of the path of the current in the ground, the resistance will increase and the voltage across it will change. If you are too far away from where that voltage and current enters the ground, then voltage potential you are at is too low for you to experience a shock, despite the fact current is travelling through the physical ground.
If you run 230 V to the ground and step next to the rod with the other leg a meter apart you will get a nasty shock that will go through the vital organ. Current will go a few meters to the earth and that's it.
@@okaro6595 Almost right. Current will go through the ground, the resistance of the length of the path through the ground affects the magnitude of the current. The current will go two metres, it will go 100 metres, it just a question of what the magnitude the current is. But it's wrong to think of this matter being the current. It's actually primarily to do with the electric field strength which is expressed in volts per metre. As you move away from the point where the current enters the physical ground, the electrical potential reduces. But at any given distance from that entry point, the voltage is non zero. The higher the voltage at the point where the current enters the physical ground, the greater the electric field strength and for a given distance from that point, the electrical potential is greater. Other factors come into play such as how many legs you have. No I am not joking. Four legged creatures such as cows, cats and dogs are are greater risk of electrocution than humans. And in farm yard situations where sometimes the power to the farm is medium or high voltage and conveyed using overhead bare cables, there's a bigger risk. Electrocution is less likely to occur for humans if the only contact with the electricity is through the feet. This is because the current passes up one leg and down the other. In the case of our four legged friends, the current travels up one leg (or even more) and has the opportunity to travel down the length of the animal's body and across the heart, and out through another leg back to the ground. It's that current across the heart which then interferes with the electrical signals of the heart which are required to make it beat. Even the physical separation of the legs of the animal, expressed in metres, has an effect. Legs too far apart means the potential difference across them is greater and can be enough to develop a high enough current to cause ventricular fibrillation. So you will find that bigger animals such as cows are more at risk than a smaller animal because their legs are further apart.
Can we change TT system to TN-S?
Think about it for a moment. Where would you get the separate earth contact?
I have a couple of questions... What you mean (4min05s) that current "takes some time" through the earth 🤔? No no. And why do you say TT systems are becoming less common.. are you sure? Not in Europe. It is a long engineering discussion if TT systems are cheaper, and more secure than any other schema, but let me just say that it is (at least) daredevil to say the opposite. In any case thank you and good video.
A few mistakes in that video…….poor editing. But over all, not a bad try 👍
As a Yank, I’m more “grounded” than you Brits!
Nice pun. It's literally true. The UK's take on TN-C-S did not require a local electrode while over there with your MGN system you have a mandatory electrode, the local N/E connection as well as a N/E connection between the HV (primary side) and LV (secondary side) neutrals and the supply transformers and periodically along the poles to contain neutral voltage rise (relative to the physical earth) originating on the HV side. Important to remember that while TN-C-S is used in the UK, USA, AU/NZ and others the local implementation is different so re-using terms (PME) from one country in another is a bad idea as it leads to confusion.
As not a Yank I am more grounded than you all
@@retrozmachine1189 you gathered my meaning!! It was meant tongue-in-cheek-superficially. But you addressed my deeper meaning in your post. We do need universal protocols in the industry.
As a "Yank" your average Mass is usually greater than everyone else's... so yes, you've more chance then of being more grounded. 🤣🤣🤣
@@Sparks1Plumbers0Are you suggesting that Yanks their their weight around? 😎
well the value are not the same so you have to make sure you in the acceptable ZE value for reference here is the MAX allow values TNS 0.8. (Terre neural) separate) TNCS 0.35. (terre neural combined separate) TT 200 (terre terre) by the way second year of existence and you don't know how earth is so important pls go back to college you may save you life and other ppl life
What's happened to this week's eFIXX News? 🤔
It's been grounded, apparently.
Joe has just returned from holiday. news will be released later today.
😂
Where’s the real Joe?
Australia and NZ are exclusively TT and there's bugger all consideration for where the rod goes. You'd want to be as close to the transformer and as far away from other properties on different phases - alas, no such skill.
Totally incorrect. Australia and NZ are almost exclusively TN-C-S with a smattering of TN-S and TT and IT, all three being comparatively specialist supply.
@@retrozmachine1189 Earthing system is dictated by the distribution type. Providing L+N and bonding in the board doesn't make TN-C-S. It makes an MEN system. TN-C-S have PE and N bonded at the service head before it enters the DB. It's a TT system with extra steps.
@@grahamek86 Do us a favour, would you? Write to the IEC and let them know they have incorrectly classified M.E.N. and while you are at it let them know they have incorrectly classified the USA's M.G.N. system too.
@@retrozmachine1189go on my man 😅👌
@@grahamek86 "Providing L+N and bonding in the board doesn't make TN-C-S." Oh yes it does. If at any point (and it doesn't matter if it's at the service head or inside the a consumers distribution board) the neutral is interconnected with the ground/earth then it is, by definition, a TN-C-S system. The supplier is still providing a metallic return path for fault currents to earth/ground then it's TN-C-S. The "C" part stands for "combined" and the "S" for separated. The exact physical point of the separation is immaterial. The issue of multiple earthing points on the combined neutral/earth conductor is another matter. All good TN-C-S distribution systems will have that, but it's not what defines it.
Grounding
Grounding means connecting the neutral to the ground. Earthing is about the earth wire or the CPC.
Obviously American...😉
@@okaro6595 Actually there are two earthings in our electrical installations: An operational earthing (called the neutral or simply N) usually the insulation is of blue colour and the protective earthing called "circuit protective conductor" (CPC) or "PE". The last one is green/yellow. And you got a combination of both, the PEN of the TN-C-S system is green/yellow and supposed to be marked blue at visible ends. Sometimes on conversions from TT to TN-C-S it can also be blue with green/yellow on the visible ends. At least here in Germany. And of course one thing, that is usually not worth mentioning in the UK since the final circuits are always TN-S but here in Germany TN-C was permitted in final circuits until 1973: Once the PE and N are separated you are not permitted to rejoin them again within the installation.
Good to see you back in the comments Marcel