On Sat, 31 Aug 2013 06:28:18 -0700 (PDT), TimR
wrote:

On Friday, August 30, 2013 1:54:39 PM UTC-4, wrote:
The US power grid uses "alternating current" (AC). The electrons flow

from positive to negative, then reverse to flow backward from negative to

positive (rising and falling in a sine wave). In the US the current

alternates back and forth like this 60 times a second (60 hz). So

technically, the electricity is flowing in both directions.



True but irrelevant. There is a "source" and a "sink". The breaker

can't tell the difference, so it doesn't know it's being back-fed

(which is the subject under discussion).

Electrons move both directions, and slower than you think.

You would be wrong but that seems to be the norm, here.

But saying electricity is flowing in both directions is misleading.

Uh, you know you can measure voltage drop along a long wire from source to sink, right?

The breaker cannot. It cannot tell where the source or load is. It
doesn't know where the power is coming from or where it's going.