The label attached to the motor

I have a bit of a problem correctly wiring up the motor on a piece of industrial equipment that was ordered from China.

When ordering I was told that it would run off of a three phase supply. I've attached a picture showing the label with the wiring diagrams (supposedly for clockwise and anticlockwise operation) attached to the motor.

The label shows two wiring configurations. It was wired up in the first (clockwise) configuration when it arrived. Both of the configurations seem to expect a single phase supply and use two external capacitors.

The second one quite clearly just shorts the supply. The first one is less obviously stupid, but does not look like any motor wiring scheme I have seen before. But when i connected it up, the motor ran for a few seconds before one of the capacitors (rated for 450 V/AC) started smoking and the breaker tripped.

Can any one explain whats going on here and maybe give me some advice on how to wire it up correctly? Any help would be greatly appreciated!

  • 2
    \$\begingroup\$ Anyone else had any bad experiences buying stuff from China? \$\endgroup\$
    – Andy aka
    Feb 27, 2017 at 11:22
  • \$\begingroup\$ 3phase motors can be run on 1phase using some capacitors (with lower efficiency), I think, the manufaturer put the 1phase schema for those, who does not have 3 phase. Anyway I would try to measure resistance on connectors, maybe it is 3phase motor after all and can be used with 3phase naturally. \$\endgroup\$
    – gilhad
    Feb 27, 2017 at 12:29

1 Answer 1


It is a single-phase motor. Any single-phase motor can be run from a 3-phase supply of the proper voltage. Just connect it to any two phases. Are you sure that you connected capacitors of the proper microfarad value to the proper terminals? Are the capacitors rated for motor-start and motor run duty?

The diagram below shows what I think are the internal winding and starting switch connections. C2 must be the starting capacitor. It is not shown to be connected to the power connections, therefore it must be connected to an internal component that disconnects it after the motor reaches full speed after the power is switched on. Since the stating capacitor has a high capacitance, it allows a high current in the start winding. It is designed to carry the high current for only a about second or two. If it remains connected, it and the start winding will overheat and fail. C2, the start capacitor, should be the 250 uF capacitor and C1, the run capacitor, should be the 50 uF capacitor.

The reversing links change the polarity of the start winding with respect to the run winding. The connection diagram should show the links in only one position, not both at the same time. The motor must have the direction selection changed only when it is unpowered and not turning.

enter image description here

  • \$\begingroup\$ The capacitors used conformed to the capacitor values and rating on the label: C1 (which failed) was 250uF 450V/AC, C2 was 50uF 450V/AC (so has a rating higher than required, but I don't see how that would do any harm). \$\endgroup\$
    – Daniel
    Mar 1, 2017 at 14:02
  • \$\begingroup\$ The 250uF capacitor would be the motor-start capacitor. It is possible that the centrifugal switch or other means of disconnecting the capacitor at full speed failed to open. Did the machine seem to come up to full speed quickly when started? Is this new equipment or used? It seems likely the manufacturer is not competent. The connection diagram is an indication of that. \$\endgroup\$
    – user80875
    Mar 1, 2017 at 15:01
  • \$\begingroup\$ I think the problem is that C1 is the run capacitor and should be 50 uF and C2 is the start capacitor and should be 250 uF. I will post an answer with a diagram to try to explain what I think is going on. \$\endgroup\$
    – user80875
    Mar 1, 2017 at 18:00
  • \$\begingroup\$ I do have a 240V 16A single phase socket available, so I don't have to run it off 2 phases of the 3 phase supply. Thanks a lot for your detailed reply. This has been incredibly helpful. I will try wiring the motor up with the capacitors reversed as soon as the replacement cap arrives. \$\endgroup\$
    – Daniel
    Mar 2, 2017 at 13:15

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