How to Convert 208 Volt to 220 Volt

Three-phase 208-volt electric motors are less expensive and more efficient than 220-volt single-phase motors. For this reason, three-phase motors are common on industrial and restaurant equipment, while similar equipment can be difficult if not impossible to find with a single-phase motor. The difference in nominal voltage rating is small enough to be inconsequential, but the three-phase motor's requirement for a third power supply leg must be met. While there is no way to retain the three-phase motor's efficiency advantage without paying for a dedicated three-phase service line, devices are available to convert a three-phase motor to single-phase operation.

Things You'll Need

  • Rotary phase converter

  • Three-phase fused disconnect

  • Insulated 12-gauge wire

  • Screwdriver

Step 1

Switch off the service panel breaker for the single-phase, 220-volt supply circuit.

Step 2

Connect the black wire of the supply line to the T-1 input terminal of the three-phase disconnect. Connect the red wire to the T-2 input terminal, and connect the bare wire to the ground terminal of the three-phase disconnect.

Step 3

Connect a wire from the T-3 terminal of the phase converter to the T-3 input of the three-phase disconnect. Connect a second wire from the T-2 terminal of the phase converter to the T-2 output terminal of the disconnect. Connect a third wire from the T-1 terminal of the phase converter to the T-1 output terminal of the disconnect.

Step 4

Connect the T-1, T-2 and T-3 wires of the motor to the corresponding output terminals of the disconnect.

Step 5

Connect a ground wire from the chassis ground of the motor to the chassis ground of the phase converter, and thence to the ground connection of the three-phase disconnect.

Warning

Never attempt to work on a live circuit.

Connect the T-1 and T-2 phase converter terminals to the output terminals of the disconnect, never to the input. Otherwise, the phase converter will be energized even when the disconnect is off.

References & Resources