http://www.sea.siemens.com/step/templates/lesson.mason?electricity:1:1:1
----- Original Message -----
From: <julian_davies@xxxxxxxxxxxxxx>
To: <olympus@xxxxxxxxxx>
Sent: Friday, April 16, 2004 6:37 PM
Subject: [OM] Re: OT Three - phase mains (was OT Rant: No more $$ to
Europe!)
> Close....
>
> In the distribution system, the neutral wire is indeed
> neutral, and is normally earthed at the sub station
> transformer (note, not the same as your local earthing
> wire!!!). Because the three phases are divided to have
> approximately equal use, there is no significant net
> current flow in the wire.
> Within your single - phase home, however, it has only
> one phase of return current flowing in it, which means
> that there IS a net current flow, and due to the
> resistance of the wire, a potential, whose size
> depends on the current flowing and how far it is to
> the substation. So don't treat it as naturally safe -
> that's what the local earth wire is!
>
> Julian
>
> PS this is a neat way to save copper, since for a
> three - phase mains distribution system, you only need
> wires for the three lives. The common neutral (which
> should be wire 4) is formed by the earthing at the
> substation and at the generating plant.
>
> PPS you really don't want to get one of those 415V
> cross - phase shocks.
>
> --- Chris Barker <ftog@xxxxxxxxxxxxxxxx> wrote: >
> > Thanks Piers. I must admit that AC electricity has
> > always had me
> > somewhat puzzled; I tamper with ring main wiring
> > with great caution!
> >
> > Chris
> >
> > On 15 Apr 2004, at 11:46, Piers Hemy wrote:
> >
> > >
> > > Quite right, Chris, and (as far as UK supply is
> > concerned) quite wrong
> > > Daniel, in the sense that you would be ill-advised
> > to mix them up!
> > > But I
> > > will be happy for Tim Hughes to tell me otherwise
> > (again!).
> > >
> > > Thw neutral wire *is* neutral, with zero current
> > flowing, when the
> > > entire
> > > system is running properly - the entire system is
> > a three-phase AC
> > > system,
> > > able to provide 415V three-phase, and 24v from any
> > one phase. For
> > > domestic
> > > supply, single pahse is the norm, and assuming all
> > three phases are
> > > balanced, there will be no current flowing on the
> > neutral (which is
> > > common
> > > to all three pahses).
> > >
> > > It was a question that bugged me at school too
> > (thinking of James
> > > Royall's
> > > original question) but I got the answer in
> > Chemistry rather than
> > > Physics
> > > class. Put that down to the approachability of
> > the teacher.
> > >
> > > Piers
> > >
> > >
> > <|_:-)_|>
> >
> > C M I Barker
> > Cambridgeshire, Great Britain.
> >
> > +44 (0)7092 251126
> > ftog at threeshoes.co.uk
> > http://www.threeshoes.co.uk
> > http://homepage.mac.com/zuiko
> > ... a nascent photo library.
> >
> >
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