I'm reading the book Basic Electricity from Milton Gussow and there's a problem that is driving me crazy, I'm not able to get the result. Can anyone provide me with a guideline to resolve it?
This needs phasors because your motors take a little inductive currents and the lamps act as resistors. The motors are Y-loads but the lamps are a D-load, which cause harmful interline currents. Fortunately the lamp banks are identical, so the equivalent resistive Y-load exists. Find it and add the single line currents as phasors. Note that delta to Y transform is not a must, it only makes the number of needed phasors a little smaller.