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More info?)
In comp.sys.ibm.pc.hardware.storage Tomi Holger Engdahl <then@solarflare.cs.hut.fi> wrote:
> nagesh_pandher@hotmail.com writes:
>> Can you please explain "ring main GPO ccts"?
>> I am totally nontechnical.
> Here is some explanation of UK wiring (from www.epanorama.net):
> UK wiring is somewhat special case. The UK is unusual in having fused
> plugs as standard (according BS1363 parts 2 and 4). 13A max in
> eachplug, and 30A at the panel for each ring. Maximum current at wall
> outlet in the UK is for 13A. The plugs carry a fuse holder and the
> fuse should be rated to suit the appliance used (fuse rating from 1A
> up to 13A exist). The fuse in the plug is for protecting the cable to
> the appliance, not the appliance itself. For the latter, the appliance
> would have its own fuse (or other suitable protection means). Neutral
> is neither switched nor "protected". UK mains plugs are polarized. In
> the UK, a wiring system known as a ring mains is used. UK standard
> (for the last 30 years or so) has been the ring -main (domestic and
> commercial) rated at 30/32A @230V. A single cable runs all the way
> round part of a house interconnecting all of the wall outlets. This
> will be protected by one large fuse in the fuse box. A typical house
> will have three or four such rings. The power rings are normally
> protected by a 30 amp fuse and the lighting rings by 5 or 10 amp
> fuses. Those fuses protect the wiring, not the appliances so, every
> appliance carries its own fuse in the plug.
> The design philosophy of e.g. the German system (Schuko) is that a room
> (or a small number of rooms) has a 10 A or 16A fuse in the consumer
> unit,
That fuse would be in the fuse box on tha wall. 10A for light, 16A
for power outlets and e.g. 3*25A for an electric stove.
> and all leads and plugs are designed to withstand any
> short-circuit current that will not yet blow the fuse (today usually
> circuit breakers are used, not fuses). If a fault occurs, a circuit
> breaker is trivial to reset, The fuses are generally in the main
> distribution panel. The fuse inside equipment will provide the
> protection agains constant overload. This equipment fuse is rated
> based on the power the equipment might take, and the wire
> going to equipment must be thick enough to handle that load current
> that this fuse can pass before breaking.
Actually there is no requirement for a fuse in the equipment itself,
depending on what type of equipment it is and what kind of cable it
has. If it has 1.5mm^2 cabeling, then the main fuse is enough, since
the wires in the wall are also 1.5mm^2 and these are rated for 16A
continous current and several thousands for a short duration
short-circuit. It is also permissible to use lighter cables
(0.75mm^2) for lighter equipment. This type of cable should
still be able to stand 16A for some time.
For the british system in equipment without a fuse in the plug
you would need something like 1.5mm^2 cables to all types of
equipment. A 0.75mm^2 cable would likely have problems at 32A.
Remember that power goes with the square of the current in
cables, so the 0.75mm^2 cable would actually get heated up
four times as trong as it would in germany with current that
just about does not blow the fuse.
As a result the british need additional fuses in thinner cables.
I would guess that for 2.5mm^2 cables the british can do without
the fuse in the plug.
Arno
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