Date   : Fri, 04 Sep 2009 08:25:46 +0100
From   : info@... (Sprow)
Subject: Leccy @ Acorn World '09

In article <090903235504@...>,
   Jonathan Graham Harston <jgh@...> wrote:
> > because each socket  has two cables feeding it from either side of the
> > ring effectively doubling up the rating. (Say 38 amps to be on the safe
>  
> Nooooo. times SQR(2), not times 2. Check your parallel resistance
> calculations.

Say one cable is 1 ohm, then the resistance of such 2 cables is

 [ (1/1) + (1/1) ] ^-1

which is 0.5 ohms. That's a straight factor of 2.

Maybe you're thinking I^2 R for the power lost due to heating the cables?
If each cable is rated individually (due to the plastic it's sheathed with
and the trunking it's installed in) to, say, 100W then Imax = 10A.
To keep the total power dissipated in the trunking constant at 100W the new
Imax is 14.14A,
Sprow.