Hi Nick,
Many thanks for your time and explaination that gives me a new view of UK
fused plug.
Best regards,
Raymond Li
=========================================================
"Nick Rouse" <[email protected]> on 18/11/99 06:13:48 a
To: Raymond Li/DixonsNotes
cc:
Subject: Re: internet information
----- Original Message -----
From: <[email protected]>
To: John Allen <[email protected]>
Cc: <[email protected]>
Sent: Wednesday, November 17, 1999 3:20 PM
Subject: RE: internet information
>
>
>
>
> John,
>
> I am very insterested in your explaination on fused plug requirement
> between the ring main supply system and branch or spur systems. Could
you
> please shed more light on to me about the fused plug requirement on the
> ring main supply and a simply way to identify the said main supplies.
>
Raymond
Practically all UK domestic premises and the vast bulk of UK low power
single
phase outlets in commercial and light industrial premises use plugs and
sockets to
BS1363. They is a legal requirement for all new installations in domestic
premises.
If you have not come across them, they are jumbo sized square 3 pin plugs
rated at a
modest 13A. An essential part of the specification and design of this plug
is that
it contains a fuse to BS1362. As far as I am aware this design of fuse is
not used
anywhere else.
The normal way to wire up domestic premises in the UK is to use a ring main
system.
Typically all the socket outlets on each floor are connected to a ring of
two
conductor plus earth cable that runs from the fuse box around the rooms on
that floor
and back to the fuse box.
Heavy current devices such as cookers and water heaters are wired
separately
as is fixed lighting.
Each ring main is protected at the fuse box by a fuse or circuit breaker
that is rated
for the wiring of the ring main, typically 30A or 50A.
A large proportion of electrical fires in domestic premises are caused by
damage
to the power cord between the wall socket and the appliance. If the
insulation
of low current rated power cords is damaged it is quite possible to have a
partial
short circuit in the cable that allows sufficient current to flow through
the cable
to cause serious overheating without taking out the high rated fuse
protecting the
ring main. Since this current is not flowing in the appliance, the fuses
there are of
no help.
In industrial wiring practice it is normal to insert a fuse or breaker
every
time a
low current rated spur is taken off a higher rated feed at the point it is
spurred off.
In this way all cable is protected by a fuse appropriate to the rating of
the cable.
This principal is extended to domestic wiring in the UK.
Because it is not known in advance what the rating of the power cord
plugged
into any wall socket will be, the fuse cannot be fitted in the socket. It
is
therefore
fitted in the plug. This system has the advantage that low rated cords can
be used
safely for low rated appliances.
You ask how to distinguish between ring and spur circuits. This question
does not
normally arise for suppliers of equipment to the UK market. UK law requires
that
all electrical appliances sold for domestic use are sold with a power cord
fitted
with a BS1362 plug containing a fuse appropriate to the rating of that
power
cord.
These regulation also cover thing such as office equipment and personal
computers
that might reasonably be bought for domestic use.
I hope this helps clear things up a bit for you
Regards
Nick Rouse
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