How to Wire a VFD

By Yin on 15th Mar 2016

How to Wire a VFD


STEP 1: Make sure everything is correctly sized and accounted for

  • Look at the nameplate on your motor and make sure your VFD is sized correctly.
  • How many full load amps does your motor draw?
  • Is your VFD rated for the amount of amps your motor draws?
  • How many volts does your motor require (460V or 230V)?

STEP 2: Make sure you have a properly-sized circuit breaker rated for your amps and VFD

  • Locate your breaker panel.
  • Remove the dead front and the panel cover.
  • Install your 3 pole amp rated, volt rated, circuit breaker.
  • If you can kill power to the breaker panel before you work inside it, we recommend you do so. If you are unable to do so, make sure you wear the proper safety equipment (leather gloves, safety glasses, arch fault gear, etc.).

STEP 3: Run Wires - (3) power wires and (1) ground wire from your breaker panel to your VFD

  • Make sure your power wire is rated for the Full Load Amps (14 gauge wire up to 15 amps, 12 gauge wire up to 20 amps, 10 gauge wire up to 30 amps, 8 gauge wire up to 40 amps, 6 gauge wire up to 50 amps, 4 gauge wire up to 70 amps, 2 gauge wire up to 100 amps, and so on).
  • If your power wires are #6 up to #2, your ground wire can be #10. For power wires larger than #2, see chart for proper ground wire sizing.
  • Use appropriate wiring method in determining your raceway for wires. Some possible options are: EMT Conduit, Rigid Conduit, Flexible metal conduit (Flex), Metal Clad Cable (MC), NMB Cable (Romex), etc.

STEP 4: Run wires from VFD to motor

  • Use the same gauge wires as you did from the circuit breaker to the VFD.
  • Use proper raceway as you see fit.
  • Land wires in conduit box on motor.

STEP 5: Make-up wires in your motor

  • Use the wiring diagram on your motor to determine the correct wiring method.
  • Most 3 phase motors are dual-voltage, meaning they will accept 480/460 volts or 240/208 VAC.
  • The way you make up the motor will be dependent upon the voltage. Be sure to make it up correctly depending on the amount of voltage you are providing.
  • Use wire nuts to tie your power wires to the proper wires as shown on the motor name plate.
  • Pull on wire nuts to make sure the wires are spliced correctly and are tight. If a wire slips out of the wire nut you know you have a problem and need to redo it.
  • Fasten conduit box cover to motor.

STEP 6: Terminate wires to your VFD

  • Terminate your load wires (wires going to the motor) to the terminals U, V, W.
  • Terminate your line wires (wires coming from the circuit breaker) to terminals R/L1, S/L2, T/L3.
  • If you’d like, you can use crimp terminals. You can also just put a small hook shape in your stripped wire and land it under the screws.
  • Land your ground wires under the green ground screw.

STEP 7: Terminate your wires to your circuit breaker in your panel

  • Land your 3 power wires to the circuit breaker.
  • Land your ground wire to the ground bus bar.
  • Put the dead front and panel cover back on.

STEP 8: Start up

  • Turn the circuit breaker on.
  • Program your VFD to your preferred parameters (See also "Programming Your VFD).
  • Use your preferred starting method (e.g., start/stop buttons, Keypad on VFD) to start the motor.
  • Enjoy the speed control that is now possible with your Mitsubishi VFD.