UK Why is neutral at 0 volts?

[LmarshallSparks]

I’m confused why neutral is at 0v (or close too) in certain situations!

TN-C-S system for this example, no borrowed neutrals or faults! A simple lighting circuit!

Now I can understand that when the circuit is open neutral would be at 0 volts due to it being connected to the earthing conductor and having no line to it! Now let’s say we closed that circuit (turned a light on), I can’t understand why the neutral wouldn’t become 230v

Now I understand most replies will say due to voltage being potential difference we need that difference! However what I can’t understand is now that circuit is closed why doesn’t one of two things happen

1) The neutral becomes 230v
2) The line becomes 0v

Is this due to the extremely high resistance of a bulb or appliance etc using that voltage up, meaning that very few volts remain by the time the current reaches the neutral so it takes the easy path back to the transformer and lacks the power to take any other direction?

Or am I going far too complicated! Is it simply potential difference! The transformer is pushing 230v down the line and the neutral is connected to earth so will always remain at 0v (or close too)

Appreciate any help on the matter!

 

[James]

the entire voltage drop in the circuit is across the load (light in this case) the other parts of the circuit are at zero ohms or close enough to that for there to be no volt drop.
if you were to disconnect the N then it would become live but the lamp would not come on.

 

[Yellowhammer]

Neutral has current but no voltage. Current entering a node must equal current leaving it. As above though voltage is dropped over the load.

If it wasn't, all the pipework in your house etc. would come live via the bonding conductors, this would not be ideal.

 

[brianmoooore]

The full voltage available (230V) distributes itself along the live supply wire, the load, and the neutral wire in proportion to their individual resistances.
For instance, if the live supply wire was 1 ohm, the load 8 ohms and the neutral 1 ohm, there would be 23 volts from end to end of the live wire, 184 volts across the load and 23 volts across the length of the neutral. There would be no current in the earth wire, so if you connected a meter between neutral and earth at the load end you would measure 23 volts, but 0 volts at the supply end, for a TNC-S supply.
In practice, the supply wire resistances will be much less than 1 ohm and the load resistance will be much higher than 8 ohms for a domestic lamp, but even than there will be a measurable voltage between neutral and earth at the lamp end.

 

[LmarshallSparks]

Neutral has current but no voltage. Current entering a node must equal current leaving it. As above though voltage is dropped over the load.

If it wasn't, all the pipework in your house etc. would come live via the bonding conductors, this would not be ideal.

So simply put, the voltage is lost via the load (lamp in this example) so a very small amount of voltage then takes the current back to the combined conductor via the natural?

 

[mainline]

Neutral has current but no voltage.

Current cannot exist without voltage.

 

[brianmoooore]

Current cannot exist without voltage.

Voltage difference, to be pedantic.

 

[James]

Voltage difference, to be pedantic.

Superconductors are an even more pedantic argument!

 

[mainline]

Voltage difference, to be pedantic.

Potential difference being even more pedantic.

Yes, you are correct in that you're being pedantic

 

[mainline]

Superconductors are an even more pedantic argument!

I don't think a length of, 6242y can be classed as a super conductor

​

 

[James]

Potential difference being even more pedantic.

Yes, you are correct in that you're being pedantic

Please explain,
I am failing to understand why potential and voltage are not the same thing.

 

[mainline]

Please explain,
I am failing to understand why potential and voltage are not the same thing.

I was being a bit pedantic but:

Both voltage and potential difference refer to the same concept of the electric potential energy per unit charge between two points in a circuit. However, the term "potential difference" places more emphasis on the difference in electric potential between the two points, while "voltage" is a more general term.

Voltage is the electromotive force, or the electric tension.
Potential difference is a measure of stored energy of any form.
Electric potential and voltage are related, but not the same thing:

 

[brianmoooore]

'Voltage' is just stating units for potential difference. Similar to 'pounds' and 'money'..

 

[HappyHippyDad]

the entire voltage drop in the circuit is across the load (light in this case) the other parts of the circuit are at zero ohms or close enough to that for there to be no volt drop.
if you were to disconnect the N then it would become live but the lamp would not come on.

Hi James,
This is something I have struggled with too.
Neutral is connected to earth so it is at zero (ish) volts to earth.
What happens at the light (for example), for the voltage to change from 230v to 0v?
I realise it is more than just what is happening at the light, as if you disconnect the neutral along the route back, then it too becomes 230V to earth. However, it might help to understand firstly why the voltage changes from 230V to 0v at the light?