DIYbanter - View Single Post - Load capacity of 200-amp panel

Doug Miller

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

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.

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?

Now fully load the other leg too.