Chris,
This also brings up the subject of harmonics created by some loads(computer switching power supplies)that do not get canceled in the neutral because there is no equal and opposite phase(180deg) current from the other side.
There are no documented reports of excessive neutral current in the neutral of 120/240 volt single phase systems with harmonic loads. These currents, do for the most part, cancel in 120/240 single phase systems. The only neutral problems caused by nonlinear loads are on 120/208 and 277/480 volt 3 phase wye systems. As a matter of fact the easiest and cheapest way to eliminate the neutral problems caused by nonlinear loads is to use 120/240 single phase systems in place of the more commonly used 120/208 volt wye systems.
Don
