- Hello World -
What are inside the feed wires? 2 hots @120V each, and a neutral?
The neutral and ground are usually connected at the panel. So
how the electricity figure which way to go, to the neutral, or to
the ground?

- Nehmo -
For simplicity, let's only concern ourselves with _one_ hot (black), the
neutral (white), and the ground (bare or green). Also let's just
consider an instant in the changing Alternating Current (AC) cycle, when
the hot is conventionally-called positive. Electricity of the household
line-current type can only travel in a complete circuit – the circuit
has to form a loop. So if a load, a lamp (a lamp with a metal housing
that is grounded to the ground prong of a 3-prong plug) for example, is
placed between the hot and the neutral (the normal situation), the
electricity goes, from the panel, through the hot, through the lamp,
then back through the neutral back to the panel. The ground wire does
nothing because there is no complete circuit that includes the ground
wire.

But suppose something goes wrong: let's say an insulation-stripped hot
wire inside the lamp now touches the lamp housing, a short. Now when you
turn on the lamp, which allows current to the hot wire, the electricity
goes from the panel, through the hot, through the short to the lamp
housing, through the ground prong of the plug, through the ground wire,
and back to the panel where, since the resistance of the circuit is low
and the current is thus high, the breaker opens. The ground wire served
its purpose.

That's how the electricity knows where to go; it goes only where the
circuit is complete.


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* Nehmo Sergheyev *
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