When you go to replace a pump capacitor, the first thing to sort out is whether it’s a run capacitor or a start capacitor. They do different jobs, look different, and aren’t interchangeable. Fit the wrong one and the motor won’t run properly — or won’t run at all.
The quick difference
- Run capacitor: stays in the circuit the whole time the motor runs. It improves efficiency and keeps the motor turning smoothly. It’s a film capacitor, marked CBB60 or CBB65, usually a smaller µF (tens of microfarads) at a high voltage like 400–450V.
- Start capacitor: only in the circuit for the first second or two to give the motor a strong kick to get spinning, then it’s switched out (by a centrifugal switch or relay). It’s an electrolytic capacitor, marked CD60, usually a much larger µF (often into the hundreds) at a lower voltage like 250V.
A simple way to remember it: run = always on, small, film (CBB); start = brief, big, electrolytic (CD).
How to tell which your pump uses
Most single-phase pump motors fall into one of these layouts:
- PSC (permanent-split capacitor): one run capacitor, always in circuit. Common on pool pumps and many pressure pumps. Quiet and efficient, but lower starting torque.
- CSIR (capacitor-start, induction-run): one start capacitor that drops out once spinning. Strong starting torque, used where the pump starts under load.
- CSCR (capacitor-start, capacitor-run): two capacitors — a start and a run. You’ll see both a CD60 and a CBB-type can.
To find out what you have:
- Look at the motor nameplate — it often lists the capacitor µF and voltage, sometimes both start and run values.
- First isolate power at the breaker and discharge the capacitors (see “Safety before you open it up” below). Then open the terminal cover, count the capacitors, and read their body codes.
- A single small film can = run only. A big electrolytic can = start. Both present = start-and-run.
Safety before you open it up
A capacitor holds a dangerous charge even when the pump is off and unplugged.
- Isolate the power at the breaker first.
- Discharge each capacitor by bridging its terminals with a bleed resistor (around 10–20 kΩ, 5 W) or a proper capacitor discharge tool — a bare insulated-handle screwdriver across the terminals also drains it but sparks violently and can pit the terminals, so use that only as a last resort before touching them.
- Start capacitors in particular can store a hefty charge — treat them with respect.
- In NZ, fixed mains wiring is work for a licensed electrician. If the pump is hard-wired or you’re unsure, use one.
Don’t guess the value — read it off your part
Whichever type you have, match the µF and voltage to your own capacitor or the motor nameplate. Don’t pick a number based on the pump model alone. The wrong capacitance changes the motor’s torque and current, runs it hot, and can damage the windings.
When buying:
- Keep the µF the same.
- Voltage can be equal or higher than the original.
- Match the type and body code — a CBB60/CBB65 run cap is not a substitute for a CD60 start cap, or vice versa.
Replacing both?
On a start-and-run motor it’s worth checking both capacitors while you’re in there — they age, and a tired run cap can mask itself as a starting fault. Not sure what you’re looking at? Our pump capacitors guide breaks down every marking.
Get the right capacitor
Read your label, then let us match the type and value. Use the find your capacitor wizard, or browse pool pump capacitors.
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