What Is an Electrical Reactor? Line Reactors vs. Load Reactors

An electrical reactor is an inductive component that uses a coil to resist changes in current. In a variable frequency drive (VFD) system, a line reactor is installed on the incoming power side of the drive, while a load reactor is installed between the drive and the motor. Both add inductance, but they address different electrical conditions, so they are not interchangeable by default.

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We help B2B buyers compare reactors by looking first at where the component will be installed and what problem it needs to address. Line reactors are generally considered for input-side current disturbances and drive protection; load reactors are generally considered for output-side effects associated with the VFD-to-motor connection. Correct selection depends on the drive, motor, supply, cable, and operating conditions.

What Does an Electrical Reactor Do?

A reactor is an inductor, typically built from a winding around a magnetic core. Its inductance opposes rapid changes in current, helping limit current transients and shaping the electrical conditions seen by connected equipment. In power systems, the word “reactor” can also describe devices used for other purposes, but this article focuses on series reactors used with VFDs.

A reactor does not perform the same job as a transformer, circuit breaker, or dedicated harmonic filter. It can influence current and voltage behavior, but the result depends on the reactor’s electrical rating and the system it is connected to. For that reason, a reactor should be selected against the equipment manufacturer’s requirements and the actual installation conditions.

Line Reactors vs. Load Reactors: The Main Difference

The clearest distinction is position in the circuit. A line reactor is connected between the incoming AC supply and the VFD input; a load reactor is connected between the VFD output and the motor. Because the two locations expose the reactor to different waveforms and problems, their selection criteria also differ.

How a Line Reactor Works

A line reactor adds impedance between the supply and VFD. Depending on the installation, this can help limit the rate or magnitude of some input-side current changes and reduce the effect of certain supply disturbances on the drive. It may also be specified as part of a drive manufacturer’s recommendations or an engineered power-quality solution.

Line reactors are often described by impedance percentage. 3% and 5% impedance are commonly encountered rating options, but neither value is automatically right for every drive. The appropriate rating must be checked against the drive’s input current, supply conditions, allowable voltage drop, and system design.

How a Load Reactor Works

A load reactor is placed on the VFD output, where it adds inductance to the drive-to-motor circuit. This can moderate output current changes and help address some motor-cable and motor-terminal stresses associated with the VFD’s switched output. Its suitability depends on factors such as cable length, motor insulation, drive characteristics, and the manufacturer’s guidance.

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A load reactor is not the same as a dV/dt filter or a sine-wave filter. Those devices have different designs and output characteristics. If an application has strict motor-terminal voltage-rise limits, long cable runs, or sensitive motor insulation, confirm whether a reactor is sufficient or whether a more specialized output filter is required.

When Should You Consider Each Type?

Consider a Line Reactor When

• The VFD manufacturer recommends input-side impedance for the drive or installation.
• The supply has conditions that warrant engineering review, such as switching events or interaction with other equipment.
• You need to evaluate input-side current behavior as part of a broader drive or power-quality design.

A line reactor is not a universal cure for voltage problems, harmonics, or nuisance trips. First identify the cause of the issue, and check whether the reactor’s impedance and current rating fit the system. If the concern is significant, review the full installation with a qualified electrical engineer or the drive supplier.

Consider a Load Reactor When

• The motor is connected to a VFD and the output circuit needs additional inductance.
• The motor cable arrangement or installation distance raises questions about output waveform effects.
• The drive or motor manufacturer recommends an output reactor for the specific operating conditions.

Do not assume that every VFD-to-motor installation needs a load reactor. A short, standard installation may not require one, while a more demanding cable or motor condition may call for a reactor or a different output device. Use the drive and motor documentation to establish the requirement rather than choosing by name alone.

How to Select an Electrical Reactor

1. Define the problem and location. Decide whether the concern is on the supply side of the VFD or between the VFD and motor.
2. Record the electrical ratings. Gather supply and drive voltage, rated current, phase, and operating frequency. Many industrial systems operate at 50 Hz or 60 Hz, but the reactor must match the application’s actual rating.
3. Confirm the required impedance and duty. For a line reactor, check the specified impedance and allowable voltage drop. For a load reactor, confirm compatibility with the drive output and expected motor duty.
4. Document the installation. Provide motor details, cable type and length, enclosure conditions, ambient temperature, and available mounting space where relevant.
5. Check system compatibility. Verify the reactor’s current and voltage ratings, thermal requirements, connection arrangement, and any drive-specific instructions before ordering.

For example, a buyer evaluating a 480 V, three-phase drive should share that voltage along with the drive’s rated input or output current, depending on reactor location. This is an example of information to provide, not a recommendation that every 480 V system use a particular reactor. The required rating and impedance should be confirmed for the actual equipment and operating conditions.

Common Selection Mistakes

• Choosing by name only: “Reactor” does not identify whether the component is designed for the line or load side.
• Assuming line and load reactors are interchangeable: They operate in different parts of the circuit and must be rated for their intended position.
• Ignoring cable and motor information: Output-side selection may depend on the connection between the VFD and motor.
• Treating a reactor as a complete filter: A reactor may not provide the attenuation or waveform characteristics required for a particular power-quality or motor-protection target.
• Overlooking installation conditions: Current, voltage, frequency, temperature, enclosure, and cooling can affect suitability.

What Buyers Should Provide to a Supplier

To make a technical review more useful, share the single-line diagram or a clear description of where the reactor will be installed. Include the VFD model or electrical ratings, supply voltage, phase, rated current, motor data, and—when considering a load reactor—motor cable details. Also state the issue you want to address, such as an equipment recommendation, an input-side concern, or a motor-cable application.

At ANNEZEE, we support B2B inquiries by reviewing application requirements and matching them with reactor specifications, including electrical ratings and installation constraints. Buyers should confirm the final selection against their drive and motor documentation and applicable project requirements. Providing complete technical information at the inquiry stage helps reduce avoidable specification mismatches.

Key Takeaways and Next Steps

• An electrical reactor is an inductor that opposes rapid changes in current.
• A line reactor goes on the VFD input side and is considered for input-side conditions.
• A load reactor goes between the VFD and motor and is considered for output-side conditions.
• Neither type is a universal solution; ratings and application requirements determine suitability.

In short, choose a line reactor when the requirement concerns the supply-to-drive side, and consider a load reactor when it concerns the drive-to-motor side. Before requesting a quotation, gather the drive and motor ratings, installation position, cable information, and the problem you need to solve. ANNEZEE can use those details to help assess a suitable specification for your electrical equipment project.

For more information, please visit What Is an Electrical Reactor? Line Reactors vs Load Reactors.