Does Current Flow Through The Neutral Wire?

One of the most amazing things about three phase electricity is that in a perfectly balanced system a neutral wire isn't needed. In this video, Joe Robinson shows how the neutral current sums to zero when an equal load is connected to each phase.

This helps to explain why the neutral conductor in a three phase cable is the same size as the other phases and why some industrial sockets don't have a neutral connection.

This electricians Q&A follows from our review of the Variabox, from CEENORM, which is a flexible power distribution system for industrial electrical installations.

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00:00 Industrial Electrical Installations
00:42 Does current flow in the neutral conductor - yes & no?
00:50 Neutral current in a ingle phase circuit
02:00 Neutral currents in a Three Phase circuit
04:09 Lower than expected current?
05:08 No neutral current?
05:48 Why does this happen?
06:30 Electrical installations with no neutral
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#efixx #electricians #threephase

[hugobrites]

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!

[jozefdkois]

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.

[foogod]

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.

[flashesofblack]

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!

[MarkSaeys]

That's so clear now ! 😀 Also, explains why the neutral doesn't have a bigger cross section cable!

[christvedt]

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! :)

[kjellg]

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.

[jonathanbuzzard]

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.

[FirstDan]

It's good to b reminded of stuff like this, especially after not having to think about it in a long time.

[anthonyschofield]

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

[Marcel_Germann]

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.

[tonywebb]

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.

[davidg]

Thanks, this is beautifully explained and exactly the information I needed for my 3ph to 1ph (3 outlet) extension cord.

[TigerP]

My father taught me 3 phase theory 42 years ago. I never needed it but I see I still remember it correctly.

[DesperateDan]

Mind blown, but it all made total sense when you showed the wave form graph 👍

[Savagetechie]

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.

[johnwarwick]

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

[TimGauntlett]

1:47 - lovely explanation of a DC circuit 😉
But the point still stands.

[MalaysiaBarista]

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 .

[robertpucovsky]

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.