Neutral bar

[Estiban]

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]

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?

But when neutral is connected to neutral bar there is 0v.

0V between N and what?

Neutral and earth are connected further on

Downstream of the cutout they'd better not be.

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]

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]

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?

then you connect it to a N bar,

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

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?

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?

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?

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.

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]

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]

And it's not a neutral conductor.

 

[ipf]

And it's not a neutral conductor.

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

 

[Soi disant]

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]

@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]

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]

@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]

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]

@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]

@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]

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.

 

[Rockingit]

I think I walked into a neutral bar in Singapore once, didn't stay long.

 

[telectrix]

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.

that's what i said.it's no longer a neutral as it's not referenced to 0v any more. you seem to have a penchant for twisting posts to suit your own ideas.

 

[timhoward]

Another thing which is not going to help anyone is loose, sloppy, terminology.

I think you are taking this a tad far!
It would appear from your logic that you'd like me to write "Broken line conductor which used to be a neutral conductor before it was broken and is insulated using black pvc according to pre-harmonised standards" on reports. I think I'd prefer to be loose and sloppy. You should try it too. The liberation feels amazing!
In fact I've just said "Neutral" to another sparky even though it isn't connected yet. Astoundingly they understood me. It felt great!

 

[Soi disant]

that's what i said.it's no longer a neutral as it's not referenced to 0v any more.

Well, actually no, you didn't, you said this (with my emphasis):

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.

And that's not me twisting things, and again, it's not me trying to start a fight. It's me trying, and failing, to get across what I think is a very important fundamental point.

If you had a 9V battery, with a bulb connected across it, and you disconnected, at the battery, the wire attached to the -ve terminal, it would no longer be a -ve wire. Were you to connect a voltmeter to it to measure what voltage it was at wrt battery - you would find that it was at +9V, and you would not be able to measure -9V between it and the battery +. It wouldn't be a -ve wire.

Of course this distinction doesn't matter most of the time when you're talking about the wires from the bulb holder, ditto the N conductor as per above, which is what I'd already said in #15, so in no way am I arguing with

In fact I've just said "Neutral" to another sparky even though it isn't connected yet. Astoundingly they understood me. It felt great!

It's just that when someone is trying to get to grips with what is meant by "+9V", or "230V AC", about what potential differences exist between what points in a circuit, and when, and why, and why current flows, or does not flow, I think it is important to focus very precisely on what something actually is.

I'm sorry that I'm failing so badly to explain that people think I'm really trying to make trouble.

 

[timhoward]

I'm sorry that I'm failing so badly to explain that people think I'm really trying to make trouble.

I do think there has been some misunderstanding of intent. Trust me you have explained your point!
Sorry I was flippant. I just didn't want the poor chap to go off and become a plumber while we were arguing how best to describe a disconnected line conductor (and in fact his original post suggests he already understood this as a line conductor!)

(I also meant to say thank you for reminding me of the 325v peak waveform - it's been a long while since I did the x 1.414 maths for a WYE configuration)