| email@example.com wrote in message
|> Radial circuits are the norm in the USA. I've never seen a loop circuit.
|> I understand the UK has these wire with a higher amperage and fuses in
|> each socket for the lower amperage to be supplied.
| Almost, the ring main circuit is fused at 30A, the fuses for each
| appliance are in the plug, not the socket. 3A and 13A are the most
| common fuses in plugs, but other ratings are available up to a maximum
| of 13A. If the fuse was in the socket, then you would have to change
| in when, for example, you unplugged a kettle, and plugged in a table
| lamp to the same socket. Anything plugged into a standard uk 13A
| socket, e.g. a shaver adapter, has to contain a fuse, as if it did not
| the only protection would be the 30A fuse or breaker in the consumer
| unit, which is far above the capacity of the appliance flex. These 13A
| BS 1363 rectangular pin plugs are the only ones normally used now in
| domestic and office type environments, and are normally wired in a
| ring main. They always have three pins. There was an older standard,
| BS 546, which specified round pin plugs, rated at 2, 5, 15 and 30A.
| These were not internally fused, are seldom seen now, except for the
| 15A, and less often the 5A ones, which are still used for stage
| lighting purposes. I don't know why we wire our 13Asockets in ring
| mains; somebody once told me that it was to reduce the use of copper
| after the second world war, when it was in short supply, but I don't
| know if this is true.
I guess my USA thinking influenced by understanding of some previous
info. In the USA, our receptacles are 15 or 20 amp, and appliances
are supposed to insure they are protected internally of lower levels
of overloads, if applicable. The wire itself can be rated for what
the applicance will use. If an appliance would overuse current then
it is the appliance that should blow its own fuse. The difference
between having the fuse in the plug and in the appliance would relate
to any overload on the wire itself. But the wire doesn't overload,
though it could short out, which would trip the breaker for the circuit.
What I assumed was that the socket was protected by a fuse at the level
suitable for cord short circuits since the loop circuit in the wall was
rated rather high. But with a fuse in the plug, the cord wire is well
In your case, a short or overload should blow the plug fuse well before
the house fuse/breaker. Do plugs come with circuit breakers instead of
Now the question is, does the circuit in the wall run back to the same
breaker at the end, or does it just come to and end and stop? One would
be a loop and one would be radial.
What current levels are used for electric stoves, ovens, hobs, etc?
We have them here up to 60 amps and they run on 240 volts (120 amps
on 120 volts would be rather undesireable).
| For industrial use at higher current ratings, the most common are the
| connectors which were known as BS 4343, but which are now BS EN 60309.
| These are the colour coded plugs which have 3,4 or 5 pins recessed
| within a circular plastic surround. Versions here are rated at 16,
| 32, 63 and 125A, in the USA, they are rated at 20, 30, 60 and 100 or
| 120A, I can't remember which, and I don't know the standard number for
| them. They don't seem to be as widely used over there as they are
You might be referring to the IEC pin-and-sleeve connectors. Those
go all the way up to 690 amp versions (yes, six hundred and ninety).
| British electrical distribution is very different to that in the USA.
| Over here the most common voltage is 11kV, but other Voltages, 6k6V,
| 22kV and 33kV for example are also used. We use relatively large
| three phase transformers in substations, not the small things stuck up
| poles that you have over there. The output from the substation is a
| three phase four wire star connected system. The neutral is connected
| to the star point, which is earthed (grounded).
How many homes would be on a single substation?
What would be the total current rating for that substation secondary?
What would be the fault current if there was a solid short circuit?
I prefer the small transformers for fewer homes, as it keeps the fault
current levels low. But in dense urban areas, where transformer space
is at a premium, there is often what is called "network service" which
is a substation with a larger 3 phase transformer bank (sometimes more
than one in parallel). The voltage is 208/120 in the star configuration.
Customers are supplied with either three phase, or if they only need
single phase, they are supplied with 2 of the three phase lines.
| The nominal Voltage is 400 from phase to phase, and 230 from phase to
| neutral. Until recently it was 415/240, but nothing has really
| changed, it was a European harmonisation thing. All four wires are
| run along each street, in towns and cities normally underground, and
| all wires are taken into buildings requiring a three phase supply.
| Houses are normally supplied with only a single phase and neutral, the
| phases normally being used in rotation in each building along the
| street, so there is probably 400V between your mains sockets, and
| those of the house next door. A typical substation would typically
| feed several hundred houses, while large buildings such as factories
| would normally have their own.
Can you get just 2 phases if you have a need for 400 volt single phase
but not three phase? Is there equipment like circuit breakers and panels
designed for 2 poles like that, or would you just have to use 3 phase
stuff with one dead line?
| Several things to note; all three phases are symetrical about the
| earth point, we never have one with a higher Voltage on it. Our 230V
| is that Voltage from earth, it is not a centre tapped system with 115V
| on either side. We never have delta systems with one corner grounded.
| The Voltage is standardised throughout the country, you will not get
| anything other than 400/230V from the public supply, unless you are
| operating something *very*
large, like a railway, or a steelworks.
Standardizing the voltage like that is a big plus. In the USA it is a
mess. Much of that mess is because the use of Edison style split single
phase result in most appliances using 120 volts but some using 240 volts.
Commercial buildings have to use three phase because of the extra load,
but they get 208/120, which screws up 240 volt stuff. That's why some
240 volt delta, with Edison style split on one winding, is still used.
The extra B phase is then 208 volts to ground. And then these voltages
are too low for medium industrial use, so we have to have 480/277 as well
(Canada has 600/347). This resulted in lights designed for 277 (or 347)
volts. And all of this is really because Edison wouldn't accept AC (if he
had, then 3 phase would have made sense and the voltages would not have
the 2:1 ratio). Also, Edison was a bit paranoid about electrocution,
perhaps due to his mistaken belief that the neutral wire, when grounded,
would provide protection, and didn't realize its failure was because that
wasn't really a very good design.
I suspect 480 came about here due to the 60 Hz frequency. Crank up a
generator designed for 400 volt 50 Hz, so it runs at 60 Hz, and you get
480 volts. That, and transformers that can't go much above 400 volts
before starting to saturate at 50 Hz can do 480 with 60 Hz.
Personally, I think the ultimate solution would have been to never use the
neutral wire as a current carrying wire. Then you could simply have a
standardized line-to-line voltage that can be derived from either single
phase or three phased. For example, if 260 volts were chosen for that
standard, then 2 single phase windings at 130 volts, or 3 three phase
windings at 150 volts, would produce that voltage. Then heavy industrial
users can step to a higher (450/260 with my example voltage) level if they
need it. By making sure nothing was ever made to use the line-to-ground
voltage, it would keep things simple, while still having a voltage
suitable for heavy home usage without incurring too much current.
Plain 120 volts is inadequate. But we do have 240 volts here; it's just
that the ground tap is in the center instead of one end (which does reduce
the shock risk for humans standing in water). That in itself wasn't a
problem, but loads making use of it was where the voltage mess originated,
in my opinion.
Alternatively, I wouldn't be crying a single tear had the USA gone with
a system like the UK has, though with 480/277 at 60 Hz. But even 400/231
at 50 Hz would be fine (imagine if the entire world had gone with that).
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
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