On my AC motor nameplate, it says V230/400 (delta/star). I imagine this means that it is compatible with both voltages, but what allows it to do this? How will the performance change for each?

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    \$\begingroup\$ A quick Google search revealed your answer: It's for 2 speed. \$\endgroup\$
    – user69821
    Jul 10, 2015 at 12:54
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    \$\begingroup\$ Probably not 2 speed. In Star connection, 400 V phase-phase is about 230V Phase-Neutral. You will have to change internal connections (probably links under the connection cover) to switch between voltages. \$\endgroup\$
    – user16324
    Jul 10, 2015 at 13:30
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    \$\begingroup\$ @BrianDrummond: No connection changes are required. Regardless of whether the motor is wired as star or delta internally, it is compatible with a 230V star feed or a 400V delta feed, since they're equivalent. \$\endgroup\$
    – Dave Tweed
    Jul 10, 2015 at 14:16
  • \$\begingroup\$ @Dave Tweed, I read that as "230V when wired as Delta, 400V when wired as Star". If the nameplate really meant 230V star, 400V delta as you suggest, then it is written badly to create confusion... \$\endgroup\$
    – user16324
    Jul 10, 2015 at 15:04
  • \$\begingroup\$ @BrianDrummond: Actually, the answer by kabZX is probably closer to the mark. I guess maybe that's what you were trying to say -- I just misunderstood. \$\endgroup\$
    – Dave Tweed
    Jul 10, 2015 at 15:14

1 Answer 1


(Assuming you are talking about an induction motor) Such a motor will have six terminals - i.e. start and end points of all three windings available, which you should connect as star or delta. The terminals are arranged to allow you to do this easily.

The motor is rated to tolerate 230V RMS across points U1-W1, U2-W2 and U3-W3. If you connect it in in star connection you can have V(L1-L3) = 230*sqrt(3) = 400V rms.

In delta mode you can only have V(L1-L3)=230V, so you probably shouldn't directly connect it to the 440V 3-phase supply in delta mode.

Star-Delta config for motor

  • \$\begingroup\$ Wow, the first real application of a Y to T resistor configuration that I've seen in the wild. Or Y and T resistor configurations, anyway. \$\endgroup\$
    – jfa
    Jul 10, 2015 at 18:06

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