"Jane" wrote in message
...
Thanks very much for your explanation. I don't quite grasp the
mechanics though. The electrician says that a 100amp panel is really
like a 180 amp panel,(b/c of the two legs which you brought up) but I
don't understand how the circuits utilize the two legs to make an
electrican say that. It seems to fly in the face of the basic advice
of needing a circuit breaker for: garbage disposal, microwave,
desktop, etc... which all adds up to a 100amp panel very fast. If I go
by the advice in the book, I would get a 150amp panel to satisfy all
the equations of load, etc. for the house, yet he tells me the 100 amp
is like a 180 and I'll never trip it even with everything on. And he's
probably right b/c of the "two-legs."


I'm going to search the Web some more for something to read that will
enlighten me. If anyone has a link to offer, I'm all ears. (eyes?)


Yeah, when you know this stuff well, you forget how to explain things to
people who've never looked inside a panel before. Try this link:

http://www.homewiringandmore.com/hom...ng/meter/100as
ubpanel.jpg

This is a 100A panel without a main breaker. The incoming 100A feed comes in
on the red and blue wires (100A available from each). There is 240V between
the red and blue feed wires, and 120 between either the red or blue and the
white feed wire. There are three single pole breakers in this panel, and
lets say they are 20A each. The bottom two breakers get their current from
the incoming red feed wire. If both those circuits are on and using their
full rating, 40A will be sucked off that red feed wire.The higher breaker on
the rights gets it current from the blue feed wire. This could suck 20A from
the blue wire irrespective of what the bottom two breakers are doing. Put in
another breaker on the right side above the two that are there, and it will
get its current from the red feed wire making the total potential draw from
the red 60A. Put in another above that one, and the blue feed could be
loaded to 40A and the red line to 60A. This is 100A, but you still have 40
more available on the red and 60 more available on the blue.

So a 20A breaker doesn't utilize both legs, it is on one or the other. The
layout of the panel makes it such that a column of breakers alternates
between the red feed and blue feed wires. So as long as you're not putting
your breakers in just every other row, you'll be able to suck current from
both incoming lines. This means you effectively have 200A available if
you're only using single breakers.

A 240V double pole breaker, like you'd use for a water heater, range, or
dryer, sucks it current from both lines. So a clothes dryer rated at 25A at
240V would allow only 75 amps to be available on the red and blue legs to
serve your 120V loads (which really means 150 total amps since there are two
legs to choose from on 120V loads).

--
Mark
Kent, WA