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Replacement Start/ Run Capacitors

Replacement Start/ Run Capacitors

Replacement start/run capacitors for most common makes of centrifugal pumps.

In single phase electric motors, the run winding is not capable of starting the motor. To start the motor, a secondary start winding uses a starting capacitor to introduce a rotating electric field. This rotating field is not constant, but is sufficient to start the motor spinning. When the motor reaches operating speed, the capacitor shifts to the run winding to control the speed of the motor.

A faulty run capacitor often becomes swollen, with the sides or ends bowed or bulged out. When this happens the motor will ‘buzz’ but not start.

Causes of start capacitor failure

The most common causes of capacitor failure in single phase pumps are severe voltage irregularities (voltage drop or surge) from the power supply or from overheating in a pump with a blocked impeller or seized rotor.

Over long periods of use, the capacitance of the capacitor deteriorates. As a result the motor may fail to start or run at full power.

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Delivery Costs

Delivery Map


Zone 1 England, Wales & Southern Scotland Under £100 Over £100
Standard 2/3 working days


Express Next working day


Premium Next working day (before 13.00)


Zone 2 Scottish Highlands & Islands, Northern Ireland, Isle of Man, Scilly & Channel Isles Under £100 Over £100
Standard 2/3 working days


Zone 3 Republic of Ireland Under £100 Over £100
Standard 3/5 working days




Orders must be placed before 14.00 for next day and premium next day delivery. 


Exporting Internationally

We offer a first class worldwide export service. Please contact us here for a price.
Model SKU Price ex-VAT Qty
10µF CAPACITOR - 150 MM LEADS 3851-000 £14.00
12µF CAPACITOR - 150MM LEADS 3851-001 £16.00
16µF CAPACITOR - 150MM LEADS 3851-002 £18.00
20µF CAPACITOR - 150MM LEADS 3851-003 £20.00
31.5µF CAPACITOR - 150MM LEADS 3851-004 £22.00
40µF CAPACITOR - 150MM LEADS 3851-005 £24.00
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Whisper Pumps Ltd, Leen Court, Boughton, Newark, Nottinghamshire, NG22 9ZD