A burnt-out three-phase motor is usually recognised by three signs: a sharp smell of burnt varnish from the frame, protection that trips as soon as the motor is energised, and, with the power off, a clear difference between the three windings or leakage between a winding and the frame. The final verdict comes from measurement; the smell alone is not enough proof.

Signs you can see from outside

  • Darkened terminals, melted cable insulation or soot marks when the terminal box is opened.
  • Darkened, browned winding ends visible through the ventilation openings.
  • The motor humming without turning, making irregular noise or overheating very quickly.
  • The overload relay, motor protection breaker or residual current device tripping the moment the motor is switched on.

Check order

  1. First isolate the power at the panel, lock the switch and hang a warning tag on it. Have the measurements done by a qualified electrician.
  2. Remove the links in the terminal box and measure each phase winding (U1-U2, V1-V2, W1-W2) separately. In a sound motor the three values are very close to each other.
  3. Have the insulation between each winding and the frame tested with a megger. A multimeter is not sensitive enough for this; the method is in the question on insulation resistance testing.
  4. If the readings are clean, look for the problem outside the motor: cable, contactor contacts, fuses and phase voltages.

Burnout is a result; a new motor fitted without finding the cause may suffer the same fate. We have collected the link between symptoms and causes in our article on motor faults, symptoms and causes. If the motor has to be replaced, the buy electric motors section lists models by power and speed. Send a nameplate photo of the burnt motor and a photo of the inside of its terminal box on WhatsApp; we will identify the equivalent new motor for you.