As a note: As an
Electrician I have connected one of these 24O volt US clothes driers for some
US citizens that migrated here. I still required a 240/120 volt step
down transformer to control aspects of the drier, such as the light inside the
drum and the motor that rotated it. (Australians in dry
climates typically use clothes lines located outside in the Sun rather
than a clothes drier.)
I don't
understand why Americans who migrated to Australia can't buy an Australian
clothes dryer. I'm sure they must exist. To import a clothes dryer from
the states, modify it so it will work in Australia has to be expensive.
In addition what happens when it breaks and parts are not available?
What about replacement 120 V bulbs? Or other such
parts?
What
about the cycle timer that runs at 120 V, but designed for 60 Hz? If it
is run at 50 Hz, it will run slower, and hotter if run at 120 V. Most
cheap 50/60 Hz motors are designed for 220 V @ 50 Hz and 240 V @ 60 Hz.
Or 110/120 @ 50/60 Hz.
I have
a fully electric dryer that runs at 240 V. The circuit feeding it is
rated for 30 A. It connects with a 3 wire plug. The third plug is
the safety ground (earth). If there is any component inside that needs
120 v, maybe even 24 V, it is derived internally from the supplied 240
V. There is no need for an external or additional transformer to supply
the 120 V transformer that you mentioned above.
Australian and
European systems
use 220 - 240 volts at 50
hertz, and as such we can use half the size of the
conductors the USA requires to supply the same load at 120
volts.
The USA uses 120
volts nominal at 60 hertz for general fixtures (eg washing machines, TVs. etc.), and uses
240 volts nominal at 60 hertz
for higher loaded appliances (eg clothes
driers and large air-conditioners). I have been
informed that while 120 volts is safer than 240 volts in the event of an electrocution, it can be the cause of more electrical fires that
begin due to the higher current
being drawn on faulty conductors or
joints.
Electric
stoves also run on 240 V. Some heavy duty tools, such as some air
compressors may require 240 V to operate.
The air-conditioner in my home is rated at 240 volts and 15 amps at a power factor of
0.7. This is the maximum sized unit allowed in Australia on a single
phase. Larger units must
be connected to a three phase
supply, which is due to starting
currents that can be several times higher
than the running current. Each of the phases to neutral is 240 volts at 50 Hertz. Between any two phases is
415 volts at 50 Hertz.
A single phase unit in the United States
is permitted to draw up to
40 running amps. I
presume this is most likely due to the complexity
involved in the supply
of three phases to the suburban home.
The American
system of using a centre tapped transformer, and grounding the centre tap is
known as the Edison system. I guess Thomas Edison must have devised
it. It was devised in a time when copper was abundant and cheap
and people thought the extra cost of the of having larger conductors was
better than the chance of being electrocuted with higher
voltages.
The European
standard was chosen because cost was considered more important. The
Europeans put a greater effort in designing plugs and sockets that were shock
resistant. That is by the time the contacts of the plug are exposed to
possible contact with fingers, the pins are no longer touching anything
live. Even light sockets are designed so that by the time the bulb
thread is exposed it is no longer in contact with the socket contacts.
Thus if someone came in contact with the contact while changing a bulb, the
person would not be shocked.
The European
system was designed to also save money by not employing a transformer to
derive single phase from 3 phase. This way 3 phase can economically be
brought into the home. Motor and heating devices that run more
efficiently at 380 - 415 V can be connected across the line in delta if no
neutral is needed, and in Wye, if the neutral is needed. Single phase
220 - 240 V can be derived from a line to centre tap (neutral)
connection. Similar to a Wye.
In the US
industrial voltage (3 phase) is almost always 480 V. 240 and 208 V are
used seldom. 208 V, mostly for lighting. 480 V line to neutral
voltage is 277 V (480/3^-2, which there is nothing made to run at this
voltage. We don't use 415 V for anything, so we can not use the European
system to get 240 V line to Neutral. If we want 240 V, we have to
transformer it from 480 V. A cost item.
In some plants, lighting is balanced around a
3 phase 208 V system. The lights are all 120 V and are connected line to
neutral. Doing it this way, you can connect more lights economically
then on a two wire or even a three wire system.
Because of the Edison system in use, it is
not economical to bring 3 phase into the home. In order for each home to
have both a 3 phase and single phase system using 480 V (or even 240 V) and
120 V a costly transformer(s) would be needed in each home to provide both
forms of power. so, we are stuck with what we got.
I remember when I was in Korea in the early
90s. They were switching everything from the 3 wire American inspired
Edison system to the European system. All the plugs were changed from
the two flat pin type to the Schucko type used in Europe. There reason
was better economy at 240 V. They did however keep the 60 Hz
frequency.
John
