On 2009-10-24, Doug Miller wrote:

A 200A residential service supplies up to 200A _at 240V_. This is
_exactly_ equivalent to 400A at 120V -- which is precisely what you
have if each leg of the service is fully loaded at 120V.

There are a couple small differences between 400A worth of 120V loads
balanced on the two legs of a 240/120V supply, and 400A of loads on a
120V supply. First, in the former case the biggest 120V load you can
handle (without a transformer) is 200A, while in the latter case you
can handle a 400A 120V load. Second, the voltage drop on the supply
is different. V = I^2 * R, where I is 200A in the first case, and
400A in the second case.

Cheers, Wayne