[Gllug] OT: Mains electricity colour coding.

[Christopher Hunter]

On Sun, 2010-10-24 at 18:58 +0100, general_email at technicalbloke.com
wrote:
> Hi All,
> 
> For time immemorial I have been told brown is live, blue is neutral and 
> yellow/green is earth. Mains electricity is AC so it oscillates between 
> the positive and negative 50 times a second right? In that case why does 
> it matter which way you wire the blue and brown cables to the nominally 
> blue and brown terminals in a plug? I always assumed you could 
> electrocute yourself equally well by touching the blue terminal, maybe 
> even better as the brown's got a fuse that might protect you!
> 
> I'm slowly working my way through W.P.Jolly's seemingly excellent "Teach 
> Yourself Electronics" so maybe it'll all become clear soon, having said 
> that - I'm also impatient!
> 
> I'm wondering now if and how the notion of "live" and "neutral" is 
> different to that of "positive and negative". If so can anyone breifly 
> explain or point me to a website that explains? Haven't had much joy 
> with google so far :/
> 
> Yours ignorantly,
> 
> Roger.

Mind your fingers, Roger!  

The Neutral is actually the current return, and is connected to a
"star-point" earth at the nearest substation.  In an ideal situation,
the Neutral would be at 0 Volts, with the Live varying around it.  In
reality, there's finite resistance in the way of the neutral to earth
path, so the neutral will float a few volts above Earth (actually
varying, like the Live).  You shouldn't get more than (roughly) 8 - 10
Volts on the Neutral in a reasonably good domestic installation.

So - the supply comes to you down the Live conductor, and goes back down
the Neutral.  The Earth is just there for protection.  

If you want further details, pictures, and some references to good basic
electrical theory books, drop me an email.

Chris



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