"John J.Turley" writes:

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.

One exception (possibly more) is Norway, where they use 230V three
phase, but one of the phase leads are at 0V potential. All the 230V
"single phase" outlets are connected to two phases.

Norway uses 4 prongs in their three phase connectors, while the rest
of Europe use 5 prongs, thre phases, neutral and ground.


The generator you mentioned most likely was a 3-Phase output.

Thomas