On Oct 24, 2:17*pm, (Doug Miller) wrote:
In article , wrote:







Consider this simple circuit analogy which is exactly what you would
have with a balanced load on a 240V service. * *It's a 240V voltage
source powering two 120ohm resistors.

* * * * * * ____________ *240V___________
* * * * * * I * * * * * * * * * * * * * * * * * * * * * * * * I
* * * * * * I * * * * * * * * * * * * * * * * * * * * * * * * I
* * * * * * I * * * * * * * * * * * * * * * * * * * * * * * * I
* * * * * * ---------120ohm---------120ohm---------
* * * * * * a * * * * * * * * * * * b * * * * * * * * * * * c

There is only 1 amp of actual current flowing in the circuit. * Across
each resistor there is 120Volts and 1 amp of current flowing. * *So,
yes you have 1 amp flowing in EACH load, it is supporting two 1 amp
loads, but it's the same physical current flowing through each load.
The "service" is only supplying 1 amp of actual current, not 2.

What voltage do you measure between a and b? Between c and b?

120 Volts
120 Volts



What current do you measure between a and b? Between c and b?

1 amp and it's THE SAME 1 AMP current. It just gets counted twice.
Which once again is my point. There is only 1 amp flowing in the
actual complete circuit, just like there is only a maximum of 200
physical amps flowing in a 200 amp service.

In a house, here's how the same thing happens. I hook a 120Volt
light bulb that draws 1 amp on one hot leg and a 120volt fan that
draws one amp on the other hot leg. The 1 amp current comes in one
leg, goes through the bulb, through the fan and out the other hot
leg. That's still an actual current of only 1 amp, though it runs
through two 1 amp loads. If you want to get techical, since it's AC,
the current direction switches each cycle.

Kapisch?


That's what I meant when I said a 200 amp service cannot supply 400
amps of current.

But it can. 200A at 120V on each leg is a total of 400A at 120V. The two legs
of a residential electrical service are, in effect, two parallel circuits..
200A flowing in each of two parallel circuits is 400A total, not 200A.

They are NOT parallel circuits. That would imply that each has it's
own seperate return path. They do not. The return path is through
the other hot conductor for the balanced part of the load and through
the shared neutral for the unbalanced portion. Again, at any point
in time there is only 200 amps moving through that service going into
the home, which is why it's called a 200 amp service.



Consider a house with only 120V loads, no 240V circuits anywhere, and 200A
service. Suppose that one leg of the service is fully loaded, and the other
leg is unloaded. I think we'd both agree that the power being drawn is 200A at
120V, right?

Yes


Now fully load the other leg too.- Hide quoted text -



And now you have 200 amps flowing from one hot and back on the other
hot. Zero flows through the neutral. Hence, again, it's only a
200 amp total current moving through the service.