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

An electrical reactor is an inductor used in an AC power system to limit or shape current, reduce the effects of electrical disturbances, or help protect connected equipment. In a variable frequency drive (VFD) system, a line reactor is installed on the drive’s incoming power side, while a load reactor—also called an output reactor—is installed between the drive and the motor. The right choice depends on where the electrical problem occurs: upstream of the drive or downstream between the drive and motor.

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These devices are not interchangeable. A line reactor can help reduce the impact of supply-side disturbances and limit current changes into a drive, while a load reactor can help manage the drive’s output waveform and motor-cable effects. At ANNEZEE, we recommend selecting a reactor from the system details—not from the name alone.

Key Takeaways

• A line reactor is installed between the AC supply and the VFD input.
• A load reactor is installed between the VFD output and the motor.
• Both are inductive components, but they address different parts of a drive system.
• Selection should account for voltage, current, frequency, installation conditions, and the drive and motor manufacturers’ requirements.

What Is an Electrical Reactor?

Basic Definition and Operating Principle

An electrical reactor is a coil designed to provide inductance in an AC circuit. Inductance opposes changes in current, so a reactor can help limit current surges and influence how electrical energy flows through a system. Unlike a transformer, a standard reactor is not primarily used to transfer power between separate windings at a changed voltage.

Reactors are used in many power and industrial applications, including drive systems, power-quality equipment, and other circuits that need current limiting or electrical filtering. Their performance depends on their electrical rating and the conditions in which they operate. A reactor should therefore be selected for the specific circuit rather than treated as a universal accessory.

Line Reactor vs. Load Reactor

Where Each Reactor Is Installed

A line reactor is connected on the input side of a VFD, between the AC supply and the drive. It adds impedance to the incoming circuit, which can help limit the rate and magnitude of current changes reaching the drive. Depending on the installation, it may also help reduce the drive’s effect on the supply system.

A load reactor is connected on the output side, between the VFD and the motor. It is used to help manage the electrical output delivered through the motor cable, particularly where the drive’s switching and the cable installation are relevant design considerations. It does not replace correct motor-cable selection or compliance with the drive manufacturer’s installation instructions.

What Does a Line Reactor Do?

Supply-Side Applications

A line reactor can be considered when a drive is exposed to supply-side disturbances, when current changes need to be moderated, or when the application design calls for additional impedance at the drive input. It may also be part of a broader power-quality approach. The specific benefit depends on the source, the drive, and the rest of the electrical system, so it should not be assumed to resolve every voltage or harmonic issue.

Line reactors are often specified by impedance as a percentage of the relevant base voltage and current. 3% impedance is a commonly encountered option, while 5% impedance is also used in some designs; neither value is automatically correct for every drive. Confirm the required value with the drive manufacturer or a qualified electrical designer, especially if the supply has high impedance or the drive’s operating requirements are sensitive to voltage drop.

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What Does a Load Reactor Do?

Drive-to-Motor Applications

A load reactor is used on the VFD output side to add inductance between the drive and motor. In some installations, it can help moderate output current changes and reduce the stress associated with the drive-to-motor connection. Its suitability depends on the drive’s output characteristics, the motor, cable construction, and cable length.

There is no single motor-cable length at which every system needs a load reactor. VFD manufacturers set different limits and may recommend different output components for different drive models and operating conditions. Check the drive documentation before adding an output reactor, and consider whether the application instead requires a dV/dt filter or sine-wave filter.

How to Choose the Right Reactor

Check System Ratings and Installation Details

1. Identify the problem location. If the concern is on the incoming supply or drive input, evaluate a line reactor. If the concern is on the drive output or motor-cable side, evaluate a load reactor or another output solution.
2. Confirm electrical ratings. Provide the system voltage, phase, operating current, and frequency. Many industrial systems operate at 50 Hz or 60 Hz, but the reactor must be rated for the actual application and operating conditions.
3. Review drive and motor guidance. Check the VFD manual for input and output component requirements, motor compatibility, and permitted cable arrangements. Do not assume that a reactor approved for one side of the drive can be moved to the other.
4. Account for the installation environment. Consider enclosure space, mounting, ambient conditions, ventilation, and connection requirements. These factors can affect the reactor specification and installation plan.
5. Confirm the design before ordering. Share the application details with your supplier or electrical designer and verify the selected impedance, current rating, and configuration against the equipment documentation.

Common Selection Mistakes

A frequent mistake is choosing a reactor based only on the motor’s rated power. Power rating alone does not provide all the information needed to match a reactor to a VFD circuit. Buyers should also confirm voltage, current, frequency, impedance requirements, and whether the component will be installed at the input or output.

Another mistake is treating a reactor as a replacement for other power-quality or motor-protection equipment. A line reactor does not guarantee elimination of harmonics or all supply disturbances, and a load reactor is not automatically equivalent to a dV/dt or sine-wave filter. If the application involves long motor leads, sensitive equipment, or specific compliance requirements, consult the drive manufacturer and a qualified engineer.

Supplier Support and Sourcing Considerations

Information to Include in an Inquiry

When requesting a quotation, provide the reactor type, installation position, system voltage, phase, frequency, rated current, and any required impedance. For a load reactor, include the VFD model, motor details, and motor-cable information where available. For a line reactor, share the supply and drive input details, as well as any known application requirements.

At ANNEZEE, we work with B2B buyers to clarify application requirements and identify suitable electrical equipment options. Clear specifications help us assess the request and discuss configuration, documentation, and sourcing requirements. Final compatibility should be confirmed against the equipment manufacturer’s instructions and the project’s electrical design.

Conclusion: Which Reactor Should You Choose?

An electrical reactor is an inductive component used to influence current in an AC circuit. Choose a line reactor when the design calls for impedance on the supply side of the VFD, and consider a load reactor when the requirement concerns the drive-to-motor output circuit. The installation position is the clearest starting point, but it is not the only selection criterion.

Before purchasing, confirm the system ratings, the drive manufacturer’s recommendations, and the actual issue the reactor is intended to address. If you are sourcing for a project, send ANNEZEE the drive and motor details, electrical ratings, and installation requirements so we can review the inquiry and discuss an appropriate reactor solution.

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