On Wednesday, July 17, 2013 3:41:15 AM UTC-4, wrote:
My main breaker is 100A at 240 volts. I've always been confused about

this. Does that mean I can use up to 100amps at 240volts, OR up to 200

amps at 120 volts?



Or does is the limit 100amps at either voltage?


Physically there is never more than 100 amps flowing in
the service. However, if the 120V loads are balanced, meaning
there is an equal load on both hot legs, then you can have
100 amps flowing through each of those loads, making it
appear like it's 200 amps at 120V.

For a simplified version, think of a 240V voltage source
connected to two 1.2 ohm resistors that are in series.
There is 100 amps flowing in the circuit, with 120V
appearing across each resistor. So, each of those resistor
loads has 100 amps going through it, with 120V appearing
across each.

For you to get 200 amps at 120V out of your service, 100
amps of load must be on each leg. If you put all the 120V load
on one leg, you'd only get 100 amps. That 100 amps would be
coming in on the one hot and going back on the neutral.
If you put say 70 amps on one leg, 50 amps on the other,
then you'd have the difference, 20 amps, flowing back in the neutral.
But there is never more than 100 amps of total current.