Glenn,
The harmonic problem with the neutral is made even worse when the system is feed from two hots and the grounded conductor of a 208/120 wye system. Not only do the harmonic currents add in the grounded conductor, the normal neutral currents do not cancel in this arrangement. The neutral is aways a current carrying conductor in this system. The neutral conductor current will always be at least equal to the highest hot conductor current. Then you have to add for the harmonic currents.
Don
