3 phase only needed if your peak load is more than 10kW or 15kW (i forgot which one), usually household appliances only state max load of a few kW but rarely hit that max load.

Another reason to use 3 phase is for the big 3 phase AC motor like those compressor in a 24kW chiller system.

This post has been edited by Hornsen: Jan 13 2012, 05:47 PM