Three-phase systems are prevalent throughout power distribution systems. Each system include 3 separate lines where each line carries the same voltage, which is called the phase voltage. This also means the voltage measured between any two phase conductors will be equal. However, the voltage between any phase voltage and neutral is called the "line voltage." The line voltage is less than the phase voltage by a factor of square root of three or 1.732. For example, if the phase voltage is 208 volts, measured from phase to phase, then the line voltage is 120-volts (208/1.732), measured from any phase conductor to neutral.

Power down the 208 V 3-phase power distribution system. Put on electrical safety glove and observe all electrical safety precautions.

Locate and identify the phase conductor lines on the 208-volt 3-phase system. Each line will have a phase voltage of 208 volts.

Locate and identify the ground or neutral terminal of the 208-volt 3-phase system.

Connect the input terminals of your circuit between any phase conductor and the neutral terminal of the system. This connection point will deliver 120-volts to your circuit.