Three Phase Power
This is the best explanation yet about three phase power:
Three Phase Power: The most common type of 3 phase is called 3 phase WYE. This is a
5 wire power system with 3 phases, neutral and ground. The three phases are 120 degrees
out-of-phase with each other, requiring only one Neutral return wire. The shared Neutral
reduces overall wiring costs. Another advantage of 3 phase is the “dual voltage” capability.
A three phase connection can provide 120 volts by connecting phase to neutral or 208 volts
by connecting phase to phase. This is ideal for a system where equipment operating at
both voltages is required. One power cable and receptacle can replace three single-phase
connections. One 3 phase 20 amp connection is equal to 60 amps of single-phase power.
3 phase power is ideal for power intensive environments such as data centers or large ATE
(Automated Test Equipment) systems.
http://www.pulizzi.com/store/2007_Catalog/2007_Catalog_Full.pdf
Next Question - How can you utilize 3 phase and how would the wiring be?
First, there are 5 wires - 3 (Phase A, B, and C) are hot (208V), a Neutral, and a Ground
If you want three 120 volt circuits you connect each phase to Neutral.
Phase A to Neutral
Phase B to Neutral
Phase C to Neutral
If you want three 208 volt circuits you connect each phase to another phase.
Phase A to Phase B
Phase B to Phase C
Phase C to Phase A
Neutral is not used for creating 3 phase 208 circuits. In either 120 or 208 cases the Ground wire is there purely for safety and does not carry any voltage.
Comments
First, there are 5 wires - 3 (Phase A, B, and C) are hot (208V), a Neutral, and a Ground
I'm thinking that A,B and C are 120v and the three different combinations of hot-hot are the ways you get three separate 208v circuits and the a,b,c -> neutral are the three 120v circuits.
At least that's how my reality would make it so.
Now whether or not that bears any resemblence to what's really going on here, I guess time will tell :)
There is a good explanation at http://science.howstuffworks.com/power3.htm
Essentially it doesn't matter what voltage each of the hots are. However whatever the voltage is, will be the maximum voltage circuit you can make. So in your question you state each of the hots is 120, you would get 3 120 circuits or 3 cut by a bunch of mysterious math (citation needed) and have 3 much less than 120v circuits. In my example, the hots are 208v.
From that link above, they have a cool picture of thre phase power leaving the power plant and they state that voltage can be anywhere from 155,000 to 765,000 volts! That's a lot of voltage.
Heh...I think I am going to politely disagree :)
I found this:
ref: Powering 1 Phase Loads on 3 Phase Power
So, 1.73 * 120 = 207.6.
I think the voltage of the hot's matter :)