Neutral bar

Estiban · Apr 13, 2021

Hi
What’s the principle .
with a neutral not connected to the neutral bar will be 230v basically a line.
But when neutral is connected to neutral bar there is 0v.
Neutral and earth are connected further on with the same potential but I still don’t understand how the neutral bar and even the earth bar isn’t at 230v ?

Soi disant · Apr 13, 2021

Estiban said:
Hi
What’s the principle .
with a neutral not connected to the neutral bar will be 230v basically a line.

230V between N and what?

What makes you think there will be a potential difference of 230V between N and whatever-it-is?

Estiban said:
But when neutral is connected to neutral bar there is 0v.

0V between N and what?

Estiban said:
Neutral and earth are connected further on

Downstream of the cutout they'd better not be.

Estiban said:
I still don’t understand how the neutral bar and even the earth bar isn’t at 230v ?

230V between them and what?

Assuming (as seems reasonable), you're talking about the regular 230/400V public supply in the UK, the star point of the supply transformer is N and is tied to earth.

Each phase is 230V wrt that.

Not sure what it is you're asking/don't understand....

timhoward · Apr 14, 2021

I think he's saying that as a N conductor has potential of 230v if loose, then you connect it to a N bar, why isn't the N bar then at a 230v potential. And on TNCS systems as he correctly says the Earth is connected to the Neutral so in turn why isn't that at 230v potential.

The simple answer is that as per the diagrams above the N in the supply is connected to the mass of real earth so is held at a fixed potential of 0v.

For current to flow we need a potential difference; with a completed circuit we have a potential difference peaking at 230v to 0v half the time, and -230v to 0v the other half of the time.
When all connected normally current can flow, and the amount that flows depends on the resistance of the circuit load.
With N disconnected there is no completed circuit between two potential difference points, the N end of the circuit is "floating" so remains at 230v.

Soi disant · Apr 14, 2021

timhoward said:
I think he's saying that as a N conductor has potential of 230v if loose,

Sorry - when you say "loose", what do you mean?

And 230V wrt what?

timhoward said:
then you connect it to a N bar,

Before you do that, what makes it a N conductor?

timhoward said:
why isn't the N bar then at a 230v potential.

Why isn't it at 230V to what?

Why is is a "N bar"? What makes it so? What properties does it have?

timhoward said:
And on TNCS systems as he correctly says the Earth is connected to the Neutral so in turn why isn't that at 230v potential.

Why isn't that at 230v potential to what?

timhoward said:
The simple answer is that as per the diagrams above the N in the supply is connected to the mass of real earth so is held at a fixed potential of 0v.

Held at a fixed potential of 0v to what?

timhoward said:
For current to flow we need a potential difference; with a completed circuit we have a potential difference peaking at 230v to 0v half the time, and -230v to 0v the other half of the time.

325V, actually.

timhoward said:
With N disconnected there is no completed circuit between two potential difference points, the N end of the circuit is "floating" so remains at 230v.

Disconnected from what?

Why are you calling this disconnected thing neutral?

It remains at 230V to what?

ipf · Apr 14, 2021

Talking 'return'. A return cable has to be connected to 'Neutral' to become a neutral. If not, the circuit's incomplete. Testing whilst disconnected, it's in series with the live supply.

Soi disant · Apr 14, 2021

And it's not a neutral conductor.

ipf · Apr 14, 2021

Soi disant said:
And it's not a neutral conductor.

Too late for picking.....we know what he means.

Soi disant · Apr 14, 2021

Ah - this is the trouble. It's not being picky - understanding how circuits are completed, and how a potential difference has to be between two points which are in the same frame of reference, and what that PD is, and when, and why, is fundamental and crucial.

If you disconnected a circuit conductor from an MCB, would you still call it the line conductor? What would you call it if you connected it to the + terminal of a 12V car battery which wasn't connected to anything else?

westward10 · Apr 14, 2021

@Soi disant the OP is a trainee and you firing short sharp responses back to other people's posts is not going to help anyone.

DPG · Apr 14, 2021

Some people seem to enjoy being awkward. Give the guy a break, he's a trainee and all that will happen is he will get fed up of unhelpful answers and lead the forum.

timhoward · Apr 14, 2021

@Soi disant I know what you are getting at and agree the terminology is not exactly spot on but I think we’re going down rabbit holes a bit and we don’t want to scare the OP away.

timhoward · Apr 14, 2021

Soi disant said:
What would you call it if you connected it to the + terminal of a 12V car battery which wasn't connected to anything else?

It sounds rather like a Fiat?

Soi disant · Apr 14, 2021

westward10 said:
@Soi disant the OP is a trainee and you firing short sharp responses back to other people's posts is not going to help anyone.

Sorry - didn't mean it aggressively or anything - just trying to break it down into basic fragments, and to get people to think about them.....

I strongly suspect that the OP actually understands more than he thinks he does, or at least would understand more, if he thought about the things he already knows.

telectrix · Apr 14, 2021

@OP.basically, in normal service the 230V is dropped across the load/s. if you disconnect the neutral from the supply side, there is no current flow and hence no volt drop, sot the N is at a 230V potential. ohms law V=IR, where I =0, then VD =0.

Soi disant · Apr 14, 2021

telectrix said:
if you disconnect the neutral from the supply side, there is no current flow and hence no volt drop, sot the N is at a 230V potential.

No, it isn't. The supply neutral is still at a nominal 0V to earth, and the supply line is still at a nominal 230V to N & E.

What you have disconnected is no longer the neutral. It inherits its status as neutral by being connected to the neutral point in its frame of reference, i.e. the supply neutral. If you disconnect it from that it loses that status.

Most of the time that distinction doesn't matter, but it absolutely does when trying to understand that voltages are not singular, isolated things but are a difference in electrical potential between two points.

Neutral bar

Estiban

Soi disant

timhoward

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Soi disant

ipf

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Soi disant

ipf

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Soi disant

westward10

DPG

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timhoward

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timhoward

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Soi disant

telectrix

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Soi disant

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