Can 1 phase be used with 3 phase?

Answer 1

If you have a 208Y/120 volt 3 phase system, you can use any one of the three phases (hot or ungrounded conductor) with the neutral for 120 volt load or you can use any two phases of the three phase for a single phase 208 volt load.

If you have a 120/240 volt 3 phase system, you can use any two phases of the three phase for a single phase 240 volt load or you can use either the A phase or C phase with the neutral for a 120 volt load. You can not use the B phase with a neutral (you would have 208 Volts!).

Answer 2

I am assuming we are taking 240 volt single phase to 240 volt 3 phase, it can be done. Two ways, you can use a variable frequency drive, this drive would be sized at twice the load. So if you have a 5 hp 3ph motor you would need a 10 hp VFD. You can also use a rotary phase converter, it would also be sized at twice your attached load. A rotary phase converter can be built from a standard 3 phase motor or there are companies who manufactuer them.

Answer 3

Single phase can not be converted to three phase without a cost being involved. If the conversion is for a motor that scenario can be accomplished. Depending on the amount of money you want to spend to make this happen there is a device on the market called a VFD ( Variable Frequency Drive). On the three phase input terminals you apply your single phase voltage. On the output terminals you connect your three phase motor. When run in this configuration there is an internal switch that has to be changed to let the VFD know that it should be looking for only two lines on the input to be hot. Other wise the VFD thinks that there is a line loss on the three phase input terminals and the unit will not start.