There is no single figure that fits every motor: the microfarad (µF) value of a single-phase motor capacitor is calculated by the manufacturer together with the auxiliary winding. That is why the value on the motor nameplate prevails; if the nameplate is unreadable, the value printed on the old capacitor is the reference.

Why is µF specific to the motor?

The capacitor shifts the current in the auxiliary winding relative to the main winding and so creates the rotating field. The size of this shift depends on the wire cross-section, the number of turns and the motor power. Two different motors of the same kW rating may need different capacitors. "So many µF per kW" rules found online are only rough estimates; a wrong value heats the winding.

Checklist for the replacement

  1. Capacitance: Exactly the µF value on the nameplate or the old capacitor.
  2. Voltage: Equal to or higher than the old part's rating; a lower-voltage capacitor fails quickly.
  3. Type: A start capacitor is never fitted in place of a permanently connected run capacitor, nor the other way round.
  4. Body and terminals: A size that fits the terminal box or cover, with suitable connection terminals.

Dual-capacitor motors carry two separate values; read each one separately and do not mix them up. Before touching a capacitor, switch off the power and make sure it is discharged; we recommend having the replacement done by a qualified electrician.

For the capacitor's function and direction of rotation, see the question what does the capacitor do in a single-phase motor. If you are thinking of renewing the motor, review the models on the single-phase 220 V electric motor page; for current prices see our article on single-phase motor prices. If you send the nameplate photo on WhatsApp, the capacitor value is confirmed with the order.