Sparkee
Its a little more complex than that.The currents are 120 degrees out of phase in the 2 phase wye system. In a single phase system with 2 hots and a neutral the currents are 180 degrees out of phase and substract in the neutral.
In order to caculate the neutral you must use vectors to arrive at the neutral current.
At 120 volts 1500 w = 12.5 amps at an angle of 0 degrees and 1700 w = 14.2 amps at 120 degrees. To add these together you use trig.
14.2 amps at 120° = 14.2 cos 120° + 14.2 sin 120°. Add the 2 loads together = (-7.1 + 12.5)angle 0 + (12.4)angle 90 which equals
5.4 (ang 0) + 12.5 (ang 90).
The get the magnitude the neutral current =
sqrt(5.4² + 12.5²) 13.5 amps.
Additional info is at
http://www.electrician2.com/electa1/electa3htm.htm
