On Wed, 22 Aug 2007 16:02:42 -0700, Pete C
wrote:

AIUI in Holland proportionately to population, the number of people
killed by electrical accidents is /half/ that of the UK, and I don't
think they have ring mains... do they?

The numbers killed in electrical accidents isn't recorded very
consistently between countries. For example some record only
electrocution deaths, some would record deaths in a fire caused by
electrical faults as "caused by electricity" others as a fire death.
There are certain countries in the EU with dire standards - France,
Spain, Portugal, Italy, Greece and most of the old East Europeans
states amongst them. In these countries deaths primarily caused by
electrocution are fairly common.

From a hazard point of view fixed wiring (even French) doesn't cause
many accidents directly. The direct difference between ring and
radial is also minimal. However, the consequential hazards are not.
A characteristic of many continental installations is that there are
a smaller number of sockets in a house than for a house of similar
age in the UK and consequently much more use of trailing extensions.
These are inherently more hazardous than wall sockets and contribute
to far more fires of electric origin than does fixed wiring. The
lack of any form of appliance lead protection coupled with high trip
currents also makes fires caused by equipment failure more common on
the continent than in the UK.

All countries using the CEE 7/4 (Shuko) plugs tend to have a number
of child fatalities each year caused by objects being poked into the
unprotected openings. The UK has virtually no such accidents with
the shielded 13A socket.

The Schutzkontakt (Shuko) plug socket pair is designed to be safe in
that the side earth contact must mate before the pins and the
recessed socket prevents fingers touching the pins as they are being
inserted. Unfortunately there are a number of other systems using the
same or similar pin sizing and spacing as Shuko but without the earth
connection or recessed socket. As a result there are accidents
caused by plugging Shuko plugs into sockets where the earth is either
absent or ineffective as it doesn't touch the side contacts. A
further catch is that in such situations the side contacts on the
plug become live so giving a shock to anyone who tries to remove it
in such fault conditions. This commonly occurs with the two pin CEE
7/16 (Europlug 2.5 A/250 V) unearthed socket which isn't supposed to
fit a Shuko plug but many will. The French 2 pin plug with female
earth will also usually fit a Shuko socket - but without the earth
making. The CEE 7/7 is a cross between the Shuko and French systems
with side contacts and a female earth receptacle and usually supplied
with new equipment.

Although rated at 16A it is also possible to buy Shuko plugs with
considerably lower current carrying capacity and many "Shuko" plugs
are of poor quality and prone to overheating when running at high
loads. I have seen some dire examples around of very poorly made
Shuko plugs and nothing like the same poor quality in even the
cheapest BS 1363 plugs (probably because BS1363 plugs require third
party certification whilst manufacturers can self certify Shuko).

Another issue with the continental two pin plugs is that the wiring
of the live and neutral is random (and even if it were not the plugs
can be inserted any way around). Usually this isn't an issue but it
becomes one when freestanding lamps using Edison Screw (the
continental standard) fittings. The threaded part of the shell can
be left live and shocks while changing bulbs and accidentally
touching the bulb thread are common. The shock isn't usually fatal,
the fall off the ladder more often is!

There is no question that BS 1363 is a fundamentally much safer
system than the Shuko and its variants. This is hardly unexpected as
the Shuko design dates from the 1920's.

The improved safety of the ring over the radial stems largely from
secondary effects of the greater number of fixed sockets and fuse
protection of the appliance lead. Together these reduce the number
of fires caused by overloaded and damaged extensions. There is of
course nothing to stop you wiring a BS1363 layout in radial form -
but there would be no advantage in doing so.
--
Peter Parry.
http://www.wpp.ltd.uk/