Date   : Mon, 07 Sep 2009 15:43:56 +0200
From   : rick@... (Rick Murray)
Subject: Leccy @ Acorn World '09

Rick Murray wrote:

> The concept of a "ring main" causes great distress to the French.

It may be, all claims of supposed benefits aside, that I may have 
uncovered the origin of the British peculiarity - the ring main.

--8<--------
The ring circuit was devised during a time of copper shortage to allow 
two 3 kW heaters to be used in any two locations and to allow some power 
to small appliances, and to keep total copper use low.
--8<--------

[source: http://www.statemaster.com/encyclopedia/Ring-circuit ]


Mick Champion wrote:
 >> I agree and think radials make safer circuits. With a ring, we rely
 >> on the two ends to be continuous. How would you know if they are not?

And JGH replied:
 > Competant installation and testing. I can do you a whole-house
 > installation test and certification for 50 quid [plus travel! ;)]

This leads to a very obvious problem that there is no accounting for 
entropy. You are making a circular circuit and burying it behind 
plaster. In 99.9% of cases it will function as expected. But dampness, 
corrosion, rust, insects, animals, sub-par workmanship or materials, 
earth tremors (whether seismic or man made (i.e. nearby heavy traffic 
etc))... all can contribute to the situation where your ring is actually 
a radial. No little '!' will flash. No warning light will come on, and 
you will now be using a cable that may be underspecified for the load it 
is now carrying.


Best wishes,

Rick.

-- 
Rick Murray, eeePC901 & ADSL WiFI'd into it, all ETLAs!
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