Requiring single-phase power to run lights and appliances in buildings supplied with three-phase power is quite common. Fortunately, the conversion is easy to do, only requiring the proper connection of wires. By connecting any one of the three phases with the neutral or ground in a 208-volt, three-phase system, a single-phase, 120-volt circuit is isolated.
Turn off the main breaker; it should be labelled.
Remove the cover from the electrical panel.
Install a single-pole breaker in the breaker panel.
Hook the "hot" (black) wire of the single-phase circuit to the screw terminal on the breaker.
Hook the neutral wire (white) to the neutral bar in the electrical panel.
Connect the ground wire (bare) to the ground bar in the electrical panel.
Reinstall the panel cover, and turn on the main breaker and the new single-pole breaker.
Using the voltmeter, test the new circuit for proper operation.
Never work on a live electrical circuit.