When you go to swap a pump capacitor, the first thing to check is how many terminals it has. A 2-terminal capacitor and a 3-terminal one are wired completely differently, and getting it wrong can stop the motor working or damage it. This guide explains the difference and how to wire safely.
Safety first — and this one is serious
A capacitor holds a dangerous charge even with the power off and the pump unplugged. Before you go near the terminals:
- Isolate power at the breaker.
- Discharge the 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.
- Only then start disconnecting wires.
In New Zealand, fixed mains wiring legally requires a licensed electrician. If your pump is hard-wired into the mains or you’re not confident, use a sparky — it’s both safer and the law.
Photograph the wiring BEFORE you disconnect anything
This is the most important practical tip in this article. Take a clear, well-lit photo (or several) of the existing wiring before you remove a single wire. Capacitor wiring varies between motors, terminals can be unmarked, and once the wires are off it’s easy to forget which went where. A photo turns reassembly from guesswork into a simple match-up. Also note the colour of each wire and which terminal it sat on.
2-terminal: the single run capacitor
A 2-terminal capacitor is a single run capacitor — one capacitor element with two connection points. This is the most common type on smaller single-phase pumps.
- Two wires connect to it, one per terminal.
- On most single run caps the two terminals are interchangeable (no polarity), but always rely on your photo rather than assuming.
- Body codes here are usually CBB60 or CBB65 (film run capacitors).
This is the simplest swap: discharge, photograph, disconnect, fit the matching replacement, reconnect.
3-terminal: the dual-run capacitor
A 3-terminal capacitor is usually a dual-run capacitor — effectively two capacitors in one can, sharing a common terminal. You’ll see this more on larger motors and HVAC-style setups than on basic pumps, but it does appear.
The three terminals are typically marked:
- C — Common
- FAN (or HERM / one of the two windings)
- HERM (hermetic / the other winding)
Each pairing (C–FAN and C–HERM) has its own capacitance value, often different from each other (for example, a “40/5 µF” dual cap). When you read a dual-run cap, you’ll see two values printed.
You cannot substitute a 3-terminal dual cap with a single 2-terminal cap (or vice versa) without rewiring — they’re different circuits. Match terminal count and both values.
Comparison at a glance
| | 2-terminal (single run) | 3-terminal (dual run) | |—|—|—| | Capacitor elements | One | Two in one can | | Terminals | 2 | 3 (C + two outputs) | | Values printed | One µF value | Two µF values (e.g. 40/5) | | Common markings | none, or +/- positions | C, FAN/HERM | | Typical use | Smaller pumps | Larger motors, combined fan+motor |
Terminal connector types
Separate from the terminal count is the connector style — match this too so the wires fit cleanly:
- Spade / lug — flat push-on tabs (often doubled, so several wires can share a terminal).
- Flying lead — wires come pre-attached out of the capacitor; you join them to the motor leads.
- Stud — a threaded post with a nut, common on larger CBB65 cans.
If you’re unsure which body type you have, our guide to CBB60 vs CBB65 vs CD60 covers the common cases.
Reading the values for a correct match
Whether 2 or 3 terminals, the rule on values is the same:
- Read the µF and voltage off your own capacitor (and cross-check the motor nameplate). Don’t guess from a model number.
- The µF must match within about ±5%. On a dual cap, both values must match.
- The voltage rating can be equal or higher (450V is a safe substitute for 370V); never lower.
Need help decoding the print? See how to read a capacitor label.
Step-by-step recap
- Isolate power at the breaker.
- Discharge the capacitor (insulated screwdriver / resistor across terminals).
- Photograph the wiring and note wire colours and positions.
- Disconnect and read the body code, µF, voltage and terminal count.
- Fit a matching replacement (same terminals, µF matched, voltage equal or higher).
- Reconnect using your photo as the reference.
- If hard-wired or unsure, hand this stage to a licensed electrician.
What to do next
Match terminal count, terminal style, µF (exact) and voltage (equal or higher) to your existing part.
- Browse all pump capacitors.
- Use the find-your-capacitor wizard to match by terminals and value.
- Well pump? See the well capacitor range.
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CapacitorsNZ — find your exact capacitor with our wizard, then shop pump capacitors or the well range.
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