A capacitor marked 5/45 can look confusing if you are used to seeing a single capacitance value such as 10 µF or 100 µF. The notation is especially common on dual-run motor capacitors, where one physical component contains two separate capacitance sections.

The important detail is that 5/45 does not mean 5.45 µF, 5–45 µF, or a capacitor with a single variable capacitance. In the typical dual-run configuration, it means 5 µF + 45 µF. Both capacitance sections share a common terminal, while each section serves a different part of the motor system. Commercial examples are commonly specified as 5 & 45 µF, with ratings such as 440 VAC and 50/60 Hz.

That simple marking opens up a useful electronics question: why put two capacitors into one package in the first place?

The answer comes down to motor starting and running requirements, wiring convenience, packaging, and electrical characteristics. Understanding those details also makes it much easier to identify a replacement without accidentally installing the wrong component.

What Does “5/45 Capacitor” Actually Mean?

A 5/45 capacitor normally refers to a dual-value capacitor containing two capacitance values:

• 5 µF for one circuit
• 45 µF for another circuit

The two sections are electrically separate except for their shared common connection.

A typical dual-run motor capacitor therefore has three terminals:

Terminal	Function
C	Common connection
FAN	Fan-side capacitor connection
HERM	Compressor/hermetic-motor connection

The exact terminal labels can vary depending on the application and manufacturer, but the basic concept remains the same.

One capacitor section might provide 5 µF to a fan motor, while the second provides 45 µF to a compressor motor. Instead of installing two individual capacitors, the system can use one compact dual capacitor.

That is why you may see markings such as:

5/45 µF, 440 VAC

or

45/5 µF, 440 VAC

The order itself is not necessarily the important part. The actual terminal labels and capacitance values are what determine which circuit receives which value. A 5/45 µF dual capacitor is also commercially listed as a 5+45 µF device.

Why Are Two Capacitance Values Needed?

A single motor system can contain more than one motor, and those motors may require different capacitor values.

For example, an air-conditioning condenser can contain:

• A compressor motor 
• A condenser fan motor 

These motors do not necessarily have the same capacitor requirements.

The compressor may require a substantially larger capacitance value, while the fan may require a smaller value. A 5/45 capacitor provides both in one enclosure.

This is fundamentally different from putting two capacitors in parallel on a PCB.

For ideal capacitors connected in parallel:

C_total=C₁+C₂

So two 5 µF and 45 µF capacitors connected in parallel would behave as approximately 50 µF between the same two nodes.

A dual-run capacitor is different because its 5 µF and 45 µF sections are independently accessible. They are not simply one 50 µF capacitor.

That distinction matters when troubleshooting or replacing one.

How Does a Dual-Run Capacitor Work?

The basic electrical job of the capacitor is related to the phase relationship between voltage and current in an AC motor.

In a single-phase induction motor, a capacitor can create the phase shift needed to establish a rotating magnetic field and help the motor develop torque.

The capacitor's reactance is:

X_C=1/(2πfC)

where:

• X_C = capacitive reactance in ohms
• f = AC frequency in hertz
• C = capacitance in farads

As capacitance increases, capacitive reactance decreases.

For the same frequency, a 45 µF capacitor therefore has considerably lower capacitive reactance than a 5 µF capacitor.

At 60 Hz, for example, the approximate reactance values are:

Capacitance	Approx. capacitive reactance at 60 Hz
5 µF	531 Ω
45 µF	59 Ω

That difference helps explain why the two capacitor sections can serve very different motor circuits.

However, capacitance alone does not tell you whether a capacitor is suitable. Voltage rating, frequency, temperature, tolerance, physical construction, and application requirements also matter.

5/45 Capacitor vs. 45/5 Capacitor

This is one of the most common points of confusion.

You might encounter:

• 5/45 µF
• 45/5 µF
• 5+45 µF
• 45+5 µF

In many dual-run capacitor applications, these descriptions refer to the same two capacitance values.

For example, a manufacturer may list a product as 5+45 µF, while a supplier lists it as 5/45 µF. The product specifications still identify the two individual capacitance sections.

What you should not do is assume that the position of the number in the product name tells you which physical terminal is which.

Instead, check the capacitor's terminal markings.

For example:

C → common

FAN → 5 µF section

HERM → 45 µF section

The exact arrangement should always be verified against the capacitor label and the equipment wiring diagram.

What Does 440 VAC Mean?

A 5/45 capacitor may also be marked 440 VAC.

That is its rated AC working voltage—not an indication that the capacitor has 440 µF.

This distinction is worth emphasizing because capacitance and voltage are completely different parameters.

For example:

5/45 µF 440 VAC

means:

• First capacitor section: 5 µF
• Second capacitor section: 45 µF
• Rated AC voltage: 440 V

It does not mean:

• 5/45 V
• 445 µF
• 440 µF

A replacement capacitor must have a suitable voltage rating for the application. The correct capacitance values are equally important.

A higher voltage rating can sometimes be acceptable when the physical and electrical requirements are compatible, but the replacement decision should follow the equipment manufacturer's specifications rather than relying on a simple “higher is always better” assumption.

What Happens If the 5 µF or 45 µF Section Fails?

A dual capacitor does not necessarily fail as one perfectly symmetrical component.

One section can degrade while the other remains within specification—or both sections can drift outside their rated tolerance.

A failing capacitor can produce symptoms such as:

• Difficulty starting a motor
• Motor humming
• Reduced motor performance
• Increased operating temperature
• Intermittent operation
• Circuit protection triggering
• A motor that starts only under unusual conditions

However, these symptoms are not unique to capacitor failure. A defective motor, wiring problem, mechanical load, relay, contactor, or power-supply issue can produce similar behavior.

That is why replacing a capacitor based only on a symptom can be a poor troubleshooting strategy.

If the capacitor is suspected, its capacitance should be measured using an appropriate meter and compared with the manufacturer's specified tolerance.

Why Capacitance Tolerance Matters

Suppose a capacitor is rated:

45 µF ±5>#/span###

Its nominal value is 45 µF, but the acceptable range is approximately:

45×0.95=42.75 μF

to

45×1.05=47.25 μF

Similarly, a 5 µF section with ±5% tolerance would theoretically fall between:

4.75 μF

and

5.25 μF

The actual tolerance must be taken from the capacitor's markings or datasheet.

This is particularly important when diagnosing an older capacitor. A component can look physically normal and still have electrically degraded characteristics.

Is a 5/45 Capacitor Used on a PCB?

Usually, no—not in the same sense as the capacitors you normally see mounted on a PCB.

The 5/45 µF dual-run capacitor is primarily associated with AC motor applications, including equipment such as air-conditioning and other motor-driven systems.

PCB capacitors perform a much broader range of functions, including:

• DC decoupling
• Power-supply filtering
• Energy storage
• Signal coupling
• Noise suppression
• Timing
• Voltage stabilization

A PCB designer might use a 5 µF capacitor, a 45 µF capacitor, or completely different values, but the component selection process is based on the circuit's electrical requirements rather than the “5/45” dual-run format.

For PCB manufacturing and assembly, component parameters such as capacitance, voltage rating, dielectric type, package, ESR, ripple current, temperature rating, and availability can all affect the design. These are the kinds of component and manufacturing details that need to be considered when taking a PCB from design into production, something PCBMASTER also addresses through PCB and PCBA manufacturing support.

Can You Replace a 5/45 Capacitor With Two Separate Capacitors?

Electrically, it may be possible to reproduce the two capacitor functions with two individual capacitors, but that does not automatically make it a suitable replacement in every piece of equipment.

The original dual capacitor may have been selected for:

• Electrical specifications
• Physical dimensions
• Terminal arrangement
• Environmental conditions
• Mounting method
• Vibration resistance
• Safety requirements
• Motor-specific characteristics

Replacing one dual capacitor with two individual components can therefore create mechanical and wiring issues even if the nominal capacitance values look correct.

For equipment repair, the safest starting point is generally the manufacturer's specified replacement part or an electrically and mechanically compatible equivalent.

How to Choose a Replacement 5/45 Capacitor

When you are looking for a replacement, don't search only for “5/45 capacitor.”

Check the complete specification.

1. Verify both capacitance values

You need the correct combination:

5 µF + 45 µF

Do not substitute a 5 µF + 40 µF or 5 µF + 50 µF capacitor simply because it physically fits.

2. Check the voltage rating

If the original is rated at 440 VAC, verify the replacement against the equipment requirements.

3. Check the frequency

Many motor-run capacitors are specified for 50/60 Hz, but the application should determine the required rating.

4. Check tolerance

Capacitance tolerance can affect motor operation, so compare the replacement's tolerance with the original specification.

5. Check the terminals

A capacitor with the correct capacitance but incompatible terminal configuration can still be the wrong part.

6. Check the physical dimensions

Diameter, height, mounting arrangement, terminal position, and enclosure style can all matter.

7. Check the application

A motor-run capacitor should not automatically be replaced with any capacitor that happens to have the same capacitance and voltage rating.

The capacitor's construction and intended duty cycle matter as well.

5/45 Capacitor vs. Ordinary PCB Capacitor

The difference becomes clearer when you compare their typical roles.

Characteristic	5/45 Dual-Run Capacitor	Typical PCB Capacitor
Typical capacitance format	Two values in one component	Usually one value
Typical application	AC motor circuits	Electronic circuits
Common connection	Shared common + two outputs	Two terminals
Typical voltage	High AC voltage	Application dependent
Main purpose	Motor phase-shift/run operation	Filtering, coupling, storage, decoupling
Physical format	Can-style motor capacitor	Radial, SMD, film, ceramic, etc.
Selection priorities	Motor requirements + AC rating	Circuit requirements + electrical characteristics

This is also a good reminder that the word “capacitor” describes a component family, not one standardized component type.

A 100 nF MLCC on a high-speed PCB and a 45 µF motor-run capacitor may both store electrical energy, but their construction, application, electrical behavior, and selection criteria can be dramatically different.

Practical Troubleshooting: Don't Judge a Capacitor by Appearance

One of the traps with older motor capacitors is assuming that physical appearance tells you everything.

A capacitor may be:

• Bulged
• Leaking
• Discolored
• Damaged around the terminals

Those are useful warning signs, but the absence of visible damage does not prove that the capacitor is healthy.

Electrical measurement is more informative.

If you are working on mains-connected motor equipment, remember that capacitors can retain dangerous electrical energy after power has been removed. Appropriate isolation, discharge procedures, test equipment, and electrical safety practices are essential.

For hobbyists and makers, this is one area where “just swap the part and see what happens” is a particularly bad debugging strategy.

Why the 5/45 Marking Is Still Useful

Once you understand the notation, 5/45 is actually a compact piece of information.

It immediately tells you that the component contains two capacitor sections with different capacitance values. Combined with the voltage and frequency markings, the label provides a quick starting point for identifying the component.

The bigger lesson is useful beyond motor capacitors: component markings are shorthand, not complete specifications.

A number printed on a component may identify capacitance, resistance, voltage, tolerance, temperature characteristics, polarity, package information, or even a manufacturer's internal code. Before replacing an unfamiliar component, it is worth identifying what each part of the marking actually represents.

FAQ: 5/45 Capacitor

What is a 5/45 capacitor?

A 5/45 capacitor is typically a dual-run capacitor containing 5 µF and 45 µF capacitor sections in one physical package.

Is a 5/45 capacitor the same as a 45/5 capacitor?

In many product listings, yes. Both describe a dual capacitor with 5 µF and 45 µF sections. Always verify the terminal labels and equipment wiring rather than relying only on the order of the numbers.

What does 5/45 µF 440 VAC mean?

It means the capacitor has 5 µF and 45 µF sections and a 440 VAC voltage rating.

Can I replace a 5/45 capacitor with a 50 µF capacitor?

Not as a direct equivalent in a dual-run application. A single 50 µF capacitor does not provide the same independently accessible 5 µF and 45 µF sections.

What is the 5 µF section normally used for?

In common dual-run motor applications, the smaller section may be used for a fan motor, while the larger section may serve a compressor or another motor circuit. The actual application should be confirmed from the equipment documentation.

Can a 5/45 capacitor be used on a PCB?

A dual-run 5/45 µF motor capacitor is generally not a substitute for the capacitors used in PCB power, signal, or filtering circuits. PCB capacitor selection depends on the electrical and physical requirements of the specific circuit.

Final Takeaway

A 5/45 capacitor is usually a dual-value motor-run capacitor: 5 µF + 45 µF in one package. Its purpose is not to create a single 50 µF capacitance, but to provide two separately usable capacitor sections for different parts of a motor system.

When identifying or replacing one, look beyond the “5/45” marking. Check the capacitance values, voltage rating, frequency, tolerance, terminal configuration, physical dimensions, and application requirements.

That same habit—reading the complete electrical specification instead of focusing on one number—is valuable throughout electronics. Whether you are troubleshooting a motor circuit or selecting components for a PCB, the right component is determined by how its complete specification matches the circuit, not simply by whether one number looks familiar.

For PCB projects, that becomes even more important as designs move from prototype to production. Component selection, PCB fabrication, assembly, and testing all have to remain aligned with the electrical requirements of the finished product. A manufacturing partner such as PCBMASTER can support that broader PCB/PCBA workflow when a design moves beyond individual component selection and into production.