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[aprssig] slightly OT:recessed male twist and lock

Dave Baxter dave at emv.co.uk
Tue Feb 7 11:34:47 UTC 2006


The UK does indeed have much the same system.

However, in domestic environments, there is always a 3 pole socket in
use. Line/Live/Phase (whatever you want to call it) a Neutral/Zero line,
and the safety Ground wire.  That last one makes first, and breaks last
when the plug is inserted/removed from the socket.  The plugs too, have
a fuse link in them in the Live side.  Switched sockets general only
switch the Live side.  (There are exceptions)

Many "Domestic" appliances are only 2 wire fed, being "Double Insulated"
so not needing a safety ground wire.  TV's, sterio's etc...  Even Power
Tools!

The "Neutral" is usually tied to Ground at the sub-station, and often
where the supply enters the premises.  The main circuit breakers (in the
consumer unit or distribution panel) interrupt both Live and Neutral,
the Ground is never switched.  Individual circuits are protected with
fuses or current sensitive circuit breakers.  There is often a RCD
(Residual Current Device, or as it used to be called "Earth Leakage
Circuit Breaker) feeding a group of circuits, before the individual
fuses/MCB's

3Phase, can be 380/400/440V (Root3 times the Phase-Neutral voltage) and
is usually supplied with the Neutral line, so you end up with up to 5
conductors in some industrial equipment power leads!..  Switching,
interrupts all 3 phases and the Neutral.  Equipment would usually be
designed to balance the load round all 3 phases, though it's not
strictly necessary...

Before the great EU, Europe had 220/380V, the UK had 240/440V.  Now it's
all be "Harmonised" to 230/400V or there abouts.  No actual change to
the supply voltages, just that the specifications and tolerances were
altered to cater for all the variations.

The other big difference of course is over hear in the EU/UK we use
50Hz, the USA/Canada use 60Hz.  Some parts of Japan have a right mix of
100V, to 220V, 50 and 60Hz, often all present in the same street (if not
the same building!)

AFIK the USA has 3 phase distribution, but each of the 3 phases is split
at the pole transformer to supply 110-0-110 to each house.  The "0"
should be at the ground potential also I think.  What used to amaze me
when I was there doing some non work (Hi Hi) was the pitiful reliability
of the so called "Safety Ground" continuity, as it often relied on the
metal trunking not a separate wire.

There has been mention of boats.  Take care!  Many boats have a double
diode device (anti-parallel) in the safety ground lead to shore, or a
full galvanicly isolated transformer (with no ground continuity boat to
shore) to prevent electrolytic corrosion of immersed metal parts.
(Different metals, salt water, etc...)

Take care All..

Dave G0WBX.

PS:	You do not know what pain is, until you step on an upturned 3
pin UK plug in the middle of the night with bare feet!  In that respect,
they are perhaps not so safe!.....





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