Hi,

I've been scratching my head over something. I have a scenario (theoretical) where you can either use 2 wires @ 230V or 3 wires @ 200V 3-ph. The size of the wires is limited by voltage drop, which is the same percentage wise for both cases. According to textbooks and common knowledge, 3-phase is more efficient than just using two wires. But I fail to arrive at this result in this case.

If I put 1A load the 3-ph case I need 1.73/1.15 = 1.5A single phase to get the same power. This means I have to increase the cross sectional area of the conductors by 50% compared to the 3-phase case. But I only need 2 wires instead of 3 and am back at the same amount of copper.

Is there something wrong with my calculations? Wouldn't be the first time...