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[OM] Re: OT Rant: No more $$ to Europe! - Mains wiring

Subject: [OM] Re: OT Rant: No more $$ to Europe! - Mains wiring
From: Brian Gray <bandvg@xxxxxxxxxxxxxxxxx>
Date: Thu, 15 Apr 2004 22:00:24 +0100
Chris wrote

 >It's a bit strange then that only one wire shows a current when tested
 >with an 'electrical' screwdriver - and it's always the same wire.

 >On 14 Apr 2004, at 05:46, Daniel Tan wrote:

 >
 > There actually isn't any difference - it's labelled like that to
 > conform
 > to a convention or standard. The AC wave can start on either...

In UK homes, the neutral wire is at approximately the same voltage as earth 
(ie 0 Volts) if everything is working properly.  The voltage on the live 
wire varies on either side of this (plus or minus about 240V).  Hence only 
the live wire should light a neon in a test probe.   (A pseudo electrician 
trying to fit a wall light for me recently was baffled when he connected it 
up in such a way that both pins in the socket lit the neon in his probe BUT 
a light bulb did not illuminate.)

        Nowadays most (all?) electrical equipment using the mains that is sold 
in 
the UK is fed through an isolating transformer . but in days gone by it was 
not uncommon for the hidden chassis of radio/TV equipment to be wired up so 
that it could be at 240V .
        Incidentally, our Hifi buffs might be interested that when using 
sensitive 
pre-amplifiers for acoustic measurements on to Ampex tape recorders in an 
industrial situation I once discovered that using centre tapped 240 volts 
(ie +120 to -120V) for the supply  instead of  0 to 240 volts between live 
and neutral caused a drastic increase in the noise levels of the signal 
when the equipment was used with all the normal earthing arrangements for 
wiring etc.  It was only when looking for the cause of the poor S/N that we 
discovered what was coming out of the special socket installed for us in an 
area which was not normally served by 240 Volt supplies.

Brian 


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