"RB" wrote in message
.. .
For single phase, 220v ac: what is the difference between 3 and 4 wire
systems?

Most 220 comes into houses with three wires. Two insulated, and one bare.
This implies to me that the bare one is also a ground, as well as the 220v
neutral.

I also observe portable generator to house setups using 4 conductor cable.
Why the difference? Are the 4 conductor setups simply using separate
neutral and ground? If so, is there any practical and/or safety reason to
separate the neutral from ground lead?



In North America it's 120-0-120 which comes from a center tapped
transformer. The center tap is grounded and is also connected to the bare
wire which connects to both the ground and neutral busses in the panel. From
either hot to ground/neutral is 120v, between the two hots is 240v.