On Wed, 19 Nov 2003 20:03:39 GMT, Jane ) wrote:
snip
Confusion point:
The book states that a full load for a 120v 20amp circuit is:
120v x 20a = 2400 watts x 80% (safe capacity) = 1900 watts

Does that mean each one of those recepticles can have up to a 1900
watt load on them *simultaneously* without tripping the breaker, or
that *collectively* at any given time their load in summary shouldn't
exceed the safe capacity of 1900 watts total?

The reason I ask is this... the book also says that microwaves and
large appliances should have a "dedicated circuit." Do they simply
mean a dedicated wall outlet, or a dedicated circuit *breaker* --
meaning no other outlet is wired to that circuit breaker but the one
the appliance is plugged into...??

Because the way I read it, is I need a separate *circuit breaker* for
my washer/dryer outlet... one for my 1700watt treadmill (which can
also run a TV and lights in the garage, but then reaches the 1900watt
safe mark)... one for my garbage disposal and one for my microwave...

and the circuit breakers just keep adding up...!
snip

Yes, it's a bit confusing. It's the circuit breaker that limits the
maximum power that can be used by everything connected to it, whether
you have one outlet connected to a single breaker or 6 outlets, or 4
outlets and 2 ceiling lights, etc. Generally, a dedicated circuit
refers to a circuit breaker connected to a single load, whether it is
directly wired to it, as would be done for a dishwasher, or whether it
is wired to a single outlet, such as would be done for a microwave.

In new construction today, there would indeed be a separate circuit
breaker for the microwave, disposal, dishwasher, refrigerator, and
other large, dedicated appliances. Those separate breakers would
either each be wired directly to the appliance or each wired to a
single oulet serving each appliance.

The treadmill is a marginal case. Technically, you could get by
without a dedicated circuit if you were careful not to turn on any
other large loads connected to the same circuit while you were using
the treadmill. So if you had an electic heater plugged into an outlet
connected to the same circuit breaker as the treadmill, you would be
ok as long as you didn't use the heater and treadmill at the same
time.

The circuit breaker is there to limit the maximum power that can be
drawn from all the wiring connected to it. This prevents overloading
the wiring which can cause a fire. Generally, if you are not tripping
any circuit breakers, then you are OK. I say generally, because
circuit breakers are not precision devices. If the overload is large,
they will trip quickly. But if the overload is small they may run for
hours before they trip. This is usually not a problem because there
is enough safety margin to prevent problems from small overloads.

Still, if you know when you use your treadmill that you are going to
want the TV on and all the lights in the garage on, then you may want
to consider having a dedicated circuit installed.

HTH,

Paul