Current flow in neutral but no voltage ?

[Rob678]

Having a challenge understanding the concept behind why when you measure across line and neutral (live circuit) using voltage indicators we have voltage reading of 230V single phase. If there is current flow in the neutral why is it termed as 0V ?
On that basis, second question - If I tested across Neutral and Earth, there is current flow down the neutral back to the transformer, why would the tester show 0V ?

 

[Avo Mk8]

Think of the basic generator you described at the beginning of your previous thread, except it is now generating 230V. You connect one wire to an earth stake and also to one connection of a light bulb. The other generator wire connects to the other bulb connection (call that 'live'). This somewhat mimics power coming into a house.
You are standing on the earth. You touch the wire that is connected to earth. Why would you get a shock?

This is what is happening on the 'live' wire - does this help?
(PS I may have confused things with a red line - that's just supposed to represent the zero volt axis of the 'live' waveform)

 

[Rob678]

Think of the basic generator you described at the beginning of your previous thread, except it is now generating 230V. You connect one wire to an earth stake and also to one connection of a light bulb. The other generator wire connects to the other bulb connection (call that 'live'). This somewhat mimics power coming into a house.
You are standing on the earth. You touch the wire that is connected to earth. Why would you get a shock?

This is what is happening on the 'live' wire - does this help?
(PS I may have confused things with a red line - that's just supposed to represent the zero volt axis of the 'live' waveform)
View attachment 112668

I think so. So the generator in a simple form has a large magnet in the middle rotating, creating a push pull (voltage) positive negative force.
Three phases leave the generator and end up at a step down transformer that steps it down to 230V. Up until this point no neutral is needed as the three phases balance each other out ?
Now,
At this point, in the centre of a star connection transformer we introduce a neutral. From a single phase we connect this to a property. As this property is single phase we need use a neutral which connects back to the neutral in the road which is connected back at the centre of the star connection.

What I am struggling to grasp still is why the electricity upto this transformer is alternating.
But then when it comes into the house only the line side is live.
Using the second diagram of the transformer I’m struggling to understand why if I grabbed hold of the neutral I wouldn’t get a shock as by an alternating current concept for half the time the current is flowing through this cable.

The only way I can make this make sense in my head at the moment is - If I’m holding the neutral. The current is attempting to flow through me through the ground and back to the transformer. And because the neutral is connected to the earth. I am effectively at the same potential difference to the ground i.e, if the neutral cable Im holding is either pushing or pulling the electrons, because I am connected to the ground, which is connected back to the neutral. There can be no push or pull effect because, back at the transformer neutral and ground will always be the same charge either positive or negative, so there is no electron flow.
I sort of think I have explained to myself my conundrum I initially posted but I’m posting this anyway to see if I can get some confirmation from you guys.

Thankyou in advance

 

[Avo Mk8]

What I am struggling to grasp still is why the electricity upto this transformer is alternating.
But then when it comes into the house only the line side is live.

I think you are getting confused between the voltage on a conductor, and current flowing through it, or the relative dangers thereof?

Using the second diagram of the transformer I’m struggling to understand why if I grabbed hold of the neutral I wouldn’t get a shock as by an alternating current concept for half the time the current is flowing through this cable.

It doesn't matter whether we talk about AC or DC. Your concern relates to what happens when you connect one side of the electricity supply to ground/ earth/ 0V/ and you.
With one side of the supply grounded (eg Neutral) there is a DC or AC voltage on the other supply wire (as illustrated by the sine wave I posted)
The fact there is current going through the neutral, many Amps or whatever, won't give you a shock. The neutral is at the same potential as you. Even if an AC supply, it's not alternating, it is at zero potential all the time (before considering the real world of resistance of cables and connections). It's the live wire that's wanging up and down in voltage, but not the neutral - it can't - it's tied to ground/0V!

The only way I can make this make sense in my head at the moment is - If I’m holding the neutral. The current is attempting to flow through me through the ground and back to the transformer. And because the neutral is connected to the earth. I am effectively at the same potential difference to the ground i.e, if the neutral cable Im holding is either pushing or pulling the electrons, because I am connected to the ground, which is connected back to the neutral.

Yes

There can be no push or pull effect because, back at the transformer neutral and ground will always be the same charge either positive or negative, so there is no electron flow.

The pushing and pulling of electrons is all about current. There will be/ can be current. You not getting a shock is all about voltage. There is no voltage on the Neutral.

I sort of think I have explained to myself my conundrum I initially posted but I’m posting this anyway to see if I can get some confirmation from you guys.

Thankyou in advance

We don't mind if you keep asking if you don't understand. And I'm sorry if my attempts to explain don't resonate with you - I'm sure someone will be along to help!

 

[Rob678]

I think you are getting confused between the voltage on a conductor, and current flowing through it, or the relative dangers thereof?

It doesn't matter whether we talk about AC or DC. Your concern relates to what happens when you connect one side of the electricity supply to ground/ earth/ 0V/ and you.
With one side of the supply grounded (eg Neutral) there is a DC or AC voltage on the other supply wire (as illustrated by the sine wave I posted)
The fact there is current going through the neutral, many Amps or whatever, won't give you a shock. The neutral is at the same potential as you. Even if an AC supply, it's not alternating, it is at zero potential all the time (before considering the real world of resistance of cables and connections). It's the live wire that's wanging up and down in voltage, but not the neutral - it can't - it's tied to ground/0V!

Yes

The pushing and pulling of electrons is all about current. There will be/ can be current. You not getting a shock is all about voltage. There is no voltage on the Neutral.

We don't mind if you keep asking if you don't understand. And I'm sorry if my attempts to explain don't resonate with you - I'm sure someone will be along to help!

Right I think Im getting there, so current flow is happening throughout. However in a simple analogy the pushing and pulling action (voltage) is only pushing and pulling on one side (The phase/ line conductor side). So current flows back and forth throughout the circuit from the generator through the transformers into a domestic dwelling/ installation and then all the way back.
Neutral and Earth are bonded/ linked together at the same point in the centre of the star connection transformer. So if I was to touch a neutral, (stay with this bit) I’ve almost got an imaginary cable attached to my feet which runs back underground to the transformer, but this is linked at the same point the neutral is linked at. This imaginary cable being a route through the earth. Because I’m creating a circuit that back at the transformer end isn’t linked at two seperate points/ opposite ends of the transformer there is no potential difference as there can be no push or pull effect of electrons. Therefore no electric shock.
Where as if I am touching the phase wire I am completing a circuit from the phase through the earth which attaches to the opposite end of the transformer winding.
Since the phase side is connected to the opposite end of the neutral/earth there is a potential difference and work can now be done. I.e. the electrons can move back and forth - therefore electric shock/ electron flow

 

[Avo Mk8]

Right I think Im getting there, so current flow is happening throughout. However in a simple analogy the pushing and pulling action (voltage) is only pushing and pulling on one side (The phase/ line conductor side).

Yes the voltage (tension) is only on the live side as it were. The pulling and pushing distance moved was the current. Both ends of the rope move the same. The current in L and N are the same.

So current flows back and forth throughout the circuit from the generator through the transformers into a domestic dwelling/ installation and then all the way back.

yes

Neutral and Earth are bonded/ linked together at the same point in the centre of the star connection transformer. So if I was to touch a neutral, (stay with this bit) I’ve almost got an imaginary cable attached to my feet which runs back underground to the transformer, but this is linked at the same point the neutral is linked at. This imaginary cable being a route through the earth.

Yes. The ground is a conductor, so your imaginary cable is 'real', but with some resistance (sorry thats probably a complication!)

Because I’m creating a circuit that back at the transformer end isn’t linked at two seperate points/ opposite ends of the transformer there is no potential difference as there can be no push or pull effect of electrons. Therefore no electric shock.

I think I follow, yes. I find it easier to think in terms of current flow - just call it current - rather than worrying about electrons pushing or pulling.

Where as if I am touching the phase wire I am completing a circuit from the phase through the earth which attaches to the opposite end of the transformer winding.
Since the phase side is connected to the opposite end of the neutral/earth there is a potential difference and work can now be done. I.e. the electrons can move back and forth - therefore electric shock/ electron flow

Yes

 

[Rob678]

Yes the voltage (tension) is only on the live side as it were. The pulling and pushing distance moved was the current. Both ends of the rope move the same. The current in L and N are the same.

yes

Yes. The ground is a conductor, so your imaginary cable is 'real', but with some resistance (sorry thats probably a complication!)

I think I follow, yes. I find it easier to think in terms of current flow - just call it current - rather than worrying about electrons pushing or pulling.

Yes

Thankyou very much for all the help, I’m sure there’s lots more to learn but I do feel like I understand the answer to the question I initially asked.
So that all being said the phase conductor comes from the transformer to the installation and the neutral goes back to the transformer to the centre.
Back at the transformer on the opposite side of the windings we have the side of the transformer which goes back to the generator. (Let’s keep it simple and say there is only generator - transformer - installation). On the generator side of the transformer or back at the generator. What is the determining factor as to why it’s the tips of the star connection where our phase wire connects that carry the voltage ?
I would have expected back at an AC generator for a single phase to be connected in the generator at 180 degrees ?
What I’m asking is back at the generator which side is our voltage being produced on to then attach to the phase cables ?

I feel the answer is because of the neutral introduction, or to do with the way delta and star are connected ?

 

[Rob678]

Just had a look at some animations of a star and delta connection. Think I was getting slightly confused.
Taking mention back to previous early comments. All the phases work together because they are balanced as they leave the generator and then I’m guessing on one side of the transformer we have a delta connection and on the other side is a star connection. In this portion is where we get our phase conductor at the top which gives us the voltage transfer ?

 

[Avo Mk8]

Just had a look at some animations of a star and delta connection. Think I was getting slightly confused.
Taking mention back to previous early comments. All the phases work together because they are balanced as they leave the generator and then I’m guessing on one side of the transformer we have a delta connection and on the other side is a star connection.

Firstly, power distribution is not my thing, I'm not the best person to advise.
Conceptually you summary is fine. All phases are typically held at about the same voltage, via an earthing transformer or similar at the generator. And as you say, the generator can provide a balanced feed to a delta to star transformer to step down the voltage and provide the star tap.

In this portion is where we get our phase conductor at the top which gives us the voltage.
But it’s we get from one side to the other Im not sure about. Is that correct ?

Not sure what your asking here, but at the star outputs of the transformer you have the three live phases (don't touch!), and their star neutral point that is connected to ground (can touch!). So you could feed three households, one from each phase, and a neutral return to each. And in the unlikely event all three households are using exactly the same amount of electricity, eg the same current, (a balanced load), that current will be flowing in the neutral wires back to the transformer, and where the neutrals all connect together, their currents sum to zero. So for balanced household loads, the star neutral point of the transformer wouldn't carry any current. Mind blown. Of course that's an idealised situation.

 

[Rob678]

Firstly, power distribution is not my thing, I'm not the best person to advise.
Conceptually you summary is fine. All phases are typically held at about the same voltage, via an earthing transformer or similar at the generator. And as you say, the generator can provide a balanced feed to a delta to star transformer to step down the voltage and provide the star tap.

Not sure what your asking here, but at the star outputs of the transformer you have the three live phases (don't touch!), and their star neutral point that is connected to ground (can touch!). So you could feed three households, one from each phase, and a neutral return to each. And in the unlikely event all three households are using exactly the same amount of electricity, eg the same current, (a balanced load), that current will be flowing in the neutral wires back to the transformer, and where the neutrals all connect together, their currents sum to zero. So for balanced household loads, the star neutral point of the transformer wouldn't carry any current. Mind blown. Of course that's an idealised situation.

Thankyou very much for your help truly. Dis regard that last section I was looking at a picture of delta and star connection diagrams and taking them far to literal. I drew a Y inside an equilateral triangle to look how it would work and did a bit more reading to see how the coils actually wind around next to each other to create the contacts.

I feel like I’m there or there abouts.
Lastly I gather at a generator the ends of the cables are connected together in a Delta fashion. Then if we follow these three cables all the way over the plyons through the system eventually we get to a transformer which steps it down. We have a star or Delta connection one side and star on the other. Then from the star supply side, our phases then feed say a road of houses, and each of these houses taps onto the neutral to allow for single phase ?
If this is correct Thankyou very much for the help over the weekend. I’ve Definatley got a lot more knowledge than I started with on Friday.

 

[Avo Mk8]

Then from the star supply side, our phases then feed say a road of houses, and each of these houses taps onto the neutral to allow for single phase ?

Absolutely. All get the neutral and a phase. Blocks of flats and commercial buildings tend to get all 3-phases (and the neutral obviously), phases shared out within the building to balance the load where practicable. My previous house actually had a 3-phase supply to the fuse head, but just a single phase was connected to the meter.

Best wishes for a future in Electrics. Keep the faith!

 

[Rob678]

Absolutely. All get the neutral and a phase. Blocks of flats and commercial buildings tend to get all 3-phases (and the neutral obviously), phases shared out within the building to balance the load where practicable. My previous house actually had a 3-phase supply to the fuse head, but just a single phase was connected to the meter.

Best wishes for a future in Electrics. Keep the faith!

Thanks again, I’m sure I’ll be back with many more questions