Pump capacitor wiring: 2-terminal vs 3-terminal

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:

1. Isolate power at the breaker.
2. 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.
3. 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

1. Isolate power at the breaker.
2. Discharge the capacitor (insulated screwdriver / resistor across terminals).
3. Photograph the wiring and note wire colours and positions.
4. Disconnect and read the body code, µF, voltage and terminal count.
5. Fit a matching replacement (same terminals, µF matched, voltage equal or higher).
6. Reconnect using your photo as the reference.
7. 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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