The pool pump is driven by a dual voltage single phase motor (115/220VAC) with a 125VAC start capacitor (the motor is set-up for 220VAC; 220V 1P supply.) The motor is started by a 220VAC magnetic contactor (DOL,) but when the start button is pushed the contactor coil won't energize and the contact engages and disengages at rapid pace. I measured the voltage across the contactor coil terminals and it read 140V. No wonder the coil won't energize. Is the drop in voltage caused by the start 125VAC capacitor? I think it takes a few seconds for the motor's start circuit to disconnect thus preventing the contactor coil from energizing.

Edit: Measured both run and start capacitors and both read the same capacitance as printed.

Also measured the resistance across the contactor coil and it is ok as per manufacturer's data.

  • \$\begingroup\$ How old is it? Starting caps fail (are considered a consumable) every 3-5years (lucky ones can get 10years). They usually cost about $15 to replace. \$\endgroup\$
    – Aaron
    Mar 24, 2022 at 3:17
  • \$\begingroup\$ It's a new pump. I have measured both the start & run capacitors & both read the same farads as printed. \$\endgroup\$
    – Civi
    Mar 24, 2022 at 3:22

1 Answer 1


Is the 125VAC start capacitor preventing 220VAC contactor coil to energize?

No, it's not.

The contactor coil is in the control circuit and the capacitors in the motor circuit.

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Hence contactor functioning would not be affected by the capacitors.

Contactor chatter could occur should

  1. the contactor be of the DC type instead of AC

  2. the shading ring in the armature of the AC contactor be damaged.

By the way, capacitor voltage rating of 125 V is quite low for 220 V operation.

250 V would be more appropriate.


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