An electrical reactor is an inductor used in a power circuit to oppose changes in current. In a variable frequency drive (VFD) system, a line reactor is installed on the drive’s incoming power side, while a load reactor is installed between the drive and the motor. They are both inductive components, but they act at different points in the system and address different application concerns. The right choice depends on whether you need to manage incoming supply disturbances or conditions on the drive-to-motor connection.
An electrical reactor is a coil designed to provide inductance in an electrical circuit. Inductance opposes changes in current, so a reactor can affect the magnitude and rate of current changes depending on its design and where it is installed. Reactors are commonly used in AC power systems, including VFD installations, to help manage electrical behavior. Their effects depend on factors such as the circuit voltage, current, frequency, reactor impedance, and connected equipment.
In a VFD installation, a reactor may help limit certain current transients and reduce the impact of electrical disturbances on connected equipment. A line reactor can also contribute to reducing harmonic current, although the result depends on the drive, supply, and system configuration. On the output side, a load reactor can moderate some voltage and current transients between the drive and motor. A reactor does not, by itself, guarantee a specific power-quality result or protect against every fault condition.
Reactors are used in industrial and commercial systems where equipment such as VFDs, motors, and power conversion devices must operate within the limits of the installation. A line reactor may be considered when the supply is subject to disturbances or when the drive manufacturer recommends input impedance. A load reactor may be considered when the motor connection requires additional output-side inductance. System conditions and the equipment manufacturer’s instructions should guide the decision.
The main difference is their position in the circuit. A line reactor is installed on the VFD input, where it interacts with the incoming AC supply. A load reactor is installed on the VFD output, where it interacts with the drive’s switched output and the motor circuit.
| Comparison point | Line reactor | Load reactor |
|---|---|---|
| Typical location | Between the AC supply and VFD input | Between VFD output and motor |
| Primary application focus | Supply-side current behavior and drive input conditions | Drive output and motor-cable conditions |
| Potential system value | May limit some current transients and help reduce harmonic current | May moderate output-side transients and help reduce stress on the motor connection |
| Key selection inputs | Supply voltage, frequency, drive input current, and required impedance | Drive output current, motor voltage, cable arrangement, and application requirements |
A line reactor is connected in series with the incoming supply to the drive. Its inductance opposes rapid changes in current and adds impedance to the input circuit. This can help reduce the effects of some supply-side current transients and may reduce harmonic current drawn by a drive, depending on the installation. It is not a complete harmonic filter, and its performance should not be assumed without evaluating the drive and supply conditions.
Some drive applications use a reactor specified at 3% impedance, but that figure is an example of a commonly encountered design value, not a universal requirement. The appropriate impedance and current rating depend on the drive, supply voltage, and the system’s operating requirements. Always check the equipment documentation and confirm the required configuration before ordering.
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A load reactor is installed on the output side of a VFD, in series between the drive and motor. It adds inductance to the output circuit and can moderate some of the voltage and current transients produced by the drive. This may be useful when the motor connection or cable arrangement calls for additional output-side impedance. A load reactor is not automatically equivalent to a dv/dt filter or sine-wave filter, so the selected component must match the actual motor and cable requirements.
VFD output is produced through switching rather than as a simple utility-frequency sine wave. The motor’s fundamental operating frequency can vary with the drive’s commanded speed, while the supply may be rated for 50 Hz or 60 Hz. The output-side component must be selected for the drive and motor circuit, not just by matching the supply frequency shown on the site nameplate.
Confirm the system voltage, phase configuration, drive input or output current, and operating frequency before comparing products. The reactor’s current and voltage ratings must be suitable for the circuit where it will be installed. Also verify the required impedance, enclosure, mounting method, ambient conditions, and applicable installation constraints. If any values are uncertain, consult the drive documentation or a qualified electrical professional.
If the concern is on the incoming supply side, evaluate a line reactor and check whether the drive manufacturer specifies one. If the concern is between the drive and motor, evaluate a load reactor or another output-conditioning option according to the cable and motor requirements. Long motor cables, sensitive insulation, or particular drive configurations may call for a dedicated filter rather than a basic reactor. The correct choice cannot be determined from the term “electrical reactor” alone.
Reactor construction and component choices vary by design and application. When comparing products, review the rated voltage and current, impedance, frequency range, temperature rise or thermal limits where specified, insulation system, terminals, enclosure, and mounting details. Request technical documentation that allows your engineering or procurement team to verify the selected model against the installation. A supplier should be able to clarify which ratings are available and what information is needed to assess a match.
At ANNEZEE, we support B2B buyers evaluating electrical equipment and reactor requirements by discussing the application, electrical ratings, and installation constraints. To help us assess a request, provide the drive model or input/output ratings, system voltage and frequency, motor details, and whether the reactor is intended for the input or output side. If cable length or a specific power-quality concern is relevant, include that information as well. Final selection should be confirmed against the equipment manufacturer’s instructions and the project’s electrical design.
An electrical reactor is an inductor used to oppose changes in current, but a line reactor and a load reactor serve different parts of a VFD system. Choose a line reactor when the requirement concerns the incoming supply and drive input; choose a load reactor when it concerns the drive output and motor connection. First identify the electrical issue, then confirm the circuit location and required ratings rather than selecting by product name alone. Share your system details with ANNEZEE to discuss a suitable reactor specification and next steps for your procurement inquiry.
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