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I have a single phase 230 volt motor. I am getting 230 volts (115 at each terminal marked with the red line in the image below). The motor is not drawing any amperage at all and is making no noise at all. The centrifugal switch looks okay. Can it be the start capacitor? I was under the impression that if the start capacitor was bad it would still pull amperage. What can I test next to help determine why the voltage is not ultimately getting to the the windings?

enter image description here

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    \$\begingroup\$ Is there a broken wire somewhere or even a thermal cutout - you may be lucky some are re-settable others need replacing... \$\endgroup\$ – Solar Mike Oct 8 '17 at 13:09
  • \$\begingroup\$ I'm not sure. I'll try to find an electrical diagram for this motor online somewhere. \$\endgroup\$ – Bill Greer Oct 8 '17 at 13:17
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A single phase AC motor has two windings. the main winding and the secondary winding to help starting the motor. The auxiliary winding is switched in series with a capacitor and possibly a centrifugal switch.

In your case the main winding can be found by measuring the resistance (relatively low). The auxiliary winding can be found in the same way and should have a higher resistance. If you have more connections a thermal protection might be there also and could be defective or needed a reset.

Once both windings are found you have to make sure that the auxiliary winding is in series with the start capacitor and the centrifugal switch. The centrifugal switch is normally closed and opens when the motor speed is high enough to switch of the auxiliary winding.

When connecting the motor back to the mains there should be a current flowing through the main winding and the motor should start to run if the auxiliary circuit is also ok.

So first verify the all the connections and make sure they are ok. From there you should be able to proceed.

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If it's new, never has run before, you might have both the terminals you indicated connected to the same phase You say that both are at 115, as they should be. Have you measured 230 volts between them?

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  • \$\begingroup\$ Thanks John. The motor ran just fine a couple of weeks ago. \$\endgroup\$ – Bill Greer Oct 9 '17 at 12:32
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    \$\begingroup\$ But along those same lines, if your 230V comes from two separate breakers that do NOT have a common trip, one breaker can trip and the other one stays energized. You will read 115V on both terminals because inside of the motor, they are common to each other and you are reading the SAME 115V circuit right through the motor windings themselves. With the motor not spinning, there is no impedance, only the resistance of the wire and that's very very low. So again, read the voltage BETWEEN the two terminals, not one at a time. If it reads zero or some very low value, that's the problem. \$\endgroup\$ – JRaef Oct 9 '17 at 20:11

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