Earth Terminal Voltage Drop TN-C-S
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- Опубликовано: 5 июн 2024
- How the earth terminal on a TN-C-S supply can be at a different voltage to the true Earth.
As the neutral and earth conductor are combined outside the installation, current in the neutral causes a voltage drop, which results in the earth terminal having a different potential (voltage) to the true Earth outside.
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JW's choice of words always makes me smile - "not entirely implausible" - this is the kind of guy you need involved at design time on anything mechanical or electrical AND at the quality assurance phase. Phenomenal attention to detail with just enough allowance for practicality. Design engineers hate this kind of guy being introduced to the process as it means they have to actually... um... design something safe rather than copying a template. Imagine... actually having to do your job to earn a living... the horror!
A very clear and concise explanation John. Great video as always. The supply network will always limit the VD. I remember on houses with suspected issues my old mentor would leave a 6V torch bulb in circuit N-E. When he came back if it was blew then he knew lol.
Local generation and battery storage perhaps a solution to issues in the supply network. Cut them out the chain!
For some reason this brought to mind Open University programmes shown late at night on BBC2 many years ago. I was young then but I presume they were designed to be recorded to VCR for playback later - they just broadcast them in the early hours as the regular live view broadcasts had ended, the transmitters were up and running and it was preferable to expending all that energy to broadcast a test card.
Like in Hungary, we must instal earth electrode by every single house/meter. To keep the local ground and actual PE wire on the same potential.
Same in Finland.
Same in Germany.
Most countries have been doing that for ever.
In the UK, it's been permitted for ever, but is never done because it's not a requirement.
Same here in Australia, we simply call it MEN. The earth connection must be to a stake and if possible to a water pipe.
The only hazard our system can develop is from a faulty neutral connection on the supply side. Then the neutral current flows through the earth and a potential difference between grounds can occur. Thankfully most of us take even tingles in the shower or hot tub seriously and call someone competent pronto. I'd also add that all new installs or upgrades mandate RCD protection per every circuit. As a result pretty well any errant current is going to trip an RCD which can lead to problems with nuisance tripping but sure less of a nuisance than a funeral.
Exactly the same in Australia, only power lines come from the transformer on the pole in the street.
When I was a resident engineer in a Derby Factory we ran the radio off the 9v Natural and Earth through a rectified power supply. Bit norty but free power !!!.
U would have thought being an engineer u could spell naughty
Wow these videos have opened my eyes. I always assumed T-N-C-S was superior as it was most contemporary and common. Interesting stuff.
Contemporary isn’t always superior 9/10 it means cheaper and economical for the supplier
These recent videos are greatly appreciated. I wonder when the decision was made to make TN-C-S the standard earthing arrangement. Was it after the network was privatised? It's also interesting that the seemingly superior TN-S was the default system when the first electrical services to homes were originally laid in the ground, and now it's all been vandalised.
TN-C-S has been commonly used since the 1970s, possibly earlier in some areas, long before privatisation was even considered.
@@jwflame Yes here it has been around a long time, when the supply was overhead bare copper 4 conductor cabling. You can save a massive cost in doing a distribution network in only needing 4 current carrying conductors, and then having a grounding rod by each consumer metering point, as you cut around 20% of the cost of the cabling and pole loading. Even after the copper cables were swapped out to ABC they stayed with 4 cores, as this made retrofitting much easier.
You can tell though just how long a property had a single owner though, as you still get properties that use 3 copper wire bare feeders to them, only ones in a street, so they have not changed owner since the 1980's when they would make replacing the cable a prerequisite to get the property transferred, though often the change was simply to swap out the old 3 bare wires to a split concentric cable running from the original pole attach point to the original roof attach point, and then reuse the old DCC wire to the meter from there. The newer versions of that use aluminium cable from the pole to property, lower cost to the metro, as they keep the cable and connections in stock in bulk for distribution upgrades and repairs.
Now if only they would replace the shorting blocks on street lamps with photocells when doing the rewires, instead of either just leaving them disconnected, and no longer on group control, or wiring then to a phase and leaving them as dayburners.
Great stuff, really nice video.
Food for thought and perfect timing what with garden lighting/ hot tub installations being asked for at this time of year.
Very hard to explain to a customer that an earth rod/ TT system must be installed because of voltage rise on the earth which is in fact the neutral and vice versa
and it's going to cost more money to install your hot tub and patio/ garden lights safely especially if you want shiny metal garden lights that have to be connected to the CPC.
Plus there's also the risk of damaging something by driving down 2 or maybe 3 metres of copper rod to get nice low Ra readings and also the added cost of a time delayed RCD to protect the supply cable from the house to sub board prior to TT separation.
Oh Yes It's very hard to explain all this indeed.
Why not just buy a double insulated hot tub? Preferably plastic
Grounding or earthing is one of the more difficult concepts for people to grasp. I learned from experience.
Good video for Awareness.
Thanks J W
Thanks for a great video, very clear explanation.👍🏼
I see stick man is excited about the hot tub.
Phew ! it started with an S not a D ...
As an electrician state side it is interesting to see what the difference are between your codes and ours for the services and grounding (earthing). Here we don't do TT in residential or commercial, it is all CN-T-S. In a home with metal water service the primary earth IS the water pipe. We also drive a supplementary ground rod that is 5/8" (1.6cm dia) and 8ft (2.4m) long in the ground. If the service is larger, 200Amps, we will add a second ground rod a minimum of 6ft (2m) from the other ground rod. Ground rods are tied to the first means of disconnect with 6ga (13.3mm²) bare copper wire. If there are a pair then that wire is a loop of 6ga starting at the panel then the first and then second rods and returning to the panel. Water bond for a 100Amp service is 6ga and for 200Amp services 4ga (21.2mm²). Our only neutral to earth occurs at the first means of disconnect. That is generally the main panel. All delivered services here have grounds at each pole tied to the neutral. This neutral is also combined and servics as the neutral for the primary on our delivered services in residential above ground. Poles and transformers. If everyone keeps their grounding and bonding in good condition then loosing a neutral, though not good, is not a catastrophic occurrence. If your ground bond is compromised then you can end up with allot of magic smoke being let out of electrical equipment in the home. This is an issue you don't have there and is particular to our 120/240 split phase home service. The same applies for out 120/208 and 277/480 3 phase systems as well. Interesting video .
The tongue test was the only way to check a 9v battery when I was a kid; if the transistor wasn't working that was the first test - you could tell by how much 'zing' it gave you if it was good or not.
Hello. In Romania we have a TN-C-S system and each house must have a local grounding of at least 4 ohms to be connected to the PEN. We call it neutral treatment.
Below 4 Ohms,not at least 4 Ohms.But most houses just have the PEN seperated into PE and N without a ground electrode connected.Many poles dont have ground electrodes either,so the nearest ground might be 100 meters away from your house.
4 ohms for the earth rod? How do you get such a low value? Special treatment to the soil? Extra long earth rod?
@@nahuelparabere5569 Many countries use a steel plate in a trench around the house. It should be more than 80 cm deep.
Interesting timing... Rodalco2007 just uploaded a video explaining SWER (single wire earth return) isolation transformers used for HV electrical distribution in NZ. Point of grounding in the HV distribution system (and isolated with no grounding) can affect the
I love how confidently you said "if you don't think 9v is a lot get a battery and lick it" 🤣🤣🤣🤣
Brilliant videos ...well done ✔👍
Nice video!
One remark: at 1:34 E is connected to different earth closer to object, not at the same E of a transformer.
Thanks for sharing!
Thanks for the great videos John. Considering hot tubs and swimming pools, why don't we use isolation transformers with protection and double insulated secondary circuits. That's what is done on site with 110 V power tools?
They could be used, but the cost is why they are not. A transformer for that would have to be continuous-rated, making it a very large and expensive item. Such transformers do exist, mainly for marine ship to shore and other specialist applications, in terms of cost a 32A type is around £700 - not exactly an attractive addition to the costs of installing a hot tub.
Thanks John
Hello john. I like the blue coloured lights in your Studio. Or workshop.
Excellent presentation. One question, how realistic is a 0 ohm earth resistence from the TX to consumer, (equipotential earth) like is implied in this scenario? Thank you.
Best voice ever
Maybe there are subtle differences in the standards used in different countries or so, but here in germany tn-c-s requires you to connect to a real earth at the point where you split it and I see it all around here being done, also in all documentations about what tn-c-s is there is that additional earth, also I doubt that rcd requirements could be fullfilled without it
With so many issues surrounding TN-C-S do you think the UK will ever go back to using TN-S with more modern type cable? (3 core SWA or Split Concentric)
I know it's about making it as cheap as possible but when it becomes dangerous and/or deadly surely things will have to change.
With more EV chargers being pushed in TN-C-S just seems like asking for trouble.
Companies are getting better at making EV charging points with built-in PEN detecting fault technology now.
In Ireland we only have tn-c-s but have to put in an electrode to supplement on every job, I always wondered if the body of an electric car is earthed?
When is Earth is not Earth?
Me: When you are on Mars like I am.
JW : T-N-C-S
me : oh... I was close though
So, if we ever get around to colonizin' there, will we ground power or "mars" it?
@@Madness832 Earthed 😂😂😂
@@Madness832 Mars has ground just as Earth does. I suspect you meant to ask "Will we earth power on Mars or Mars it?"
@@robroysyd That's what I asked. Would it still make sense to call it "Earth" if not on said planet?
I jus come across this video and its another very interesting informative...but i notice in your calculation that u had (0.1 ohms) from the nearest point from the transformer and its the same (0.1 ohms) at the furthest point....jus wondering
John, have you got an explanation of why an RCD test button does not work when there is an E-N fault on a TNC-S system.
and how an RCD test button works when pressed.
Hope you can help .
Quick question how do you determine or work out the size of the cut fuse. Ie 100amps or 80Amps Is by the Ze or PFC
Hope your can help.
The only way is to remove the fuse and look at it, or ask the DNO to do the same.
Great video 👍 if it was tncs with a hot tub and volt drop of 9v, could you put a earth rod in just for that circuit??
Perhaps - see the previous video for the problems in doing that.
ruclips.net/video/S5OtLg6voZY/видео.html
Hi John forgive me I've been drinking, but it occurs it might be better to run this shebang via heat exchanger coils from the water heating system
Hello John, I’ve bit concerns about this, I might be wrong. I was thinking that we’ve step down transformer which converts voltage down and current up so it pushes 253v-230v to last connection of installation in parallel so that we could have same voltage as much as possible and we distribute current throughout the consumer installation according to our amps capacity of source. But yeah we still have resistance which will result voltage drop but my concern is that I thought voltage drop is lost energy as heat so if that voltage is already lost how it can cause effect on something? I was thinking that it only can give electric shock if it hasn’t sufficient earth connection to the source of energy. Except some other problems to consumers or installations... thank you!
Hi John, when the installation is using a TN-C-S earthing arrangement and they incorporate PME. Does this mean that each additional earth electrode is a parallel path back to the transformer through the physical ground itself? As a result of this there will be current flowing through each earth electrode back to the transformer as there is a slight potential difference between each of the ground rods back to the transformer? Many thanks in advance.
Yes. In a PME system current flows via anything connected to Earth and the combined N&E conductor, and that includes bonding to metal water and gas pipes, earth electrodes, steel buildings and so on. The resulting magnetic fields can cause problems with equipment.
@@jwflame Many thanks for the response John it is always appreciated. Just to clarify that this is in normal circumstances that current flows via anything connected to earth and the combined N&E and these are all parallel circuits? In a different post I was told that "earth and neutral circuits are only allowed to be bonded at a single point, otherwise the earth wire would have varying potential along its length since it would be a parallel circuit". Am I correct in understanding that this statement is only true for anything after where the neutral and earth are combined in terms of the consumer end to stop current flowing through the earth wire. But anything before the neutral and earth link can be bonded as much as you like with earth electrodes or metal water and gas pipes which ultimately are all parallel path back to the transformer as the neutral is earthed back at the transformer end? Hope this makes sense John and I look forward to your response.🙂
My mate’s Earth was 1600 ohms. I advised him to get it sorted before his wife or kids got electrocuted, he didn’t bother, reckoned the RCD would catch it.
Mmm. This could explain why I could feel a buzz on my arm when leaning against my caravan last year ( like when you lightly touch a touch-switch table lamp) it wasn't unpleasant but definitely unnerving. I'm guessing the earth on the electric hook up was a few volts more than the grass below, as there was no stake at the hook up socket...
Caravans are not permitted to be connected to a TN-C-S supply.
@@jwflame correct John, and being a large site I'd assume it was correctly installed and certified. But I can't think of any other explanation, and the neighbouring caravan occupant said his felt the same
I was at a job where I had to check out a pontoon that was supplied power from the house main switchboard. I did a few tests and discovered that the pontoon aluminium had 2volts on it. Then I discovered that it was earthed from the protective earthing conductor from the circuit supplying the jetty and that the neutral back at the main switchboard had 2 volts on it as well (The earth's and main neutral are connected together at the main switchboard) I was curious about how significant 2 volts was especially in a wet area so I wet my arms and the aluminium deck on the pontoon and put my hand in the water and I found out straight away about my previous unknown little cuts on my hand 😆
The perils of single phase distribution of TN-C system.
I would though expect the distribution company to have a 3 phase in the street cable, and thus with your example 0V drop in the line from transformer to the first house, then only 3V between the first and second houses with then additional 3V to the last house.
3 phase cables are often used in the street, but that cable can supply 20, 50 or even more properties. It's very unlikely that the loads will be balanced across the phases, so there will always be some current in the neutral.
That is correct, but the more properties you have on the 3 phase line the more they will balance out. It will though require great deal of luck to have it Zero current in the neutral.
It will be lot less than the 9V drop in your example. TN-S is the way to go.
If the water pipes in the house are bonded to earth doesn't the cold water feed link all three houses earths together? What sort of impedance does that give and does the current flow to actual ground cause electrolytic corrosion of the pipes?
Like mentioned in previous video, wouldn't groundingrod from TN-C-S junction to ground solve this issue (evening the potential difference)? In Finland this is mandatory to do anyways while TN-C-S is also used virtually everywhere. To be more precise, I think loop around building or generally long enough metal is needed also, not just "stick in the ground in corner of house", for making sure bonding is adequately made.
Yes it would.
Unfortunately in the UK, that is optional and therefore never done.
Keep it going john, more to come...
TN-C-S... the biggest mistake the UK electrical industry made in the 1970s... and who pays... we all do🤦🏻♂️
If done correctly, TN-C-S has great advantages over other systems. Local proper grounding is the key.
@@Poebbelmann Any system relying on being done correctly is asking for grief. Especially given the laughable state of some of the Part P types making a joke out of the electrical industry these days.
@Sebi Local grounding for TN-C-S isn't done in the UK.
It's not entirely one sided, at least in the event of a break in the earth, you have a bunch of irate customers phoning up the dno to find out why none of their stuff is working anymore, a TNS would just fail silently, leaving no clue it had done so till someone had need of earthing.
Admittedly it would be more dangerous in the mean time, though Bonding would take the edge off.
Take your pick: dangerous for a long time, or even more dangerous but for a comparitively shorter time.
Thank god that type of fault is relatively rare.
I've got a 9.2kW water heater in the kitchen. It's wired up to the cooker outlet. The outlet goes back to the consumer unit using 6mm² twin and earth which seems to be rated up to 45A. The breaker on this circuit is only 32A. It all works fine as I understand it takes a while for overcurrent on a breaker to actually trip it and the heater is only used in short bursts. I can't see any reason why this setup would be potentially dangerous as the breaker is lower than the current rating of the heater and the cable is higher, so the worst that can happen is the breaker trip out if the heater is used for too long right?
Rather than guessing wether it is ok or not, get an electrician out to look at the installation and have it inspected. (When in doubt call a professional)
@@realtoolsrealreviews5173 Have you tried to get a sparky out these days? Every single one I've called has said they'd ring back and NONE have. Why do you think I asked the question in the first place? And guessing? It's not a guess, it's a hypothesis which I'm asking is correct or not. Eventually, I'll probably manage to get a guy out, but until then I'd like to confirm if every time I turn the hot tap on I'm OK or if I'm gonna burn the house down. Currently, I'm hardly ever using the hot tap because of this. So instead of the passive-aggressive non-reply, how about you actually try to help. And if you can't, keep your comments to yourself.
@@nicholasmarty4370 You’ve totally misunderstood the point of my comment, first and foremost i always say to everyone to get a professional out to check things if in doubt about something (as you’ll get the right info first time and it done safely) due to my time spent working in a diy retailer and the questions we get asked about electrics from the general public is unbelievable and dangerous as usually people have no idea what they’re doing or just enough to be dangerous. Since you have now pointed out that no electrician at the moment can look at the installation and you have even tried ringing to ask the question and have had no luck i will offer my opinion (I’m not a qualified electrician but i have understanding of the simpler mechanics behind it so don’t quote me on this). Ill break this down into 3 parts
first the hot water heater (I’m going take it as its an on demand instant water heater) at 9.2kw at 240v uk mains voltage is 38.33 amps drawn
secondly the 6mm cable feeding the appliance which after checking a well known cable suppliers website lists the current rating at 40a so assuming that the cable is the correct mm2 for the length of the run (sized to reduce excessive voltage drop) and hasn’t been de rated (i.e being run under insulation or certain enclosed spaces) which reduces the ability to dissipate heat (all cables produce some waste heat when in use due to resistance in the cable) so the cable seems fine as long as it was specced right when first ran
Now onto the last part and without deep diving into breakers as there is a lot of different things to look at, ignoring the type of breaker A,B,C,D (how long in seconds it can last dealing with large startup surges in induction motors and other appliances) the other thing with breakers is they dont trip instantly as soon as you go above say 32A on a 32A breaker. A slight overload on a breaker could take hours for the breaker to operate whereas a massive overload from a dead short on an appliance will trip it near enough instantly (seen this happen from personal experience with a dryer and heating element that shorted out as both sides touched which popped the 32A breaker within a second)
since the water heater is only been run for short periods of time this will be why the breaker hasn’t tripped but i would be wary of it doing damage over time to the breaker if repeatedly done due to it potentially overheating/causing damage internally which could cause it to malfunction. The breaker is undersized for the appliance so it needs replacing (next size up i know of is 40A). Me personally i wouldn’t use it until its sorted but if its something you cant go without then i would recommend keep the usage time as short as possible and use it as infrequently as possible.
I want to preface again that I’m not an electrician but have a fair understanding of the more general side of it so please don’t take my word as gospel and I hope that a qualified electrician stumbles across this post and can offer a more detailed insight into it that knows a hell of a lot more than I do
I know this might be irrelevant but i have yet to find an answer to this one question.
In T-T System, should we connect the consumer earthing cable (coming from ground rod) with the neutral at the consumer unit?
No! That would void the whole point of providing a separate earth and would also cause some (normal, non fault) current to flow through the installation earth rod back to the earth rod at the source transformer/substation.
Aren't TNCS systems installed with PMEs? So in theory the return currents that cause the voltage drop in the CNE conductor are run to the mass of earth locally?
In most countries yes.
In the UK, there is no local earthing for TN-C-S supplies.
Thanks
I would personally introduce an earth mat as an extension to the TNCS until I reached an impedance of at least 10 ohms.
MAXIMUM 10 Ohms, NOT at least!
I am seeing some weird stuff at my location since last 2-3 days.
At night I saw an neon led light glowing faintly even though switch was off but appliance was plugged in. I though might be some loose neutral somewhere.
I tested with a multimeter and here are the readings
Line to neutral 248 volts
Neutral to earth 111 volts
Line to earth 350 volts
This is strange. How can line to earth become 350volt. There is no issue on any appliance as line to neutral is ok. In morning it got fixed somehow and voltages becomes normal, led stops glowing. But again at late night it starts with almost similar readings. It's the same thing on another house on different phase. Any idea what causing it?
Probably a faulty neutral on the supply to the property, and it shows up at night because the load on the whole system is lower then.
It needs to be fixed as a priority - contact the power company / network operator.
@@jwflame ok, will get it checked.. Thanks!
Hi I wanna change a single socket to a double socket. wires is way to short to fit the double can I use a connector strip block. I know I can get other sockets but the sockets are bought now
Better to try to get some slack on the cable if possible, if you have to extend do each individual core with a compression crimp joint which are maintenance free
@@tonywebb9909 what type of joint is that
why does uk not use 3phase install for domestic. We have done that for 50 or more years in Denmark. showers get warm water from the central heating system and hobs run on 400V. keep the amps down
All I have seen in DK are (3-phase) TT systems. Why is this common in Denmark?
No need for 3 phase, there isn't any equipment used in homes that requires 3 phase.
Most UK homes are heated with gas.
@@jwflame Our village didn't get gas until 1989, many of the houses built in the 50s, 60's and 70's had storage heaters, so almost all of the houses have a 100A incoming supply. 3 phase would have been a sensible route in those instalations.
@@cambridgemart2075 The village I live in still hasn't got gas! I heat with an oil boiler though I think the house must have had night storage heaters before I bought it as there were three incoming wires, a neutral and two that ended in main fuses, though only one connected to anything on the load side..
Is the purpose of the protective multiple earthing is to keep the neutral wire at zero earth voltage?
Yes, although multiple can mean as few as two.
@@jwflame Thanks John.
I am just about to install a hot tub on a tn-c-s. Would there be a issue with installing a ground rod near the hot tub with the earth linked into the main cpc from the tub. Basically a supplement to the cpc ground from the hot tub. Does anyone have any ideas on this
Not a problem with that, and it's actually recommended for TN-C-S installations to have a supplementary earth electrode as from 18th Amd2.
The cable from the main earth terminal to the electrode will need to be sized appropriately, which may be larger than the CPC in the cable to the hot tub.
I take it this means the UK does not require earthing electrodes bonded at the service entrance? Here in the US code requires at minimum two earthing electrodes connected at the N-E bond. As well as requiring swimming pools and all exposed metal be separately bonded to the earthing system.
No, unfortunately not. They are permitted, but optional, so are almost never installed.
In the past, most properties had their gas and water pipes supplied via underground metal pipes which were bonded to the supply, and acted as electrodes even though not intended for that purpose.
More recently those underground pipes are all plastic, so there is often nothing at all connected at the supply point.
If you have your N-E bonded to an additional local earth electrode, wouldn't there be a persistent current between the N-E and local earth?
Understanding Earth ( cable ) theory is a Degree in all it self.
I have to explain alot of this many times to people still think of Earth as 0vdc or ground. Ground is not Earth.
People find it more confusing when doing ICE products ( car / truck etc ). As the tyres on the vechicle are plastic rubber and therefore isolates the vehicle to Earth.
I always equate E to N expect a risk of 30V, a fizz.
Then there is Star / Delta Earth cable diferences when spilt phase between three houses ( and lampposts ), and then if someone has their own additional copper Earth spike on their property.
And then the topic of Earth leakage from surge protectors ( capacitors / inductors ) and chinese cheap buck convertors and dodgy transformer applicances or dodgy plugs from your neighbour giving spikes and leakages back feeding.
Way forward in a theory maths we would need a IsoT with no Earth linked and throu UPS, then maths would be true.
It would surely be 18v to earth, not 9v at the last house
It's 9v
ibb [dot] co [forward slash] 5k9VnF9
ibb.co/5k9VnF9
@@jwflame Thanks. It wouldn't let me post the link.
@@spudhead169 What software did you use for that?
18v difference from start at tx, not end house E.
Last house, L N at AC so 9V and 9V
as N is E, E is a distance of resistive cable connected to N of which throu the resistive Planet-Earth ( mud and rock ) connects back to E at TX, of which TX E connects to N.
In all another electrical circuit that never gets drawn on circuit diagrams.
Its get even more confusing when you are dealing with virtual-Earths and isolated removed Earths in Iso-Transformers, in High frequency or super high voltage SMPSUs.
In all eletric ( electr-ic) is flow of eletrons, which want to return to the start ( a circuit ). Volts are the difference in between to item.
Remember as its confusing, two difference AC or DC appliances or circuits can have a voltage difference between them even their case Earths, hence in some locations you addtional Earth Bond the white good appliances just like Water pipes. On production lines you may do this too, or in Casio and Timex they passed 50V DC ( yes DC ) thou their site-Earth ( Virtual not Planet-Earth )( and delinked N to E on sites Iso-T), to stop static damage to their stuff they are making. ( floor was insulated with pure rubber 1 inch thick, available mainly from RS to stop electons from Site-Earth going to Planet-Earth ( returning to TX, making a full circuit of electons ) which would be shock risk to workers if did).
Wouldn't the 3 houses usualy be on different phases and the neutral current would only be flowing in the short neutrals beween houses?
Adjacent houses are often on different phases, but that 3 phase cable will typically supply dozens of homes along a road, each with a single phase connected.
@@jwflame But statisticaly all of those houses represent a ballanced load to the substation so the only neutral current flows from the street cable to the individual supplies and between any points of inballance in the street cable. any neutral currents only act along a short length of cable. The net current in the neutral back to the substation is zero.
@@elanman608 Can be, but with modern high harmonic loads neutral current, even in a 3 phase system that is balanced phase current wise, will be high, approaching the same current as the phase current, and can even be higher in some cases. Even though power factor correction is applied at the load, there is high harmonic current flows in the lines.Neutral current being zero only applies really with pure resistive loads, not with loads that use either active rectifiers to generate DC bus rails, or just plain rectifiers. There you get current spikes that are harmonics of the mains frequency, and these do flow in the neutral. They go up the supply system to a larger substation, that has power factor correction capacitor banks, that filter them out.
@@SeanBZA or to put it simpler, for loads that draw at the peaks of the waveform, like a smoothed rectifier, if it draws current for less than 1/6th a cycle on the positive and negative, the current draw on one phase is always at a point when the current on the other two is zero, and there Is precisely zero cancellation between the phases because they're never drawing current at the same time.
see 6:28 mark...why would 1 live (phase) be distributed to 3 houses? Normally each house would get a single phase L1, L2 and L3 (or red, white and blue), the neutral / earth may be common (split) to all 3 houses though! Therefore the scenario being described should never occur!
The three phases are distributed among the houses, but one transformer will supply many properties, not just 3.
A typical housing estate may have 100+ houses connected to a single transformer, with 30+ on each phase, all supplied from one cable.
Usually wouldn't the neutral have less difference to earth due to it being balanced by the three phase supply and potentially having less resistance than the lines if the sheath is in parallel. However a phase load mismatch could give a larger difference of earth relative to the shared neutral.
If the property had a 3 phase supply, and it was balanced, then yes.
However the majority of homes in the UK have a single phase supply with a 2 core cable.
@@jwflame Whilst the houses are single phase, most are fed by a short 2 conductor cable from the three phase supply in the road, with the phases supplied alternately to sequential houses, sharing a common neutral. I was thinking that shared 3 phase neutral in the road would have less apparent voltage drop than line unless there was a significant phase load imbalance.
All depends on whether the phases are actually balanced. With all single phase loads connected in the different properties, there is no way to know when or if the three phases have a similar current.
@@jwflame I've had the task of sinking generators onto substations many times it's not unusual to find 150a diffrence across phases
I think you may have got this slightly wrong unless you're describing say, phrase 1 distribution around a block of flats for example, but in an 3 phase supply network to homes the neutral only carries the unbalanced load ( my neutral return will pass though my neighbors home when phase is at 180 to my phrase. Also the neutral will be bonded to the mass of earth at the feed to every property in an attempt to clamp it to 0 volts or as close as posable
In fact loosing the neutral within the supply network won't result in all class 1 items to become live at mains voltage, the voltage will become very unstable ( if say 242v supply drops to 200v then 42v will rise on the neutral ).
Installations in the UK do not have any earth rods / electrodes at the property, and almost all of them have a single phase supply so unbalanced loads are inevitable.
Hi john. Thanks for reply, I love you're Chanel! , and great deal of respect.
I'm referring to the DNO infrastructure, the 3 phase network, every house that is single phase connected to one of the 3, your next door neighbours will be on a different phase .
Take a look at overhead cables feeding a property that's on a tn- c- s there will a 16 mm single core wire running down the pole in to the ground, that's the neutral bonding wire. Its there to keep N-E to 0 volts,
Every house is connected directly to to one of the phases ( staggered ) and not looped along one phase as you was illustrating
PME is fun but not when it electrocutes you - JW
Interesting, the more I see information about power systems in other countries the more I realize the US is not all that backwards. My house may share a transformer with a couple other homes, however each has a home run to the transformer. The US was pretty behind at one point, I think the playing field for safety has mostly caught up. Insurance companies drive most of the progress.
In the UK, it's common in urban areas to have a single transformer that supplies dozens or even hundreds of homes mostly with underground cables.
Rural areas usually have smaller transformers for one or a few properties, overhead cables are more likely there.
@@jwflame It's just interesting to hear that they sometimes chain them house to house. I'm not saying that doesn't exist in the US, I've just never seen it. Rural areas in the US have smaller pole mounted transformers with runs from the transformer to a few homes. Always a star type configuration. Thanks John, you should look at some of the videos from Mike Holt related to problems in the US with earthing. The same type of voltage gradient issue exists, just for a different sort of reason.
@@jwflame Common to have 200kVA transformers and feed a short section of street, or a 1MVA for a cluster of high rise and high density housing, though the age of the transformer fleet often has you with 3 200kVA transformers right next to each other, as the load grew, as it is a lot easier to splice in the 11kV feed, than to replace the transformer, as often they are in buildings with poor access due to construction, or limited space.
Across the road a 400kVA unit, and 20m away a 300kVA unit, on the same feed, because the 300kVA supplies a single complex, and it was installed relatively recently. Unlike the 400kVA, which dates back to 1900, when it had a, now disused, mercury arc rectifier room, for when it was used to supply traction power for trams. The old DC cabling is still mostly there in the ground, and was still, till 2009, fed up the street poles.
@@SeanBZA I used to work for LEB. Our ground work contractors used to love it if we had to clear the ducts for a new cable and we were pulling out old DC stuff. Loads of copper in them, great for scrap value.
@@Raysnature No ducts here, only direct buried cable. most of it is old steel tape wrapped paper insulated cable as well, at least where it has not failed and been scotchcast to PVC SWA cable. My feed is still the original lead wiped steel taped paper cable from 1950, though it is slowly leaking out the oil impregnant. Only going to be changed on failure, as they will need to do a good bit of trenching and drilling to bring in the new cable.
I've got a bit of a problem. A customer with OCD is uncomfortable with a dual light switch arrangement. She's bothered by one of the switch positions being reversed due to how that switch circuit works. I'm not aware of any solution to this other than those electronic smart home switches, but she doesn't want those; just regular (looking) switches. I'm good enough with engineering and electronics to be able to construct something out of regular switch plates, servos and the like but the result wouldn't be BS compliant. Anyone have any ideas? I really hate telling her it can't be done because she's the sweetest lady I've ever known, albeit a little strange due to her OCD.
Retractive switches with an impulse relay located elsewhere. Both switches will always look the same regardless of the light being on or off.
Of course if it werent for penny pinching there would be proper PME and every group of say 5 houses would have an earth rod to bind the neutral down... and mitigate a lot of this crap...
So is the 9v between the earth 🌍 and the other earth unmetered?..
All I kept thinking was free electricity.. :)
Hmmm interesting thought could we utilise this
Nope, like video said difference occurs only when current is flowing on the normal circuit, so that means you pay already for it
@@samiolmari3821 how are they going to meter the power inbound on the supply. It must be metered from the floating ground reference.. so that floating ground which is positive to the real ground must be outside the meters ability to read it, maybe..
Or would it depend on the meter?..
@@TheWebstaff Just think for an moment what it means "current needs to be flowing" (in normal circuit) for voltage difference to exist between earthwire and real earth...
That current is metered, it's already flowing through the installation.
Electricity meters measure the current on the line conductor. Whether that current then flows via the neutral wire, through the earth itself or some other route doesn't change anything.
Good vid that. I had a very short explanation without the numbers but rough sketch from an old engineer on a building site at Eastern Electricity Board back in the early 80s with regard to PME, how good it is but how dangerous it can be if not connected properly using outbuildings and it is because of this old boy, I never forgot that 10 minute lecture when I was a mear squat of an apprentice, that I always have stopped the earth connection at a shed or garage in an insulated C/U and used an earth stake with RCD.
Do you remember them good old days when you could talk to the real engineers of the UK owned electricity board guys who were from the real world of experience and not just some young spotty twat who just come from a weeks electricity awareness course and things he knows everything because he's got some French owned utility company fluorescent jacket on.
And I ain't got a chip on my shoulder.
Young spotty twat ??
Don't hold back ..............
Best comment yet.
Hi
When is an earth not an earth
When your on Mars lol
please dont lick a 9v battery, a handful of people die each year from exactly that...
you wont die from licking a 9v battery. At worst youd burn your tongue. To kill you requires either a lot of current to cause you serious enough burns to be fatal, or for the supply to be AC and flow across your heart, causing fibrillation