A burnt winding is not the fault itself but the result of some kind of strain. Before fitting a new motor of the same power, find out what overheated the old one; otherwise the new motor faces the same conditions and soon ends up in the same state.

DRG-801-2 0.75 kW 3000 rpm aluminium frame DRG three-phase motor – what to do after a motor burns out

Clues from a burnt winding

Having the removed motor examined by a rewind shop or qualified electrical staff narrows down the cause. Even darkening of the whole winding usually suggests prolonged overload or poor cooling. If only one or two phase coils are burnt, a defect on the supply side comes to mind. A puncture and mark at a single point may be linked to moisture, contamination or a voltage surge. These readings are not a firm diagnosis; they are pointers.

Points to investigate

  1. Supply: Voltage balance between phases, condition of fuse and contactor contacts, agreement between mains voltage and nameplate voltage.
  2. Protection: Whether the motor protection was chosen for the motor actually installed. Settings depend on the nameplate and on the judgement of qualified staff.
  3. Machine load: Whether product, capacity, pulley or impeller has changed recently; whether the machine turns freely by hand.
  4. Cooling: A blocked fan cover, a layer of dust on the fins, the motor running in hot air inside an enclosed housing.
  5. Starting frequency: The motor stopping and starting very often at short intervals.

Is the same power really right?

If the old motor has been rewound over the years, its label may not reflect its real values. Changes made to the machine may also have left the power short. Increasing power without weighing up current measurement, the machine maker's figure and the type of load together hides the problem but does not solve it. To compare motor current with the nameplate value, the motor current table is a useful guide.

When the new motor arrives

Qualified staff should confirm that the voltage and connection data on the new motor's nameplate suit the control panel, and current should be measured and logged at first start-up. That record becomes a reference point if a problem appears later.

Once the cause has been removed, you can find models of the right power and speed in the three-phase motor shop and compare frame and dimensions with the old motor on the technical drawings page.