One simplified way to look at 3ø versus 1ø system is to compare the voltage relationships of 3-wire circuits. [For illustration, ignore voltages with respect to ground.] In a 120/240V 1ø 3-wire arrangement, you can identify each wire, as for instance “A” – “N” – “C” where 120V can be measured A-N and N-C, and the arithmetic sum of 240V from C-A. This is the alternating-current version of what Thomas Edison’s DC generators originally provided for his neighborhoods of electric lights.
In a 240V 3ø 3-wire configuration, each wire is identified as “A” – “B” – “C”, where A – B is 240V, B – C is 240V, and also {note a major difference} C – A is 240V, which is not the sum of the shorter lines like in the 1ø case.
This ingenious arrangement looks simple but has major advantages—it turns out 3ø alternating current is a much more efficient way to get power from one point to another. Visualize 120/240V 1ø 3-wire voltages as two short lines of the same length placed end-to-end. Then, visualize 240V 3ø 3-wire as three lines, but placed end-to-end they make a “loop” or equilateral triangle. The simplified but real-world voltages: A – B is 240V, B – C is 240V, and C – A is 240V for the 3ø system.
For equal current {for instance 100 amperes} and voltage {240 volts} the power delivered in a 3-wire, 120/240V 1ø circuit is 24,000 watts. For effectively the same 3 wires, 100 amperes and 240 volts, the power delivered in a 3-wire 240V 3ø circuit is 41,500 watts. This is a very simplified example, but a valid comparison.
[This message has been edited by Bjarney (edited 07-20-2003).]
