Actually, technically No. Current doesn't flow in a conductor, it flows around the conductor, or so i was taught at trade school. Current in the neutral must equal the current in the active, how else does an ELCB work!
Don't know how UK electric works other than that you lot use 50 Hz instead of 60 Hz, but in the US you can't have 3 different devices share 1 neutral with 3 phase power. It used to be allowed, but the NEC was changed in 2014 I think. It's a lot of fun trying to fish 2 new neutrals in the old conduit to upgrade old buildings. (not) For fear of undiscovered nicks/shorts when the power is turned back on, oftentimes we just hook new wire with additional neutrals to the old, and use the old for the pull line to install the new and then recycle the old.
A couple of gotchas with 3 phase neutral: 1) If there is a fault the absence of a neutral connection can allow overvoltage on the phase conductors without tripping breakers and the risk of shock or fire in any connected loads and 2) someone might connect a 3 phase + neutral appliance like an industrial heater to single phase power, joining all 3 phases together and tripleing the current in the neutral. Best case the neutral wire burns out, worst case the building burns to the ground.
@@markhill9275 OMG OMG OMG....Current doesn't flow in a conductor, it flows around the conductor,???? matter, atoms, electrons, neutrons... learn your lessons again
I just discovered this channel and I love it. I´m a Electrical and Computer Engineering student and love all things related to power grids and house installations, your explanations are more on a "practical" rather than theoretical approach and I just find it much easier to comprehend. Amazing work!
An outstanding presentation. I am a retired electrician and most of my work was done on 480 VAC three phase control circuits. I worked with maintaining large 50+ horsepower 2-speed motors and things like that. I also worked with DC traction elevator motors. I found it to be very enjoyable work. Your presentation is spot on!! I just subscribed so I will be seeing more of you. Cheers!
For anyone having trouble envisioning this, it's a bit easier if you start with something like American (two phase) house wiring, which comes in from the pole transformer as 240V, but with a center-tapped neutral wire. That means that neutral to either live conductor is 120V, so you basically have two 120V circuits, but each one is 180 degrees out of phase with the other (and typically half of the house circuits will be wired to one side and the other half to the other side). Because of this, if you need more than 120V for some appliances (such as many stoves, water heaters, EV chargers, etc), you can just connect them across the two different "live" wires to get total of 240V instead. In that case, you don't need the neutral wire, because all of the current going in on one side is balanced by the (exactly opposite) phase on the other wire going out. But it also means that on the neutral line going back to the pole, there may or may not be a lot of current, depending on how well the loads on the different house circuits are balanced. If you've got the same amount of stuff going on one half as on the other half, then all of the current will go "in" from live A to neutral, then from neutral to live B and back out again, and there will be no net current on the neutral line. However, if there's more load on the A side than the B side (or vice-versa), then all of that excess needs to go back out the neutral instead.
FFS! If you have trouble envisioning it then go back and re do your entire electrical training! It's that basic a question. And if you don't know the answer to it, you shouldn't be anywhere near mains electrical installations, even if you are "qualified". Because for you not to know the answer means that: 1. You have forgotten your basic electrical education, and 2. That you don't really understand electricity.
@@greenpedal370 Yes, he is quite correct about their being 180 degree phase shift between the two lines in the US split phase system. If you know enough about sine waves and electricity, you will realise that 180 degrees is the only way that is possible. If you think he is wrong because you think it should be 120 degrees, then that is certainly incorrect. 120 degrees phase shift between phase conductors only occurs in 3 phase systems. And that is because they physically position coils around in the generator at 120 degrees around the rotor. In the US split phase system, the phase signals that are distributed to consumers do not originate from the power station and generator, they are produced by the down stream distribution former and is a result of how the secondary windings are connected. It's very different to 3 phase.
This could also be drawn up as vectors. The phases are 120 degrees out of phase, a balanced load drawn as vectors would also show 0amps, and an unbalanced load would result in a vector length equal to the amps drawn in the neutral. That's how I learned it and understood it best in school, but this was also a great explanation! Nice and simple, keep it up! :)
I was trying to explain this to a cocky technician, who was 15 years senior to me. He was having none of it. I designed a control panel with a 3phase 2.5mmsq supply. There was a 16A single phase breaker on each live. His argument was that this arrangement would put 3x 16A=48A of load on the Neutral (2.5mmsq) wire. To prove he was right he even rang his mate, who was a lead in Intel, and they both were in agreement on this. Good guy though.
The neutral wire is the return path for unbalanced current in an AC circuit. It is not additive, it is subtractive. Put an amp clamp on the neutral wire of a nominal load, and you’ll even see that the current on the neutral will be equal to the current on the line wire.
@@PORTEnSious yes wire size affects current flow as smaller wires can introduce greater resistant. But this is effectively in series so affects current through the whole of that circuit. Same way an appliance would affect current. V=I/R But that doesn't really affect the topic in the video. As what ever current passes still follows the rules they described. Hope that helps
To be fair if it was the same phase they'd have been right. I think some brains just don't like coping with multiple phases. You'd hope better from an old boy though. 😁 They've had AC since Tesla lol
@@PORTEnSious Wire size doesn’t limit current flow, but depending on the size of the load vs. the undersized wire, what will happen is the wire will not be able to dissipate the heat generated quickly enough, and will cause rapid deterioration of the conductor insulation. Also what can happen is the the wire itself can melt, most likely at the point of termination closest to the load. A real life example would be a water heater that pulls 23 amps and is being fed from a 30A breaker @ 240V, but instead of using #10 AWG copper wire (which is rated for 30A using the 60°C in the NEC ampacity table 310.16 for residential applications). For the sake of this example, the installer uses #14 AWG copper for this installation which using the 60°C table of NEC Art.310.16, is rated for 15A maximum. In this situation, you have 23A running through wire that is rated for 15A maximum. In this install, you would definitely find overheating, burnt insulation, damage at the breaker and at the water heater disconnect switch, or directly at the water heater itself. One thing I forgot to mention is the ampacities mentioned are maximums for periods of time 3 hours or less. There are specific rules in the NEC I don’t have time to mention, but generally if a load is intended to be ran for 3 hours or more at any given time, it is not supposed to exceed 80% of the breaker capacity. For example, if a shop heater is rated to draw 24A, the breaker MUST be rated for 30A (30X.80=24A).
I challenge you to actually disconnect the neutrals with running equipment 🙂 Actually that would be a *really* bad idea. Happened at work once in the distribution board (faulty installation, took a couple of years to fail after the building was constructed). The insurance claim was I believe in seven figures and we were super lucky the building was not burnt down. Helped that the fire station was just across the road and they responded in under 90 seconds.
@@efixx For those that don't realize no neutral and all the lives float to 415V AC. The fire was started when the 400V rated capacitor in the power supply of a PC decided that being at 580V (415*sqrt(2)) was not good and flames came out the back of the PC (the slowmo guys have some nice footage of capacitors giving way), and set alight to the noticeboard behind (this is why the mains smoothing capacitor in a SMPS should be rated for 600V). The reason for the really high insurance claim was this was a biosciences lab and at lot of the very expensive equipment didn't take kindly to the 415V AC feed to them.
If you had just one heater and nothing else there would be no current flowing. If you had two heaters each 80 ohm (720 W) you would have 415 V over 160 ohm. That is 2.6 A and 1080 W (540 W each). That is if you have three identical resistors on a star connection with the neutral is connecting one reduces power by a third and two by 2/3. If you do not have a neutral then disconnecting one reduces power by 50% and two by 100%. The real problem is that if you have some other loads in parallel like an incandescent bulb with 960 ohm. If it if gets in series with the 80 ohm heater at 415 V it gets 383 volts, i.e. it gets 2.5 x the power and will not last long. If you disconnect the neutral upstream from the main panel then the voltage in it gets to the earth wire.
Had the neutral at the substation vanish with thieves, and the phases started to diverge on all the houses. Had the UPS start to warn about overvoltage, so measured mains at 270VAC. Immediately turned off all loads, and turned off the mains to the entire home as well, then went to the meter room and checked phase voltages. One was at 270VAC, one was around 230VAC, and the third was around 170VAC. Turned off the entire building, and got on the phone to the metro about a loss of neutral at the substation. Took them most of a day to fix it up, and they came back the next night to do it again, so they put up the steel doors instead of the wood, and welded all the cable access covers on, that they used to strip the SWA feeder cables leading to the street.
Nice video Funfact In Norway we have been running our mains network for 100 yrs with no neutral! Neutral is not absolutely needed. With no neutral and the loads in a dela konfiguration, that is all loads are connected between live 230V wires, the return currents ‘fines its way’ via the other wires. After 1995 all new houses in new areas are connected via 3-phase 230/400V TN networks, now with a neutral wire.
Yeah, I did learn this back when doing my C&G part 1, 2, 3. It was really nice to see it all again in video format. I think we did it all in formulas back then.
This is spot on . I think most people missed the fact that , even though you don’t need neutral , and depending on what you are running , and in this case 3 units 1 phase heater: it is safer to run a neutral at 1/3rd the max amp capacity , in this case and if in the event if one of the 1st phase heater encounters problems .
It would appear from the video that you need the neutral to be the same size as the phase conductors, as if one heater fails you need to be able to carry the full rated current of the phase conductor.
This is exactly what I was wondering for a while now so thank you for explaining. I knew three phase motors didn't need the neutral because it was a balanced load but for some reason it never occurred to me that heaters would also work the same for some odd reason. Clever stuff.
Interesting demo. Will be valuable for all those domestic sparks that never get involved with three phase systems. Came across a large lighting circuit like this some time ago, gave me a bit of a head scratch till I realised that the neutral current will never exceed the current of one phase
Those domestic sparks that have only undertaken the domestic installation courses are not allowed to do 3 phase work (in that they are not allowed to do industrial installations). And if people are qualified to do industrial electrical installations then they have been trained in 3 phase and should not need this video.
You woke up on the wrong side of the bed Dean? The video could be helpful for people who are in the process of qualifying for carrying out industrial installation work? 🤷
Do you mean "domestic spark from UK" only. All other domestic sparks around the UK (and commonwealth and U.S.A. ) use three phase connection to every house/garage/shed/fabric hall since Siemens & Halske around 1880 use 3phase AC and build the generators around the world!
That's the reason the 400V continuous flow water heaters with 22 or 24kW, that are popular here in Germany for electric water heating for showers, don't require a neutral at all. In most cases we still install a five core cable. The five core NYM-J is only 1€ per meter more expensive than the four core one. Neutral isn't connected of course, but still available if it would be required in the future.
It’s a really good idea to pull the neutral always for future use, here in Finland it used to be acceptable to wire 3-phase sockets with no neutral, if they were intended for a large machine, it’s really fun when you rock up with a portable distribution board to only find that they left out the neutral. And it’s no fun either to have to install transformers for 400/230 just to get some new-fangled boiler with a control board that needs a neutral working. :)
@@sstorholm Not the motor itself, but eventually the electronics that regulate the speed of the motor. And maybe contactors if you want to reverse the direction of rotation. And also possible, the future replacement requires for other reasons 230V in addition to 400V. Unlikely in industrial applications, but not unthinkable, and in domestic applications this can always happen. I remember my grandparents had a Perilex socket outlet (three-phase socket outlet )in their bathroom for the washing machine. The plug always "wandered" from the old to the new washing machine because it was the old rare 25A version.
@@sstorholmThe motor does not, but the control circuit may. Many EVs that insist on seeing a Neutral. A 1-phase Renault ZOE wil not charge unless one of the wires are a true Neutral and you need a 230/230V transformer with one of the secondary wires connected to ground to charge your car!
Many moons ago I was working in a computer factory (not as electrician :) ) when a cloud of acrid smoke tripped the fire alarms. Turns out the busbar chamber had a reduced size neutral, as the load was considered pretty well balanced. Ad Hoc alterations had seriously unbalanced the system and the neutral was glowing red hot with all it's PVC insulation burnt off! Turned off and fixed, with half a day's production lost, but could have had much more serious consequences.
The neutral over heated due to harmonics. Most times it is the 3 rd harmonic. It is a result of having loads that are non linear to current. That is variable frequency drives, computers, discharge lighting etc.
Thanks for the current measurement on the neutral with the two loads on L1 and L2. Both because it's not intuitive, and will force me to interpret the KCL and the desmos graph on my own as an "exercise for the reader". Where in the circuit are the neutrals of each of the individual phases physically connected? Within each of the outlets on that piece of plywood? The diagram at 5:36 shows the conceptual drawing; but where is are the physical connections of that neutral in the Y-config?
Always remember a site we took over from a previous company. They told the customer that all the 3 phase circuits had no neutrals and they all needed rewiring… just showed lack of knowledge on the subject. Maybe more should be taught about things like this before people are let out on the wide world 😅 Neutral in a 3phase is generally found if the item has other elements eg control panels and other single phase components with in the 3phase item. Great video guys!
Your video on your “Joe Robinson” channel on this same subject (a few years ago) was the moment the penny dropped for me! Very well explained Joe & @efixx👏
So when you had two heaters connected and measured the current on the neutral, it wasn't the same as L1 + L2 because it was partially mitigated by the opposing phases, but not completely as it was when you activated the third heater? - fascinating.
I've come to the conclusion that I am 'Electro-blind' !!! I love videos like this one and it is extremely well presented but I just can't get to grips with the physics of electricity lol. Keep up the good work and I'll just be happy I can change a 3 pin plug!
I would clarify slightly in your eater example, if you disconnected the 3 individual neutrals all 3 heaters would switch off but disconnecting the common point they would run in a star configuration. I know most viewers will know thats whats happening but just for clarities sake.
@@brianhewitt8618 star points are an interesting thing as is generator earthing which is a related subject. Not sure if efixx will cover them but maybe sparkyninja?
Hello, I just looked up this information and found your channel. My dad is an (old time, retired) electrician and has taught me to do basic electric work. I replaced a ceiling outlet (lighting) and instead of turning off the circuit, I just turned off the outlet as it's and old house and it's supposed to only have 2 connections (phase + neutral, no earthing) in most places. Turning off the phase should do the trick, and even if there is some leakage, it should only tingle. I verified everything with a basic "glow lamp" style seeker. No phases. And then verified with a multimeter - No current flow from L1 to Neutral. However, I noticed the neutral had 2 wires attached. That was peculiar,but I thought it might just be sharing a neutral with some other light or WTF knows? It shouldn't be an issue. When I disconnected the L1 from the ceiling outlet = no issue. When I disconnected the neutrals, small spark and the lighting on the walls in that area of the living room (supplied by wall outlets) turned off. Interesting. I shat my pants, stepped down from the ladder, took a moment to check myself, wondered why the RCD didn't trip (obivously it only sparked, didn't touch me in hindsight) and then turned off the entire house main feed. I'm not messing around anymore when neutrals and phases are mixed around everywhere. Anyway, I told my dad and he refused the possibility of electricity in a neutral. I told him electricity is defined as a difference in charge, and there should be current flowing return in the neutral. Now I understand it better, and I'll show him this video. (Also, I'm the EU with a proper RCD and I use VDE tools with the 1-hand-behind-the-back principle when doing semi-stupid shit like this. Worst case is going to be a zap until the 30ma RCD cuts out)
It's simple. The 3 phasers are vector quantities and therefore add up to a resultant vector in the neutral depending on the magnitude and phase displacement. Electricians were taught this as part of their apprenticeship in my day...
Very interesting and well explained. However, if the incoming neutral becomes disconnected as I have experienced at a heritage railway, where the unbalanced loads caused serious problems with some devices burning out and other loads suffering low voltage. There seems to be no protection against such a problem and the supply company sometimes won't admit there is a fault.
Apprentice here. Excellent video, thank you. Only problem I see here is that, most (Yank) electricians have no idea what the sine waves represent, on the X & Y coordinates. It’s just a bunch of squiggly lines. It would be helpful if you clarified it, more than briefly mentioning that it’s current (w/respect to time) so viewers can fully grasp what’s going on in the graph.
How do you know most “Yanks” do not know what sine waves represent? Is it because you watch videos of people that say, “I’m not an electrician, so don’t do what I do” and show them working on 120/240 volt single phase electric system?
Great video. Well done. But it is clouding up the subject a bit. Of course, using three phase for single phase devices happens all the time, but single phase devices use one two hot lines. 120V and 277V devices use one hot line and neutral. 208V and 240V could be either one hot line and neutral or two hot lines and 480V is always two hot lines (all examples are single phase). I would like to see this using a single-phase supply, L1 of the 240V single phase supply wired to all three heaters in parallel, then check the neutral amps as each heater gets energized. A previous comment said the standard residential supply is two phase because of the two hot lines. That is wrong. The standard residential supply is 240 Volt, Single Phase. Best Wishes. Hope you keep up the good work.
It is true that passive loads, resistive or inductive will balance out and there will be no current in the neutral. However with loads where the power factor is less than 1 and the shape of the current trace is wildly different than the shape of the voltage trace such as most switch mode power supplies without active power factor correction, you can in fact have a greater current on the neutral than any of the 3 phases in the circuit. Something to consider for installations where the bulk of the power goes through switch mode power supplies such as variable frequency motor drives or datacentres. But active power factor correction is getting more common in such power supplies nowadays so their current draw is becoming more sinusoidal instead of only drawing current at the very peaks of the voltage which when the load is large turns the sine wave into more of a square wave.
One way of thinking about this is that the neutral current is the total phase imbalance. One phase loaded(= 1kw imbalance). 2 phases loaded (= 1 phase = 1kw imbalance). 3 phases equally loaded - no imbalance.
You can think it as an equilateral triangle, When you go one side you are one side away from the start, then after the second it is the same but the third side gets you where you started.
If your circuits are not balanced in the breaker box, you can get current flowing on the neutral line. Also, if the protective covering on the wires feeding your breaker box crystalize, you can also generate current flowing on the neutral line. You can argue with me all you want, but I learned this through experience when we installed a minicomputer in our newly renovated building. The computer was blowing boards every month, so we put a line analyzer on the system and discovered current on the neutral line. Apparently, computers do not like current on that line. Upon diagnosing the problem, we discovered what I mentioned above. Once we fixed those two problems, the current was no longer found on the neutral line.
in a sense, the protective covering being crystalized creates more resistance big enough that it creates an imbalanced load. In real world application tho, no circuit is ever balanced. A balanced load is more of a theoretical circuit .
do the same with 3 x non-PFC power supplies (like your laptop's PSU) Even when all lines are balanced, you shall see a current in the neutral. The 3rd current harmonics are summed up in the neutral
The heaters are rated at 230vac input. Line to line voltage is 400vac. Square root of 3 (phase system) is 1.732 and is always applied to power calculations. 400vac over 1.732 is 230vac, which would be measured between any line and the common point. 3 phase resistive load; Ib = P/Vx1.732
Question from a layman. If current is flowing thru the neutral circuit why can't you recycle or re-use it, & does it "return" to the supplier or could you feed it into a battery or transformer intercept without "consuming" any more celectricity ?
Howdy. Yes. If the load is a delta configuration no neutral is needed either. The currents need not be symmetrical. It is defined that the neutral needs to be only half the phase cross section from 16mm2 upwards. That is true in most cases. However, powerful solid state frequency converters may generate very strong harmonics. Some harmonics cancel each other but some get added in the neutral. The neutral rms may be way higher that what half a cross section can carry. With converters the neutral should be the same as the phase at least to 25mm2 copper. Preferrably to 35mm2 copper even. In modern converters efforts have been made to decrease the neutral currents. Always check the specs for what cross section is needed for the neutral. Regards.
Why was the current the same on the neutral when two heaters were hooked up. If you explained that I missed it. Also how does current flow without the neutral connected. I know 220 doesn't have a neutral but unless Im mistaken each leg reverses acting like a neutral.
Hi what is be the most likely cause of over-voltage in a 3 phase system? One of the phase was found with voltage of 385V and it tripped the CBs and caused damage to equipment that were connected to the phase.
If you're interested in electricity kirchoffs law is pretty interesting as is thevanins theory, not super heavy in maths but worth a look in my opinion
In my 3p installation (French farm house), I am required to keep the three single phases as balanced as possible. If I don't keep them an average over the day of no more than 30% from balanced, I am charged for the imbalance. Actually the power company use a average of averages over a rolling ninety days with each day being the final day of the window - a rolling window of usage, if you will. It's a very fair way of calculating poor usage of multi-phase mains. In this case, a current sensor on the neutral is being used to discover the extent of any imbalance rather than having a meter on each phase. In reality, I have access to this data, including usage on each phase using a IoT meter I built myself which contains four current sensors attached to an Arduino with a wifi module to send the details in real-time to my own metering software as an MQTT stream. I then create a graph using Grafana this to show when imbalances occur and can adjust the loads on each phase accordingly without having to guess which is underused. Not too long ago such metering hardware and software would have cost a fortune. Now it is possible to do it for a few quid.
Hi, great video just have one question on the neutral currents . In a 3-phase load I think i understand the concept of how the appliance uses the other 2 phases as a return path as opposed to the neutral. However in a situation such as in this video where 3 separate single phase loads are connected. How can the appliances use L2 or L3 as a return path? If the neutral were to be disconnected then surely there would only be 1 line conductor to each appliance? How would the appliances continue to operate if the other phases are not present at the appliance to act as a return path? It seems like I’m missing something here but I’m just scratching my head at the idea of an appliance operating with only one single conductor at point of connection.. hoping you guys can help me on this one hope I’ve made the question understandable!
you're probably thinking that all 3 currents at any given moment are coming out the source. This is impossible in 3 phase. What is really happening is, at one moment in time, only TWO phases have current going out, and combine (vectorially) to return on the 3rd phase. For example, at one moment, A and B going out and combine to return on C. Next moment, A and C going out, and combine to return on B. Then next moment, B and C are going out and combine to return on A. And repeats. Of course this is in the context of a balanced circuit. Hope this clear things up
PME systems (TN-C-S) effectively remove (minimise is more accurate) any current from the Neutral in the DNO's supply side network but obviously that is not the case in the customer's Consumer Unit
With each customer on a TN-C-S system the current from the Line to the Neutral is the same. However, over a large number of such customers on the three separate "Phases" the total/residual current on the "Neutral" conductor will be quite small - hopefully, zero.
Different when it comes to Harmonic distortion, particularly the 3rd harmonic. These harmonics are the result of nonlinear loads that convert AC line voltage to DC, i.e. frequency converters, PCs etc. This causes a much higher current to flow in the neutral even in a balanced designed system, thus needing to install Active or passive harmonic filters to take them out and balance the load again or simply oversizing the neutral conductor to exceed the phase wiring by 50% to accommodate the higher current
Yes, in forward phase theatrical lighting systems, neutral over-current can be a big problem! Basically, at certain settings, the dimmers may all be drawing current near the end of the half-wave so there is no cancellation. The result is that the neutral conductor is carrying the highest current load. In the US, NEC requires such systems to oversize the neutral conductor. As harmonic filters would trow of the Zero-Cross Detectors in the dimmers, oversize is the only solution.
In the US, high harmonic loads are required to have the neutrals doubled in size to handle higher amperes on the neutrals. Special transformers are also made. Best wishes, Kevin
My predictions for that experiment were: - Current on neutral equal to current on live if one is turned on - If two are on, current on neutral will be about halfway between one of them, and both added together - If all three are on, no current on neutral Now, I did watch the solution before writing this, so I know I got the second one wrong, but the idea was correct. Because both are on, there is an additional return path, and so less current needs to return through the neutral. If all three are on, the only current you would expect on the neutral is the difference in consumption of the heaters. Since they are all very similar, you wouldn't expect very much. They are all on different phases, so there is always a return path through one of the other heaters. ...now, I am writing this after seeing the solution, but before the explanation... so let's see how wrong I got that, lol
“The answer is Yes!” The problem is when the neutral conductor of the load losses its connection with the neutral line of the power grid. I’m from Bulgaria. In the backward years (40-50 years ago) our power grid was 2-wire one - Line and Neutral only, without Ground wire. All loads with metal housing were “neutraled” instead of grounded because the power sockets were bridged to the neutral instead of separate ground wire. And there comes the problem - when the neutral conductor is interrupted, the metal housing of the load becomes under power as well. That’s a thing of the past but it was a part of our life those days…
I worked on a 3 phase oven a big big boy oven. It needed a neutral. It was 3 phase but worked as single phase. As each pair of elements. Was only on one pair at a time.
What was the voltage applied to the heating elements? 416 or 240 volts? Sometimes the elements are 416 single phase and multiples of three, and the controls are rated at 240 volts. It could be either way, just how they are connected in the equipment. Best wishes, Kevin
This isn't the first time I've seen this question recently. Kirchoff's law is the science. The confusion is only how to apply it! Multi-phase (or even the U.S. split phase) systems add some complexity, but the same law applies - the current in the conductors must sum to 0. Too bad your simple clamp meter discards the sign. It is much easier when the direction is indicated by the sign on the quantity.
At 5:21 , but if you remove neutral, the circuit would be incomplete and no current would flow , especially when you have a faulty current protection installed.
When you study the history of electricity outlets plugs first it was two basically hot and neutral current flows both ways then due to electrocution shocks TVs radios your other appliances the two outlet had a wide and thin blade plug so the wide blade was neutral thin blade was hot. This specially helped in grounding chassis on radios and TVs. But because of the human factor they came out with the plug with the third terminal round called the ground this was great for grounding washing machines and electric motors the second plug design was great for ground chassis on TVs radios sewing machines mixers you name it it was a big improvement. Unless you're ground is tied into neutral at the main panel it's of no use to save anybody's life from electrocution.
Correct statement up to the point of a GFCI breaker installed in the circuits. They require no ground to operate and protect life from shocks or electrocutions.
@@KevinCoop1 it can't operate on 3 phase (1 phase) sharing the same neutral because live and neutral wire doesn't always equal on load therefore it will 'tripping'. CMIIW
Any imbalance on a multi wire circuit will show up as neutral load. Example: single phase 120/240 feeder or multi wire branch circuit. Phase A current 5 amps, phase B current 8 amps, neutral current would be 3 amps. If that was covered, sorry, I missed it.
Couple years ago I used 3 phase for powering a few dosens of single phase crypto mining RIG's... At some point I check the cable and it was so hot. Then I did same as you mentioned to balance the phases and voila cable isn't hot anymore :)
Yo, this is magic stuff 😍 Iam just rolling into big buildings with 3 phase ac and hi power pumps and motors I'll stick to this channel Fwy, I imagined that it has to do with the 3 phase, if you would add up the 3 loads trough the neutral it should be way bigger than 2.5 2 waves can cancel each other out. Dad was a guitarist 😅
The key word is a perfectly balanced system! If any of the loads brings asymmetry to the system neutral turns into leverage conductor. The easiest way to explain it is by using rotating vectors. In perfectly balanced system 120° between each phase enables the current to flow and the neutral is a superfluous component. If you can draw three sine waves with 120° shift between them it becomes self explanatory why the current flows without the neutral conductor.
A question I would like to ask to follow up on your video. On my home immersion heater that needed replacing the neutral wire became over heated where the insulation had melted at the terminal. I have also seen this same thing on an electrical shower and oven. Why does the neutral wire show signs of burning but not the live wire?
The only reason that the wire would overheat is likely to be increased resistance at the connection terminal, resulting in heat generation. The current in the supply wire and neutral wire would be the same value, so if the supply wire is not overheated the supply terminal would be low or virtually y no resistance.
@@alanwhitfield1907 I agree but it always seems to be the neutral wire that gets charred, not the live wire, so there must be some thing more to this. I have seen accounts in other forums about this situation of the neutral wiring showing signs of over heating and not the live as well so it is a bit of a puzzle as to find some sort of explanation why this happening.
@@mightymax232 In all the cases i've seen, and theres a lot, the neutral burns because its loose. I have no idea why electricians cannot tighten them the same as lives.
This can also happen when the 3 live wires are not connected to 3 different phases. Then loads on the same phase combine, and because they have twice the copper for L than N...
The 3Ø RCD is smart, if the L1 (5A) L2 (5A) L3 (5A), RCD KNOW the neutral must be zero. If L1 (5A) L2 (0A) L3 (0A), RCD KNOW the neutral must be 5A. -------- And 1Ø RCD (2P RCD) work as curren Of the Phase = curren of neutral -------- But do you know this video all Load same Power Factor so in reality of there three loaded same current but they not same Power Factor the neutral will be have current
Probably worth noting that in an unbalanced 3 phase system the current on neutral will never be more than the maximum current that is in any one phase, so even if you can't manage to balance your loads the neutral conductor doesn't have to have a higher capacity than any of the hots.
More electricians' questions answered 👉 ua-cam.com/play/PLmWOIPxaBWH7XMcW07S7CTQM9G-M1GHzc.html
Actually, technically No. Current doesn't flow in a conductor, it flows around the conductor, or so i was taught at trade school. Current in the neutral must equal the current in the active, how else does an ELCB work!
Try a star connected 3 ph motor
Don't know how UK electric works other than that you lot use 50 Hz instead of 60 Hz, but in the US you can't have 3 different devices share 1 neutral with 3 phase power. It used to be allowed, but the NEC was changed in 2014 I think. It's a lot of fun trying to fish 2 new neutrals in the old conduit to upgrade old buildings. (not)
For fear of undiscovered nicks/shorts when the power is turned back on, oftentimes we just hook new wire with additional neutrals to the old, and use the old for the pull line to install the new and then recycle the old.
A couple of gotchas with 3 phase neutral: 1) If there is a fault the absence of a neutral connection can allow overvoltage on the phase conductors without tripping breakers and the risk of shock or fire in any connected loads and 2) someone might connect a 3 phase + neutral appliance like an industrial heater to single phase power, joining all 3 phases together and tripleing the current in the neutral. Best case the neutral wire burns out, worst case the building burns to the ground.
@@markhill9275 OMG OMG OMG....Current doesn't flow in a conductor, it flows around the conductor,???? matter, atoms, electrons, neutrons... learn your lessons again
I just discovered this channel and I love it. I´m a Electrical and Computer Engineering student and love all things related to power grids and house installations, your explanations are more on a "practical" rather than theoretical approach and I just find it much easier to comprehend. Amazing work!
Cheers Hugo
An outstanding presentation. I am a retired electrician and most of my work was done on 480 VAC three phase control circuits. I worked with maintaining large 50+ horsepower 2-speed motors and things like that. I also worked with DC traction elevator motors. I found it to be very enjoyable work. Your presentation is spot on!! I just subscribed so I will be seeing more of you. Cheers!
That's so clear now ! 😀 Also, explains why the neutral doesn't have a bigger cross section cable!
For anyone having trouble envisioning this, it's a bit easier if you start with something like American (two phase) house wiring, which comes in from the pole transformer as 240V, but with a center-tapped neutral wire. That means that neutral to either live conductor is 120V, so you basically have two 120V circuits, but each one is 180 degrees out of phase with the other (and typically half of the house circuits will be wired to one side and the other half to the other side).
Because of this, if you need more than 120V for some appliances (such as many stoves, water heaters, EV chargers, etc), you can just connect them across the two different "live" wires to get total of 240V instead. In that case, you don't need the neutral wire, because all of the current going in on one side is balanced by the (exactly opposite) phase on the other wire going out.
But it also means that on the neutral line going back to the pole, there may or may not be a lot of current, depending on how well the loads on the different house circuits are balanced. If you've got the same amount of stuff going on one half as on the other half, then all of the current will go "in" from live A to neutral, then from neutral to live B and back out again, and there will be no net current on the neutral line. However, if there's more load on the A side than the B side (or vice-versa), then all of that excess needs to go back out the neutral instead.
Thanks for this explanation on the US voltage supply.
FFS! If you have trouble envisioning it then go back and re do your entire electrical training!
It's that basic a question. And if you don't know the answer to it, you shouldn't be anywhere near mains electrical installations, even if you are "qualified". Because for you not to know the answer means that: 1. You have forgotten your basic electrical education, and 2. That you don't really understand electricity.
180deg across the phases. You sure about that?
@@greenpedal370 Yes, he is quite correct about their being 180 degree phase shift between the two lines in the US split phase system.
If you know enough about sine waves and electricity, you will realise that 180 degrees is the only way that is possible.
If you think he is wrong because you think it should be 120 degrees, then that is certainly incorrect. 120 degrees phase shift between phase conductors only occurs in 3 phase systems. And that is because they physically position coils around in the generator at 120 degrees around the rotor.
In the US split phase system, the phase signals that are distributed to consumers do not originate from the power station and generator, they are produced by the down stream distribution former and is a result of how the secondary windings are connected. It's very different to 3 phase.
wow that explanation made my brain hurt
This could also be drawn up as vectors. The phases are 120 degrees out of phase, a balanced load drawn as vectors would also show 0amps, and an unbalanced load would result in a vector length equal to the amps drawn in the neutral. That's how I learned it and understood it best in school, but this was also a great explanation! Nice and simple, keep it up! :)
I was trying to explain this to a cocky technician, who was 15 years senior to me. He was having none of it. I designed a control panel with a 3phase 2.5mmsq supply. There was a 16A single phase breaker on each live. His argument was that this arrangement would put 3x 16A=48A of load on the Neutral (2.5mmsq) wire. To prove he was right he even rang his mate, who was a lead in Intel, and they both were in agreement on this. Good guy though.
The neutral wire is the return path for unbalanced current in an AC circuit. It is not additive, it is subtractive.
Put an amp clamp on the neutral wire of a nominal load, and you’ll even see that the current on the neutral will be equal to the current on the line wire.
Doesn't wire size limit current flow ??
@@PORTEnSious yes wire size affects current flow as smaller wires can introduce greater resistant. But this is effectively in series so affects current through the whole of that circuit. Same way an appliance would affect current. V=I/R
But that doesn't really affect the topic in the video. As what ever current passes still follows the rules they described.
Hope that helps
To be fair if it was the same phase they'd have been right.
I think some brains just don't like coping with multiple phases.
You'd hope better from an old boy though. 😁 They've had AC since Tesla lol
@@PORTEnSious Wire size doesn’t limit current flow, but depending on the size of the load vs. the undersized wire, what will happen is the wire will not be able to dissipate the heat generated quickly enough, and will cause rapid deterioration of the conductor insulation. Also what can happen is the the wire itself can melt, most likely at the point of termination closest to the load.
A real life example would be a water heater that pulls 23 amps and is being fed from a 30A breaker @ 240V, but instead of using #10 AWG copper wire (which is rated for 30A using the 60°C in the NEC ampacity table 310.16 for residential applications). For the sake of this example, the installer uses #14 AWG copper for this installation which using the 60°C table of NEC Art.310.16, is rated for 15A maximum.
In this situation, you have 23A running through wire that is rated for 15A maximum. In this install, you would definitely find overheating, burnt insulation, damage at the breaker and at the water heater disconnect switch, or directly at the water heater itself.
One thing I forgot to mention is the ampacities mentioned are maximums for periods of time 3 hours or less. There are specific rules in the NEC I don’t have time to mention, but generally if a load is intended to be ran for 3 hours or more at any given time, it is not supposed to exceed 80% of the breaker capacity. For example, if a shop heater is rated to draw 24A, the breaker MUST be rated for 30A (30X.80=24A).
It's good to b reminded of stuff like this, especially after not having to think about it in a long time.
I challenge you to actually disconnect the neutrals with running equipment 🙂 Actually that would be a *really* bad idea. Happened at work once in the distribution board (faulty installation, took a couple of years to fail after the building was constructed). The insurance claim was I believe in seven figures and we were super lucky the building was not burnt down. Helped that the fire station was just across the road and they responded in under 90 seconds.
Used to do this on a similar experiment for my learners...
@@efixx For those that don't realize no neutral and all the lives float to 415V AC. The fire was started when the 400V rated capacitor in the power supply of a PC decided that being at 580V (415*sqrt(2)) was not good and flames came out the back of the PC (the slowmo guys have some nice footage of capacitors giving way), and set alight to the noticeboard behind (this is why the mains smoothing capacitor in a SMPS should be rated for 600V). The reason for the really high insurance claim was this was a biosciences lab and at lot of the very expensive equipment didn't take kindly to the 415V AC feed to them.
If it was unbalanced, the current would be present at the end of the disconnected Neutral. The equipment would look dead, right?
If you had just one heater and nothing else there would be no current flowing. If you had two heaters each 80 ohm (720 W) you would have 415 V over 160 ohm. That is 2.6 A and 1080 W (540 W each). That is if you have three identical resistors on a star connection with the neutral is connecting one reduces power by a third and two by 2/3. If you do not have a neutral then disconnecting one reduces power by 50% and two by 100%.
The real problem is that if you have some other loads in parallel like an incandescent bulb with 960 ohm. If it if gets in series with the 80 ohm heater at 415 V it gets 383 volts, i.e. it gets 2.5 x the power and will not last long.
If you disconnect the neutral upstream from the main panel then the voltage in it gets to the earth wire.
Had the neutral at the substation vanish with thieves, and the phases started to diverge on all the houses. Had the UPS start to warn about overvoltage, so measured mains at 270VAC. Immediately turned off all loads, and turned off the mains to the entire home as well, then went to the meter room and checked phase voltages. One was at 270VAC, one was around 230VAC, and the third was around 170VAC. Turned off the entire building, and got on the phone to the metro about a loss of neutral at the substation. Took them most of a day to fix it up, and they came back the next night to do it again, so they put up the steel doors instead of the wood, and welded all the cable access covers on, that they used to strip the SWA feeder cables leading to the street.
Nice video
Funfact
In Norway we have been running our mains network for 100 yrs with no neutral! Neutral is not absolutely needed. With no neutral and the loads in a dela konfiguration, that is all loads are connected between live 230V wires, the return currents ‘fines its way’ via the other wires. After 1995 all new houses in new areas are connected via 3-phase 230/400V TN networks, now with a neutral wire.
Yeah, I did learn this back when doing my C&G part 1, 2, 3.
It was really nice to see it all again in video format. I think we did it all in formulas back then.
My father taught me 3 phase theory 42 years ago. I never needed it but I see I still remember it correctly.
This is spot on . I think most people missed the fact that , even though you don’t need neutral , and depending on what you are running , and in this case 3 units 1 phase heater: it is safer to run a neutral at 1/3rd the max amp capacity , in this case and if in the event if one of the 1st phase heater encounters problems .
It would appear from the video that you need the neutral to be the same size as the phase conductors, as if one heater fails you need to be able to carry the full rated current of the phase conductor.
Well if you had no neutral and then disconnected one of the heaters the power would be reduced by half. With a neutral it will be reduced by a third.
This is exactly what I was wondering for a while now so thank you for explaining. I knew three phase motors didn't need the neutral because it was a balanced load but for some reason it never occurred to me that heaters would also work the same for some odd reason. Clever stuff.
Interesting demo. Will be valuable for all those domestic sparks that never get involved with three phase systems. Came across a large lighting circuit like this some time ago, gave me a bit of a head scratch till I realised that the neutral current will never exceed the current of one phase
Those domestic sparks that have only undertaken the domestic installation courses are not allowed to do 3 phase work (in that they are not allowed to do industrial installations).
And if people are qualified to do industrial electrical installations then they have been trained in 3 phase and should not need this video.
You woke up on the wrong side of the bed Dean? The video could be helpful for people who are in the process of qualifying for carrying out industrial installation work? 🤷
@@efixx quite agree there are plenty of time served industrial engineers that I know that would have to head scratch about this one
@@deang5622 in many parts of the world its normal to have 3 phase power in your home, even in apartments...
Do you mean "domestic spark from UK" only. All other domestic sparks around the UK (and commonwealth and U.S.A. ) use three phase connection to every house/garage/shed/fabric hall since Siemens & Halske around 1880 use 3phase AC and build the generators around the world!
Mind blown, but it all made total sense when you showed the wave form graph 👍
That's the reason the 400V continuous flow water heaters with 22 or 24kW, that are popular here in Germany for electric water heating for showers, don't require a neutral at all. In most cases we still install a five core cable. The five core NYM-J is only 1€ per meter more expensive than the four core one. Neutral isn't connected of course, but still available if it would be required in the future.
It’s a really good idea to pull the neutral always for future use, here in Finland it used to be acceptable to wire 3-phase sockets with no neutral, if they were intended for a large machine, it’s really fun when you rock up with a portable distribution board to only find that they left out the neutral. And it’s no fun either to have to install transformers for 400/230 just to get some new-fangled boiler with a control board that needs a neutral working. :)
@@sstorholm Or you install another motor, some require a neutral just to start, and while running it's disconnected.
@@Marcel_Germann What sort of abomination of a 3-phase motor requires a neutral to start?
@@sstorholm Not the motor itself, but eventually the electronics that regulate the speed of the motor. And maybe contactors if you want to reverse the direction of rotation.
And also possible, the future replacement requires for other reasons 230V in addition to 400V. Unlikely in industrial applications, but not unthinkable, and in domestic applications this can always happen. I remember my grandparents had a Perilex socket outlet (three-phase socket outlet )in their bathroom for the washing machine. The plug always "wandered" from the old to the new washing machine because it was the old rare 25A version.
@@sstorholmThe motor does not, but the control circuit may. Many EVs that insist on seeing a Neutral. A 1-phase Renault ZOE wil not charge unless one of the wires are a true Neutral and you need a 230/230V transformer with one of the secondary wires connected to ground to charge your car!
1:47 - lovely explanation of a DC circuit 😉
But the point still stands.
I knew this BUT you actually found a way to test and teach the theory. GREAT
JR
Many moons ago I was working in a computer factory (not as electrician :) ) when a cloud of acrid smoke tripped the fire alarms. Turns out the busbar chamber had a reduced size neutral, as the load was considered pretty well balanced. Ad Hoc alterations had seriously unbalanced the system and the neutral was glowing red hot with all it's PVC insulation burnt off! Turned off and fixed, with half a day's production lost, but could have had much more serious consequences.
The neutral over heated due to harmonics. Most times it is the 3 rd harmonic. It is a result of having loads that are non linear to current. That is variable frequency drives, computers, discharge lighting etc.
Thanks for the current measurement on the neutral with the two loads on L1 and L2. Both because it's not intuitive, and will force me to interpret the KCL and the desmos graph on my own as an "exercise for the reader". Where in the circuit are the neutrals of each of the individual phases physically connected? Within each of the outlets on that piece of plywood? The diagram at 5:36 shows the conceptual drawing; but where is are the physical connections of that neutral in the Y-config?
Always remember a site we took over from a previous company. They told the customer that all the 3 phase circuits had no neutrals and they all needed rewiring… just showed lack of knowledge on the subject.
Maybe more should be taught about things like this before people are let out on the wide world 😅
Neutral in a 3phase is generally found if the item has other elements eg control panels and other single phase components with in the 3phase item.
Great video guys!
He, he. Norway has been running 3-phase systems with no neutral for 100 yrs. All appliances are connected in delta style between live 230V wires.
Your video on your “Joe Robinson” channel on this same subject (a few years ago) was the moment the penny dropped for me! Very well explained Joe & @efixx👏
So when you had two heaters connected and measured the current on the neutral, it wasn't the same as L1 + L2 because it was partially mitigated by the opposing phases, but not completely as it was when you activated the third heater? - fascinating.
I've come to the conclusion that I am 'Electro-blind' !!! I love videos like this one and it is extremely well presented but I just can't get to grips with the physics of electricity lol. Keep up the good work and I'll just be happy I can change a 3 pin plug!
I would clarify slightly in your eater example, if you disconnected the 3 individual neutrals all 3 heaters would switch off but disconnecting the common point they would run in a star configuration. I know most viewers will know thats whats happening but just for clarities sake.
it would be good to see a video on that 👍
@@brianhewitt8618 star points are an interesting thing as is generator earthing which is a related subject. Not sure if efixx will cover them but maybe sparkyninja?
Great video and practical example of some basic electrodynamics, much appreciated
Hello, I just looked up this information and found your channel.
My dad is an (old time, retired) electrician and has taught me to do basic electric work.
I replaced a ceiling outlet (lighting) and instead of turning off the circuit, I just turned off the outlet as it's and old house and it's supposed to only have 2 connections (phase + neutral, no earthing) in most places. Turning off the phase should do the trick, and even if there is some leakage, it should only tingle. I verified everything with a basic "glow lamp" style seeker. No phases. And then verified with a multimeter - No current flow from L1 to Neutral.
However, I noticed the neutral had 2 wires attached. That was peculiar,but I thought it might just be sharing a neutral with some other light or WTF knows? It shouldn't be an issue.
When I disconnected the L1 from the ceiling outlet = no issue.
When I disconnected the neutrals, small spark and the lighting on the walls in that area of the living room (supplied by wall outlets) turned off.
Interesting. I shat my pants, stepped down from the ladder, took a moment to check myself, wondered why the RCD didn't trip (obivously it only sparked, didn't touch me in hindsight) and then turned off the entire house main feed. I'm not messing around anymore when neutrals and phases are mixed around everywhere.
Anyway, I told my dad and he refused the possibility of electricity in a neutral. I told him electricity is defined as a difference in charge, and there should be current flowing return in the neutral.
Now I understand it better, and I'll show him this video.
(Also, I'm the EU with a proper RCD and I use VDE tools with the 1-hand-behind-the-back principle when doing semi-stupid shit like this. Worst case is going to be a zap until the 30ma RCD cuts out)
Great explanation Joe.
Cheers Sergio!
Which is why years ago we used to install 31/2 core cables as supply cable with a reduced neutral when the single phase loads were relatively small
I received my new TIS voltage indicator today thank you eFIXX. It’s a great bit of kit , very much appreciated.
Great to hear!
You are absolutely amazing! I wish ( and I sincerely mean this) I had this tutorial video when I was doing my A levels!
It's simple. The 3 phasers are vector quantities and therefore add up to a resultant vector in the neutral depending on the magnitude and phase displacement. Electricians were taught this as part of their apprenticeship in my day...
Very interesting and well explained. However, if the incoming neutral becomes disconnected as I have experienced at a heritage railway, where the unbalanced loads caused serious problems with some devices burning out and other loads suffering low voltage. There seems to be no protection against such a problem and the supply company sometimes won't admit there is a fault.
Loss of the neutral is a serious issue. In single phase it does not give strange voltages but you'll get the full voltage at the equipment cases.
Great demonstration. Thanks. I know it but it is nice to hear/see it again.
Apprentice here. Excellent video, thank you. Only problem I see here is that, most (Yank) electricians have no idea what the sine waves represent, on the X & Y coordinates. It’s just a bunch of squiggly lines. It would be helpful if you clarified it, more than briefly mentioning that it’s current (w/respect to time) so viewers can fully grasp what’s going on in the graph.
How do you know most “Yanks” do not know what sine waves represent? Is it because you watch videos of people that say, “I’m not an electrician, so don’t do what I do” and show them working on 120/240 volt single phase electric system?
Great video. Well done. But it is clouding up the subject a bit. Of course, using three phase for single phase devices happens all the time, but single phase devices use one two hot lines. 120V and 277V devices use one hot line and neutral. 208V and 240V could be either one hot line and neutral or two hot lines and 480V is always two hot lines (all examples are single phase). I would like to see this using a single-phase supply, L1 of the 240V single phase supply wired to all three heaters in parallel, then check the neutral amps as each heater gets energized. A previous comment said the standard residential supply is two phase because of the two hot lines. That is wrong. The standard residential supply is 240 Volt, Single Phase. Best Wishes. Hope you keep up the good work.
Thanks, this is beautifully explained and exactly the information I needed for my 3ph to 1ph (3 outlet) extension cord.
It is true that passive loads, resistive or inductive will balance out and there will be no current in the neutral. However with loads where the power factor is less than 1 and the shape of the current trace is wildly different than the shape of the voltage trace such as most switch mode power supplies without active power factor correction, you can in fact have a greater current on the neutral than any of the 3 phases in the circuit. Something to consider for installations where the bulk of the power goes through switch mode power supplies such as variable frequency motor drives or datacentres. But active power factor correction is getting more common in such power supplies nowadays so their current draw is becoming more sinusoidal instead of only drawing current at the very peaks of the voltage which when the load is large turns the sine wave into more of a square wave.
very nice demonstration of Kirchhoff's current Law
Hats off to you sir ... really thank you for the simplicity ..
This video just blew my mind. Great information and really clearly presented.
Very well explained from average person point of view.
THANK YOU GUYS
A good demonstration for non Sparky’s to understand 👍
I really resinate with your method of Instruction. a big thank you!
One way of thinking about this is that the neutral current is the total phase imbalance. One phase loaded(= 1kw imbalance). 2 phases loaded (= 1 phase = 1kw imbalance). 3 phases equally loaded - no imbalance.
You can think it as an equilateral triangle, When you go one side you are one side away from the start, then after the second it is the same but the third side gets you where you started.
Mist cleared for me . Thank you
Wow, I’ve been looking for this. Thank you
That's an excellent explanation .being a growatt service engineer, I was wondering why the ongrid inverter works fine without neutral.
Well said very easy to understand when you visualize it this way
Fun to watch, when you already know why and he explains it well :)
I learned all this when I was an apprentice 60 years ago.
Now that I found very interesting and informative thank you Joe excellent explanation.
Fantastic video as always Joe 👍❤️
If your circuits are not balanced in the breaker box, you can get current flowing on the neutral line. Also, if the protective covering on the wires feeding your breaker box crystalize, you can also generate current flowing on the neutral line.
You can argue with me all you want, but I learned this through experience when we installed a minicomputer in our newly renovated building. The computer was blowing boards every month, so we put a line analyzer on the system and discovered current on the neutral line. Apparently, computers do not like current on that line. Upon diagnosing the problem, we discovered what I mentioned above. Once we fixed those two problems, the current was no longer found on the neutral line.
in a sense, the protective covering being crystalized creates more resistance big enough that it creates an imbalanced load. In real world application tho, no circuit is ever balanced. A balanced load is more of a theoretical circuit .
do the same with 3 x non-PFC power supplies (like your laptop's PSU) Even when all lines are balanced, you shall see a current in the neutral. The 3rd current harmonics are summed up in the neutral
The heaters are rated at 230vac input. Line to line voltage is 400vac. Square root of 3 (phase system) is 1.732 and is always applied to power calculations. 400vac over 1.732 is 230vac, which would be measured between any line and the common point. 3 phase resistive load; Ib = P/Vx1.732
Question from a layman. If current is flowing thru the neutral circuit why can't you recycle or re-use it, & does it "return" to the supplier or could you feed it into a battery or transformer intercept without "consuming" any more celectricity ?
Well explained, but any electrician who does not know this should not be let loose with a screwdriver!
New people train to join the industry every year - knowledge is power.
Howdy. Yes.
If the load is a delta configuration no neutral is needed either. The currents need not be symmetrical.
It is defined that the neutral needs to be only half the phase cross section from 16mm2 upwards. That is true in most cases. However, powerful solid state frequency converters may generate very strong harmonics. Some harmonics cancel each other but some get added in the neutral. The neutral rms may be way higher that what half a cross section can carry. With converters the neutral should be the same as the phase at least to 25mm2 copper. Preferrably to 35mm2 copper even.
In modern converters efforts have been made to decrease the neutral currents. Always check the specs for what cross section is needed for the neutral.
Regards.
Why was the current the same on the neutral when two heaters were hooked up. If you explained that I missed it. Also how does current flow without the neutral connected. I know 220 doesn't have a neutral but unless Im mistaken each leg reverses acting like a neutral.
Hi what is be the most likely cause of over-voltage in a 3 phase system? One of the phase was found with voltage of 385V and it tripped the CBs and caused damage to equipment that were connected to the phase.
Very nice practically explained
Excellent presentation
Thanks
If you're interested in electricity kirchoffs law is pretty interesting as is thevanins theory, not super heavy in maths but worth a look in my opinion
In my 3p installation (French farm house), I am required to keep the three single phases as balanced as possible. If I don't keep them an average over the day of no more than 30% from balanced, I am charged for the imbalance. Actually the power company use a average of averages over a rolling ninety days with each day being the final day of the window - a rolling window of usage, if you will. It's a very fair way of calculating poor usage of multi-phase mains.
In this case, a current sensor on the neutral is being used to discover the extent of any imbalance rather than having a meter on each phase. In reality, I have access to this data, including usage on each phase using a IoT meter I built myself which contains four current sensors attached to an Arduino with a wifi module to send the details in real-time to my own metering software as an MQTT stream. I then create a graph using Grafana this to show when imbalances occur and can adjust the loads on each phase accordingly without having to guess which is underused. Not too long ago such metering hardware and software would have cost a fortune. Now it is possible to do it for a few quid.
What a rip off! But I’m thinking it would be hard to have a 30% average imbalance over 90 days once you fix the condition once.
Hi, great video just have one question on the neutral currents .
In a 3-phase load I think i understand the concept of how the appliance uses the other 2 phases as a return path as opposed to the neutral.
However in a situation such as in this video where 3 separate single phase loads are connected. How can the appliances use L2 or L3 as a return path? If the neutral were to be disconnected then surely there would only be 1 line conductor to each appliance? How would the appliances continue to operate if the other phases are not present at the appliance to act as a return path?
It seems like I’m missing something here but I’m just scratching my head at the idea of an appliance operating with only one single conductor at point of connection..
hoping you guys can help me on this one hope I’ve made the question understandable!
you're probably thinking that all 3 currents at any given moment are coming out the source. This is impossible in 3 phase. What is really happening is, at one moment in time, only TWO phases have current going out, and combine (vectorially) to return on the 3rd phase. For example, at one moment, A and B going out and combine to return on C. Next moment, A and C going out, and combine to return on B. Then next moment, B and C are going out and combine to return on A. And repeats. Of course this is in the context of a balanced circuit. Hope this clear things up
PME systems (TN-C-S) effectively remove (minimise is more accurate) any current from the Neutral in the DNO's supply side network but obviously that is not the case in the customer's Consumer Unit
With each customer on a TN-C-S system the current from the Line to the Neutral is the same.
However, over a large number of such customers on the three separate "Phases" the total/residual current on the "Neutral" conductor will be quite small - hopefully, zero.
🤯 Wow, that was explained very well. 👍🏽
Different when it comes to Harmonic distortion, particularly the 3rd harmonic. These harmonics are the result of nonlinear loads that convert AC line voltage to DC, i.e. frequency converters, PCs etc. This causes a much higher current to flow in the neutral even in a balanced designed system, thus needing to install Active or passive harmonic filters to take them out and balance the load again or simply oversizing the neutral conductor to exceed the phase wiring by 50% to accommodate the higher current
Yes, in forward phase theatrical lighting systems, neutral over-current can be a big problem! Basically, at certain settings, the dimmers may all be drawing current near the end of the half-wave so there is no cancellation. The result is that the neutral conductor is carrying the highest current load. In the US, NEC requires such systems to oversize the neutral conductor. As harmonic filters would trow of the Zero-Cross Detectors in the dimmers, oversize is the only solution.
In the US, high harmonic loads are required to have the neutrals doubled in size to handle higher amperes on the neutrals. Special transformers are also made. Best wishes, Kevin
Brilliant explanation
Thanks
My predictions for that experiment were:
- Current on neutral equal to current on live if one is turned on
- If two are on, current on neutral will be about halfway between one of them, and both added together
- If all three are on, no current on neutral
Now, I did watch the solution before writing this, so I know I got the second one wrong, but the idea was correct. Because both are on, there is an additional return path, and so less current needs to return through the neutral.
If all three are on, the only current you would expect on the neutral is the difference in consumption of the heaters. Since they are all very similar, you wouldn't expect very much. They are all on different phases, so there is always a return path through one of the other heaters.
...now, I am writing this after seeing the solution, but before the explanation... so let's see how wrong I got that, lol
pretty much exactly.
A new way of saying things :)
I remember doing this in college and it's totally unintuitive until you look at the circuit operation.
👍🏻
“The answer is Yes!”
The problem is when the neutral conductor of the load losses its connection with the neutral line of the power grid. I’m from Bulgaria. In the backward years (40-50 years ago) our power grid was 2-wire one - Line and Neutral only, without Ground wire. All loads with metal housing were “neutraled” instead of grounded because the power sockets were bridged to the neutral instead of separate ground wire. And there comes the problem - when the neutral conductor is interrupted, the metal housing of the load becomes under power as well. That’s a thing of the past but it was a part of our life those days…
Gray video and great explanation. Big thank you 👍🏼
Wonderful explanation . Thanks.
I worked on a 3 phase oven a big big boy oven. It needed a neutral. It was 3 phase but worked as single phase. As each pair of elements. Was only on one pair at a time.
What was the voltage applied to the heating elements? 416 or 240 volts? Sometimes the elements are 416 single phase and multiples of three, and the controls are rated at 240 volts. It could be either way, just how they are connected in the equipment. Best wishes, Kevin
@@KevinCoop1 Don't recall now just the way the contactors were wired up. Do think somewhere I have a photo of the front so I will look it up one day.
Ovens need a neutral as they can have numerous different power settings. Something like a sauna does not need as it is either on or off.
Brilliantly explained as usual thanks 👍👍
I’m not a sparky yet I understood it. Thank you.
This isn't the first time I've seen this question recently. Kirchoff's law is the science. The confusion is only how to apply it! Multi-phase (or even the U.S. split phase) systems add some complexity, but the same law applies - the current in the conductors must sum to 0. Too bad your simple clamp meter discards the sign. It is much easier when the direction is indicated by the sign on the quantity.
Finaly an answer to a question
so thats why the nutral does not have to be thicker mm3?
Very good explanation. Thanks
At 5:21 , but if you remove neutral, the circuit would be incomplete and no current would flow , especially when you have a faulty current protection installed.
If you've got a balanced three phase load you can lose the neutral and the circuit will work fine. 😃
@@efixx is that legal? the electrical meter won't read the electrical consumption without neural, right ?
@@tom2010ad Are you serious? Of course the meter reads all the phases. If there is no current in the neutral how could removing it affect anything?.
When you study the history of electricity outlets plugs first it was two basically hot and neutral current flows both ways then due to electrocution shocks TVs radios your other appliances the two outlet had a wide and thin blade plug so the wide blade was neutral thin blade was hot. This specially helped in grounding chassis on radios and TVs. But because of the human factor they came out with the plug with the third terminal round called the ground this was great for grounding washing machines and electric motors the second plug design was great for ground chassis on TVs radios sewing machines mixers you name it it was a big improvement. Unless you're ground is tied into neutral at the main panel it's of no use to save anybody's life from electrocution.
Correct statement up to the point of a GFCI breaker installed in the circuits. They require no ground to operate and protect life from shocks or electrocutions.
@@KevinCoop1 it can't operate on 3 phase (1 phase) sharing the same neutral because live and neutral wire doesn't always equal on load therefore it will 'tripping'. CMIIW
Any imbalance on a multi wire circuit will show up as neutral load. Example: single phase 120/240 feeder or multi wire branch circuit. Phase A current 5 amps, phase B current 8 amps, neutral current would be 3 amps. If that was covered, sorry, I missed it.
The thing im curious about is, what would happen if you connected single phase a load after the star point neutral?
Nice video, very informative
Great Video, very helpful. Thank you guys!
Couple years ago I used 3 phase for powering a few dosens of single phase crypto mining RIG's... At some point I check the cable and it was so hot. Then I did same as you mentioned to balance the phases and voila cable isn't hot anymore :)
Very good explanation with examples. 👍👍👍👍👍
Correct me if I am wrong but don't both active and neutral go back to the generator and form the return.
Yo, this is magic stuff 😍
Iam just rolling into big buildings with 3 phase ac and hi power pumps and motors
I'll stick to this channel
Fwy, I imagined that it has to do with the 3 phase, if you would add up the 3 loads trough the neutral it should be way bigger than 2.5
2 waves can cancel each other out. Dad was a guitarist 😅
The key word is a perfectly balanced system! If any of the loads brings asymmetry to the system neutral turns into leverage conductor. The easiest way to explain it is by using rotating vectors. In perfectly balanced system 120° between each phase enables the current to flow and the neutral is a superfluous component. If you can draw three sine waves with 120° shift between them it becomes self explanatory why the current flows without the neutral conductor.
Interesting stuff...I was expecting "it depends on if it is fed from a Star or Delta transformer..." great explaination.
Thanks for the topic, effort & way explained.. Q: Why sometimes we find current flowing even thu breakers are off mode..
A question I would like to ask to follow up on your video. On my home immersion heater that needed replacing the neutral wire became over heated where the insulation had melted at the terminal. I have also seen this same thing on an electrical shower and oven. Why does the neutral wire show signs of burning but not the live wire?
The only reason that the wire would overheat is likely to be increased resistance at the connection terminal, resulting in heat generation. The current in the supply wire and neutral wire would be the same value, so if the supply wire is not overheated the supply terminal would be low or virtually y no resistance.
@@alanwhitfield1907 I agree but it always seems to be the neutral wire that gets charred, not the live wire, so there must be some thing more to this. I have seen accounts in other forums about this situation of the neutral wiring showing signs of over heating and not the live as well so it is a bit of a puzzle as to find some sort of explanation why this happening.
@@mightymax232 In all the cases i've seen, and theres a lot, the neutral burns because its loose. I have no idea why electricians cannot tighten them the same as lives.
This can also happen when the 3 live wires are not connected to 3 different phases. Then loads on the same phase combine, and because they have twice the copper for L than N...
1:23 hey I have that same multi meter in Green! Although that looks like it may have an extra button.
So how would an RCD work in a 3 phase installation work if there is a difference between the current on the line and neutral?
The 3Ø RCD is smart, if the L1 (5A) L2 (5A) L3 (5A), RCD KNOW the neutral must be zero.
If L1 (5A) L2 (0A) L3 (0A), RCD KNOW the neutral must be 5A.
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And 1Ø RCD (2P RCD) work as curren
Of the Phase = curren of neutral
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But do you know this video all Load same Power Factor so in reality of there three loaded same current but they not same Power Factor the neutral will be have current
Probably worth noting that in an unbalanced 3 phase system the current on neutral will never be more than the maximum current that is in any one phase, so even if you can't manage to balance your loads the neutral conductor doesn't have to have a higher capacity than any of the hots.