Wrong Polarity??????

[jujubean]

Guys...a daft question I know
Why is the neutral terminal 0 volts when Alternating voltage changes polarity 25 times a second ?
In theory surely the N terminal should become live as the supply voltage alternates
Told you this was a daft question and is probably painfully obvious to those with brains
Cheers

 

[Spark123]

The polarity changes 100 times per second
It appears as 0v(*) with respect to earth as it is bonded to earth at the supply transformer. There will be a slight rise in potential above 0v caused by the impedance of the cable and current flowing down it.

 

[Steve]

Depending on the earthing system in use in your area, the neutral may also be bonded to earth at several points on the way back to the substation / transformer.

 

[bernardgreen]

There is no such thing as " a voltage ". There are voltage differences and all voltages should be declared as Xvolts relative (or referenced to ) something else. That is why volt meters have two leads.

So Neutral is ( tends to ) 0 volts referenced to earth

Live wire is 230 volts AC referenced to the Neutral wire.

 

[Dippy]

Actually there IS such thing as a "voltage", but indeed it is inherently a potential difference. Consider the SI definition: A volt is the potential difference across a conductor when a current of one ampere dissipates one watt of power.

 

[jujubean]

The polarity changes 100 times per second
It appears as 0v(*) with respect to earth as it is bonded to earth at the supply transformer. There will be a slight rise in potential above 0v caused by the impedance of the cable and current flowing down it.

Of course you are right my friend ...What was I thinking of ?
Okok how bout this...50 times a second the meter on the live terminal should display +230 volts and 50 times a second it should display _230 volts but I know our meters will treat both negative and positve waves as positive
My way of thinking (for whats its worth) is that in conventional current the electrons will travel from the higher potential to the lower ..ie..(+230 to 0volts (neutral)...and from the negtive half of the sine wave the current will run fro 0 volts (neutral ) to the -230 volts..Which of course is the opposite direction
Tell me if this makes sense
Cheers [/list]

 

[baz1968]

Dippy is right, all voltages are a potential differance, therefore 230 volts is a potential differance with reference to 0 volts Neutral/Earth. What a lot of people fail to realise is the current carrying capacity of a neutral conductor. When it is continuos throughout a circuit this current is assumed to be zero and is for reference only, but break a neutral and take hold of both ends and the full load current for that circuit will be passed through your body, as some people have discovered the hard way. Bet they did'nt do that again.

 

[2891]

Where do you get 100 from?

Frequency as we know is based on cycles per second. so one cycle will mean (lets start at 0) rises on the positive to 230VAC rms, falls to 0 and goes to -230VAC rms. this is one complete cycle. so one second divided by 50Hz = 0.02 So you only get 25 "positive" cycles and 25 "negative" Cycles per second.

 

[electronicsuk]

Where do you get 100 from?

Frequency as we know is based on cycles per second. so one cycle will mean (lets start at 0) rises on the positive to 230VAC rms, falls to 0 and goes to -230VAC rms. this is one complete cycle. so one second divided by 50Hz = 0.02 So you only get 25 "positive" cycles and 25 "negative" Cycles per second.

The 100 figure comes from the question posed by the OP:

Guys...a daft question I know
Why is the neutral terminal 0 volts when Alternating voltage changes polarity 25 times a second ?

Now, I'm not sure how you figured that at 50Hz there are 25 positive and 25 negative peaks/second. You (2891) quite rightly say that in one complete cycle voltage goes to +230VRMS, to 0, to -230VRMS, and then back to 0. Times this by 50 and you'll find there are 50 positive and 50 negative peaks in a period of 1 second, not 25. This amounts to a change in polarity 100 times every second.