I have sourced an AC variable frequency motor, it came from some sort of excercise equipment.

I would like to find out if it runs, but the wires puzzle me. The wires are:

  1. Black
  2. Red
  3. Yellow
  4. Yellow/green

1, 2 and 3 run together inside a jacket, which is wound around a ferrite ring.

Wire 4 is obviously a ground wire, no mystery there.

But, how should I connect this motor to mains to get it working with minimal amount of smoke produced (if it works in the first place)

The plate on the motor has the following info (these also are not mysterious to me)

  • TYPE YVPP90L -4
  • 3.0HP(MAX 4.5HP)
  • 220V
  • 6.4A
  • 50 HZ (4-100HZ)
  • DUTY S1
  • LW70DB(A)
  • NBCC
  • RoHS
  • CE (the "china export" version)
  • 1
    \$\begingroup\$ Sounds like a normal 3 phase motor. Black/red/yellow is for the three phases. Connect one to each phase and turn it on. If it spins in the wrong direction, switch any of the two phases. Don't forget or skip connecting the grounding (yellow/green) to the ground. \$\endgroup\$
    – KristoferA
    Jun 13, 2021 at 11:16
  • 1
    \$\begingroup\$ Did you try to find a manual for this YVPP 90L-4? Many manufacturers have motors with model 90L-4. \$\endgroup\$
    – Justme
    Jun 13, 2021 at 11:43
  • 1
    \$\begingroup\$ There was probably a VFD in the exercise equipment designed for the job. If you want variable speed, go back and get it, or buy another from a machine tool supplier. \$\endgroup\$
    – user16324
    Jun 13, 2021 at 13:50
  • \$\begingroup\$ Thanks all, was prolly driven by a VFD, but trying to avoid buying one before I know wheter it runs. Gotta keep googling... i have access to 3 phase at home, but kinda hesitant with that. \$\endgroup\$
    – Jpe61
    Jun 13, 2021 at 14:27
  • \$\begingroup\$ The yellow/green wire is the equipment/earth ground. Use a megger and check between that and each of the three remaining leads, you should gt at least 1.3 meg or greater with each combination, if not it is bad. The resistance between any two of the three phases should be about the same. \$\endgroup\$
    – Gil
    Jun 14, 2021 at 3:15

1 Answer 1


But, how should I connect this motor to mains to get it working with minimal amount of smoke produced (if it works in the first place)

Nearly all variable frequency motors are three-phase motors. Unless you have three-phase power available, you can not test it by connecting to phase power. Before testing under power evaluate the motor as follows.

The first step in testing a salvaged motor should not be to connect it to power at all. First Use an ohmmeter to carefully check the resistance between each motor lead and every other lead. Record the resistance values. Also check the resistance between each lead and the motor core. For a three-phase motors, the resistance among the poser leads should be equal. Only the ground lead should show a low resistance to the motor frame.

Turn the shaft by hand to evaluate the condition of the bearings. Also note any resistance to turning that would indicate a permanent magnet rotor. A tendency for the rotor to stop in two or more fixed positions would indicate a permanent-magnet rotor. Attach an AC voltmeter between any two motor leads. If the the motor produces voltage when turned by hand, it is a permanent-magnet motor.

If the motor is a three-phase motor, you could test it using a Steinmetz connection. That is described in the answers to the following EESE questions and perhaps others.

3 phase motor running on single phase using steinmetz delta connection

Identifying direction of rotation for a three phase motor, without applying three-phase power

  • 1
    \$\begingroup\$ can probably get it running on single phase using a run capacitor. \$\endgroup\$ Jun 13, 2021 at 12:15
  • \$\begingroup\$ Thanks, mechanically it seems perfectly intact. I'll check stuff out with a multimeter. \$\endgroup\$
    – Jpe61
    Jun 13, 2021 at 14:31
  • \$\begingroup\$ Oh, the placard says 220V, if this was 3-phase, should it read 380 🤔 \$\endgroup\$
    – Jpe61
    Jun 13, 2021 at 18:03
  • \$\begingroup\$ @Jpe61 220 volt three-phase isn't unheard of, especially for a motor designed to run from a VFD that can apply whatever voltage you want. It's also quite close to 208 volt three-phase, which is common in North America. \$\endgroup\$
    – Hearth
    Jun 13, 2021 at 18:20

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