On 4/3/2011 7:57 AM, Charles Harpole wrote:
> Maybe being in Thailand, where 230vac is supplied with TWO wires, makes me
> ask.... what is 4-wire 240vac service?
Charles,
There's a tutorial on Power and Grounding for Audio and Video Systems on
my website that explains most of what you want to know, and it covers
variations in practice over most of the world.
http://audiosystemsgroup.com/publish.htm
In general, the "Service" is the wiring between the power company and
you. In most of North America, homes get three wires -- both ends of a
240V center tapped transformer plus the center tap. The center tap is
the neutral, usually grounded at the power company's transformer and
which must be grounded where it enters the home.
Larger buildings are wired with 3-phase power, usually in a Wye
configuration, with three 240V hots plus a neutral. See the tutorial
for more detail.
Inside buildings, an appliance like a clothes dryer that needs 240V
power, would get both sides of 240V plus the ground. IF that appliance
also needed 120V power, the neutral wire must also be connected, and the
120V load must be connected between one side of 120V and neutral.
The same standards (and laws of physics) apply in your part of the
world, except that voltages are multiplied by two and currents are
divided by two for the same load.
73, Jim Brown K9YC
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