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?


No one is mentioning a 4-wire system dealing with 3-phase power (Phase
A,B,C + Neutral), where single-phase is available from a neutral
connected from the WYE configured source (generator, transformers,
utility) to any Phase or A to B; A to C; B to C. In countries outside of
the U.S., with 220 VAC single-phase appliances, the system is a 380/220
volt 3-phase 4-wire system. You would have 380 volts single phase
between any two phase wires, or 220 volts from any phase wire to the
neutral. The U.S. equivalent is the 208/120v 3-phase 4-wire system for
small-medium commercial use. Motors rated 208 vac 3-PH (i.e. air
conditioners) could be used and lighting etc. on the 120 VAC from any
leg to the neutral.
The generator you mentioned most likely was a 3-Phase output.