RB wrote:

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?


by code, you are to only connect the neutral to the ground electron
point in the Breaker box and not at any other point.
in 4 wire single phase, a forth wire (ground wire) is used many times
to connect the appliance case at the end point, also you can legally
have this ground reconnect to some other remote ground points but never
reconnect the neutral to any ground other than what is in the breaker
box where the main ground electrode comes in.

the same applies to equipment grounds where is you have a neutral
wire (white) running around in the cabinet, only at one point will that
neutral be connected to the cabinet ground using no smaller than a 10-32
stud how ever, multiple cabinet (case) grounds can be connected all over
the place in side etc..
kind of strange i know but that is the way it is.
i have seen in some cases in equipment panels where the neutral side
of the 120 control source never see's a case ground.! oh well!


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