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Neutral in electrics?

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Family
529920.  Mon Mar 30, 2009 11:34 am Reply with quote

Having just watched the repeat of 'Electricity' last night on Dave ja vu, it has reminded me of something that I have never understood, and have never succesfully found any information about.

What purpose does the neutral serve in an AC electric circuit?

Thanks for any light you may shine on this.

Regards,

Julian

 
Ion Zone
529963.  Mon Mar 30, 2009 3:17 pm Reply with quote

Do you mean the earth wire?

 
Sadurian Mike
529994.  Mon Mar 30, 2009 4:32 pm Reply with quote

Live - Neutral - Earth.

(Remind me not to ask Ion Zone to rewire my plugs).

As I understand it (and I am certainly no expert), the Live carries the current from the generating source (battery or mains input) to the device, and the Neutral carries it away from the device being wired in.

The Earth is there to carry away any electricity that somehow escapes the confines of the wires and gets into the body of the device (electricity preferring to go down the Earth wire than through the relatively non-conducting material surrounding it).

 
bobwilson
529995.  Mon Mar 30, 2009 4:34 pm Reply with quote

Quote:
As I understand it (and I am certainly no expert), the Live carries the current from the generating source (battery or mains input), and the Neutral carries it away from the device being wired in.


I was about to say that but then realised it doesn't make sense. In an AC circuit, the current switches direction x times a second - that's why it's AC not DC.

 
Posital
529997.  Mon Mar 30, 2009 4:35 pm Reply with quote

The cover of Hawkwind's album PXR5 was banned because it showed a plug wired to kill on the back... can't find a pic on the net... :-(

They put nasty big red stickers all over it after a while...

 
Posital
530000.  Mon Mar 30, 2009 4:37 pm Reply with quote

Live - it's a complex thing as you need to understand how mains electricity gets to us... three phases and all that...

back in a mo...

 
Sadurian Mike
530006.  Mon Mar 30, 2009 4:56 pm Reply with quote

Yipes. I just read the Google page and came out none the wiser apart from to offer a small apology to Ion Zone.

Apparently, in trade two-wire circuits the Neutral can be connected to the Earth.

 
mckeonj
530010.  Mon Mar 30, 2009 5:02 pm Reply with quote

In the UK and Ireland, when wiring plugs, all you need to know is:
Brown is Live at 240 volts and it can kill you
Blue is Neutral, usually zero volts, but may go higher, don't trust it
Yellow/green is Earth; should be totally safe under normal conditions.
Don't worry about 'three-phase' supply, leave that to the professionals.
In foreign countries, don't mess with their wires and plugs, they are all mad, bad, and dangerous to know; especially in North America.
I am referring to the electrical systems, not the people.

 
Ion Zone
530017.  Mon Mar 30, 2009 5:09 pm Reply with quote

Quote:
Live - Neutral - Earth.

(Remind me not to ask Ion Zone to rewire my plugs).


Oh yeah, sorry, it is confusingly named.

 
mckeonj
530022.  Mon Mar 30, 2009 5:13 pm Reply with quote

To answer the original question; the purpose of the neutral is as a reference against which the live voltage varies with time.
The neutral reference is normally zero volts with respect to ground, but may vary under certain conditions.
To explore this further requires mathematics with which most of us are not comfortable.

 
bobwilson
530035.  Mon Mar 30, 2009 5:31 pm Reply with quote

so is it that the neutral wire stays at zero volts with respect to ground, and the live wire varies between +240v and -240v? Is that how it works?

 
bobwilson
530036.  Mon Mar 30, 2009 5:34 pm Reply with quote

Quote:
In foreign countries, don't mess with their wires and plugs, they are all mad, bad, and dangerous to know; especially in North America.


I totally agree - one of the areas of excellence in the UK is the domestic wiring - why no other countries have followed the three wire / safe wire system I have never understood.

 
Posital
530049.  Mon Mar 30, 2009 5:58 pm Reply with quote

Electricity arrives across three wires that are 120 degrees out of phase...

Each of these will supply a different area or estate... the neutral is basically the sum of all three phases and is generated from the centre of a Y (wye) transformer:



From memory, neutral tends to hover around 5-10V relative to earth.

 
bobwilson
530051.  Mon Mar 30, 2009 6:00 pm Reply with quote

thanks Posital - that really clarifies it (not!).

 
bobwilson
530052.  Mon Mar 30, 2009 6:00 pm Reply with quote

thanks Posital - that really clarifies it (not!).

 

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