Capacitor Wiring Diagram

Capacitor Wiring Diagram — interactive diagram. Open it in the editor to customise components and wiring.

This is a free printable capacitor wiring diagram: download the diagram as SVG or open it and print to paper or PDF.

A capacitor wiring diagram shows how a capacitor is connected in series or parallel with a load — motor start winding, power factor correction bank, or electronic filter circuit — to achieve a specific electrical function.

A capacitor is a passive two-terminal electrical component that stores energy in an electric field by accumulating charge on two conductive plates separated by a dielectric (insulating) material. The stored energy releases back into the circuit when the voltage across the capacitor decreases. The relationship between charge, capacitance, and voltage is Q = CV, where Q is charge in coulombs, C is capacitance in farads, and V is voltage in volts.

In AC electrical circuits, capacitors are used for three main purposes: motor starting and running, power factor correction, and signal filtering.

For single-phase AC induction motors, a start capacitor is wired in series with the auxiliary (start) winding to create a phase displacement between the main and auxiliary winding currents. This phase displacement produces a rotating magnetic field and starting torque. The start capacitor is disconnected by a centrifugal switch once the motor reaches approximately 75–80 % of full speed — it is rated for intermittent duty only (typically 3–5 seconds per start). A run capacitor remains connected permanently in parallel with the auxiliary winding throughout operation, maintaining a phase shift that improves running efficiency and power factor. Run capacitors are rated for continuous duty with lower capacitance than start capacitors.

For power factor correction, capacitors are installed in parallel with inductive loads (motors, fluorescent light ballasts, transformers) to supply reactive current locally, reducing the reactive current drawn from the supply. This reduces line losses and can reduce electricity tariff charges for industrial consumers billed on kVA demand. Power factor correction capacitors are rated in kilovars (kVAr) rather than farads.

In DC and mixed circuits, capacitors are used as coupling capacitors (blocking DC while passing AC signals), bypass capacitors (filtering supply rail noise), and timing elements in RC circuits.

Polarity matters for electrolytic capacitors — the positive terminal must connect to the more positive point in the circuit. Film capacitors (used for motor applications and AC circuits) are non-polarised and may be connected in either orientation.

Capacitors are used in motor circuits either to provide starting torque (start capacitor) or to improve running efficiency (run capacitor), and many motors use both. A motor wiring diagram with capacitor shows how the capacitor connects in series with the start winding via a centrifugal switch, or permanently across the run winding. GE motor capacitor wiring diagrams, for example, follow the same principle but label terminals T1, T5, and C (common) according to NEMA conventions. Draw or reference any capacitor motor circuit free online with the browser-based wiring diagram maker.

How to wire capacitor wiring diagram

Identify the capacitor type and application Determine whether the capacitor is for motor starting, motor running, power factor correction, or an electronic circuit. Motor capacitors are AC-rated film or electrolytic types with voltage and capacitance markings on the case. Electronic capacitors may be electrolytic (polarised) or ceramic/film (non-polarised). Confirm the type before proceeding — using a polarised capacitor in an AC circuit will cause immediate failure.
Read and record the capacitor's specifications Note the capacitance (in µF for motor capacitors, in kVAr for power factor correction units), the rated voltage (must be equal to or greater than the applied voltage), and for motor run capacitors, the duty rating (continuous). Start capacitors will be marked with a duty cycle or 'non-continuous' indication. Ensure the replacement matches these specifications.
Isolate and discharge before any work Capacitors store charge even after the power is removed. Isolate the supply. Allow the system to rest for at least two minutes; large capacitors may take longer. For motor run capacitors, discharge through a discharge resistor (typically 10–20 kΩ, 5 W, held across the terminals for at least 5 seconds). Verify zero voltage across the terminals with a calibrated multimeter before touching the terminals. Never short a capacitor directly — the resulting arc and current spike can damage equipment.
Wire a motor run capacitor A motor run capacitor wires in parallel with the motor's auxiliary (start) winding terminals. One terminal connects to the auxiliary winding terminal and the other connects to the main supply line (or neutral, depending on motor wiring — refer to the motor wiring diagram). The capacitor is not polarised. Ensure connection terminals are clean and tight.
Wire a motor start capacitor The start capacitor connects in series with the centrifugal switch and the auxiliary winding. Current path: supply line → centrifugal switch → start capacitor → auxiliary winding → neutral. The centrifugal switch removes the capacitor from the circuit automatically once running speed is reached. This series connection is built into the motor's internal wiring on most designs — external access is typically via the motor terminal box.
Wire a power factor correction capacitor (parallel) Power factor correction capacitors connect in parallel with the load they are correcting (across the supply terminals of the motor, lighting panel, or distribution board). Connect across Line and Neutral (single-phase) or Line-to-Line (three-phase) as appropriate. Include a discharge resistor across each capacitor to dissipate charge when de-energised. Fuse the capacitor bank separately.
Restore power and verify operation For motor capacitors, restart the motor and listen for normal operation — a motor with a failed start capacitor will hum without rotating; one with a failed run capacitor will run noisily or draw higher than normal current. Measure motor current and compare to nameplate FLA. For power factor correction, measure power factor before and after with a power analyser or clamp meter with power factor function.

Specifications

Motor start capacitor range	70–300 µF typical, 125–330 V AC rated
Motor run capacitor range	3–70 µF typical, 250–450 V AC rated
Power factor correction unit (kVAr)	Application-specific; sized to bring PF to 0.95 or target value
Start capacitor duty	Intermittent: typically 3–5 s per start, limited starts per hour
Run capacitor duty	Continuous, 24/7 rated
Operating temperature range (run capacitor)	-25 °C to +70 °C or +85 °C depending on class
Self-healing property	Metallised film run capacitors are self-healing at small dielectric breakdown sites
Discharge time (via 20 kΩ resistor)	< 1 minute for capacitors up to 100 µF at 250 V

Safety warnings

Capacitors remain charged after power is removed. Always isolate the supply and discharge the capacitor through a discharge resistor before touching any terminal. Large capacitors can retain enough charge to cause a lethal shock for extended periods — always verify zero voltage with a calibrated voltmeter.
Motor run and start capacitors connected to 230 V AC mains circuits present a shock hazard. All fixed electrical installations must comply with applicable codes (NEC/NFPA 70, BS 7671, AS/NZS 3000, or IEC 60364) and be carried out by a licensed electrician.
Never short a capacitor directly to discharge it. The resulting high-current arc and mechanical shock to the capacitor can rupture the case, damage equipment, and cause injury. Always discharge through a resistor.
A physically damaged capacitor — bulging ends, cracked casing, or signs of electrolyte leakage — must be replaced immediately. A failed capacitor can rupture explosively if re-energised.
Reversed polarity on an electrolytic capacitor will cause rapid failure and possible violent rupture. Double-check polarity before applying power in any DC or mixed-signal circuit.

Tools needed

Digital multimeter with capacitance measurement function
Discharge resistor (10–20 kΩ, 5 W, with insulated leads)
Insulated screwdrivers
Clamp-on ammeter (motor current verification after replacement)
Wire strippers and crimp tool

Common mistakes

Using a DC electrolytic capacitor in an AC motor circuit — AC electrolytic motor capacitors are a specific non-polarised type; using a standard polarised electrolytic in an AC circuit causes immediate failure.
Selecting a replacement capacitor based only on capacitance, ignoring voltage rating — using a capacitor with a voltage rating below the actual circuit voltage will cause premature failure or rupture.
Not discharging the capacitor before working, resulting in a shock from stored energy even after the power is isolated.
Increasing the run capacitor value beyond specification to 'boost performance' — an oversized run capacitor raises current draw in the auxiliary winding, causes overheating, and shortens motor life.
Connecting power factor correction capacitors without discharge resistors — the capacitor retains full charge after de-energising, creating a hazard during subsequent reconnection or maintenance.
Failing to identify and replace a faulty centrifugal switch when replacing a start capacitor on a motor that was burning out start capacitors repeatedly — the root cause is often a stuck centrifugal switch keeping the start capacitor in circuit permanently.

Troubleshooting

Single-phase motor hums but will not start: Cause: Failed start capacitor or stuck centrifugal switch Fix: Isolate and discharge the capacitor. Measure capacitance — if open or well below rated value, replace. If capacitor is good, check the centrifugal switch: it should be closed (continuity) at rest and open when the rotor is at operating speed. A stuck-open switch prevents the start circuit from operating.
Motor runs but draws excessive current and overheats: Cause: Failed run capacitor (open circuit or low capacitance) or wrong capacitor value Fix: Measure capacitance with the capacitor disconnected and discharged. An open circuit or value more than 10 % below rating indicates failure. Replace with the correctly rated capacitor. If the value is wrong (previous incorrect replacement), source the correct value from the motor nameplate or manufacturer's specification.
Capacitor repeatedly fails in the same installation: Cause: Voltage spikes exceeding capacitor rating, or start capacitor left in circuit due to stuck centrifugal switch Fix: Check the circuit voltage against the capacitor's voltage rating — supply voltage fluctuations above rating cause premature failure. For start capacitors that fail repeatedly, inspect the centrifugal switch for sticking. If the switch does not open at operating speed, the start capacitor remains in circuit continuously and fails thermally within minutes.

Frequently asked questions

What is the difference between a motor start capacitor and a run capacitor?

A start capacitor has high capacitance (typically 70–300 µF) and is rated for intermittent duty — it is in-circuit for only 1–5 seconds per motor start before the centrifugal switch disconnects it. A run capacitor has lower capacitance (typically 5–70 µF), is rated for continuous AC duty, and remains permanently in circuit to improve motor running efficiency and power factor.

Why do electrolytic capacitors have polarity and what happens if reversed?

Electrolytic capacitors use an oxide layer as the dielectric, formed during manufacture in one polarity direction. Reversing the polarity breaks down the oxide layer, allowing current to flow and generating heat and gas internally. The result is rapid failure — typically venting of the electrolyte or violent rupture of the capacitor casing. Always connect the positive (marked with a long lead or + symbol) terminal to the more positive point in the circuit.

How do I determine if a motor capacitor has failed?

A failed start or run capacitor is a common cause of single-phase motor failure to start. After isolating and discharging the capacitor, measure capacitance with a capacitance meter. If the reading is more than 10 % below the rated value on the label, or reads open circuit or short circuit, replace the capacitor. A physically bulging, cracked, or leaking capacitor has failed and must be replaced regardless of measurement.

Can I replace a capacitor with a higher capacitance value?

For motor start capacitors, using a significantly higher capacitance than specified increases starting current and can cause the motor to become stuck on the start winding or cause centrifugal switch issues — always match the rated microfarad value within ±5–10 %. For run capacitors, a wrong value alters motor performance, efficiency, and current draw. Voltage rating must equal or exceed the original; capacitance should match the specification.

What does it mean when a capacitor has a kVAr rating?

Power factor correction capacitors are rated in kilovolt-amperes reactive (kVAr) because their purpose is to supply reactive power to offset the reactive power drawn by inductive loads. The kVAr rating describes how much reactive power the capacitor supplies at its rated voltage and frequency. Sizing a correction bank requires calculating the load's reactive power demand and selecting capacitors to bring the power factor to the target value (typically 0.95 or above).

How do I read a motor wiring diagram with capacitor?

In a motor wiring diagram with a start capacitor, the capacitor connects between the start terminal and the supply line through a centrifugal switch that opens once the motor reaches about 75% of rated speed. A run capacitor, by contrast, stays permanently in series with the auxiliary winding while the motor runs. The diagram shows the main winding (usually T1–T4), the auxiliary winding (T5–T8), the capacitor(s), and the centrifugal switch. Always note the capacitor's microfarad rating and voltage rating from the motor's nameplate.

How is a GE motor capacitor wiring diagram laid out?

GE single-phase motors use NEMA-standard terminal labelling: T1 and T4 for the main winding ends, T5 and T8 for the auxiliary winding ends, with a centrifugal switch on the T5 side. The start capacitor connects between T5 (through the switch) and the L1 supply line. For a capacitor-start, capacitor-run motor, an additional run capacitor bridges across the auxiliary winding permanently. Consult the nameplate or the wiring diagram pasted inside the motor conduit box for the exact terminal arrangement specific to your GE frame size and horsepower.