What Is an Electrical Reactor? Line Reactors vs. Load Reactors
An electrical reactor is an inductive component that uses a coil to oppose changes in current. In industrial systems, reactors are commonly installed with variable frequency drives (VFDs) to help manage current disturbances and protect connected equipment. A line reactor is installed on the input side of a drive, while a load reactor is installed on its output side, between the drive and motor. The right choice depends on where the electrical issue occurs and what equipment needs protection.
You can find more information on our web, so please take a look.
At ANNEZEE, we help buyers evaluate reactor requirements by looking at system voltage, operating current, frequency, installation position, and the drive and motor configuration. These details matter because a reactor is not a universal fix for every power-quality or motor-cable issue. The guide below explains how reactors work and how to distinguish line-side from load-side applications.
Key Takeaways
- A reactor is an inductor that limits the rate of change in current and contributes impedance to a circuit.
- A line reactor is connected before the VFD; a load reactor is connected after the VFD.
- Line reactors are considered for input-side disturbances and drive protection, while load reactors address certain output-side conditions.
- Selection should be based on the equipment manufacturer’s requirements and the actual electrical installation, not on reactor type alone.
What Is an Electrical Reactor?
An electrical reactor is a coil, typically wound around a magnetic core, designed to provide inductance in an AC circuit. Inductance creates opposition to changes in current, and the resulting impedance depends on factors including inductance and operating frequency. For an ideal inductor, reactance is calculated as XL = 2πfL, where f is frequency and L is inductance.
For example, an ideal 1 mH inductor has a reactance of approximately 0.377 Ω at 60 Hz. This is a calculated illustration, not a specification for a particular reactor; actual equipment performance also depends on its design, current, core, and operating conditions. In practical installations, engineers select reactors by matching electrical ratings and application requirements rather than relying on inductance alone.
Core Functions in a Drive System
In a VFD system, a reactor adds impedance that can help reduce the severity of current changes and electrical disturbances. Depending on its position and design, it may help limit certain transient currents, reduce stress on connected equipment, or improve compatibility with the installation. Its exact effect varies with the drive, supply, motor, cable, and system conditions.
A reactor does not replace correct grounding, suitable cables, protective devices, or the drive manufacturer’s installation guidance. It also cannot be assumed to eliminate harmonics, voltage events, or motor insulation stress in every application. For complex systems, the reactor should be selected as part of an overall electrical design.
Line Reactors vs. Load Reactors
The principal difference is location. A line reactor is installed between the electrical supply and the VFD input, whereas a load reactor is connected between the VFD output and the motor. Because they operate on different sides of the drive, they address different parts of the system and are not automatically interchangeable.
| Comparison point | Line reactor | Load reactor |
|---|---|---|
| Typical position | Supply side, before the VFD | Motor side, after the VFD |
| Primary application focus | Input-side conditions and drive input protection | Output-side conditions between the VFD and motor |
| Common evaluation factors | Supply voltage, phase, drive input current, and system conditions | Drive output current, motor voltage, cable arrangement, and drive requirements |
| Key limitation | Does not directly condition the VFD-to-motor output | Does not address disturbances arriving at the VFD input |
When a Line Reactor May Be Appropriate
A line reactor may be evaluated when the supply has disturbances or when the drive installation calls for additional impedance at its input. It can also be considered in systems where drive input current changes or interaction with other equipment is a concern. The required solution depends on the specific supply and drive, so the equipment documentation and an electrical assessment should guide the decision.
Line reactors are used on single-phase and three-phase systems, subject to the reactor’s ratings and the application design. Many industrial systems operate at 50 Hz or 60 Hz, but the selected reactor must match the actual system frequency and voltage. Buyers should also verify that its current rating is suitable for the drive input and operating conditions.
When a Load Reactor May Be Appropriate
A load reactor may be considered where a VFD drives a motor through output wiring that presents concerns identified by the drive or motor manufacturer. It can add impedance on the drive output and may be specified to help manage certain output-side effects. Whether it is suitable depends on factors such as motor characteristics, cable arrangement, switching conditions, and the drive’s recommendations.
ANNEZEE supply professional and honest service.
A load reactor is not the same as a sine-wave filter or a dv/dt filter. Those devices have different designs and performance objectives, and a reactor alone may not meet the requirements of a particular motor or cable installation. If the project has long motor leads or specific insulation constraints, consult the drive and motor documentation before choosing an output device.
How to Choose the Right Reactor
1. Identify the Side of the Drive
First determine whether the issue is on the supply side or between the drive and motor. If the concern relates to the incoming power, evaluate a line-side solution. If it relates to the drive output or motor circuit, assess a load-side option and compare it with any filter requirements.
2. Confirm Electrical Ratings
Provide the system voltage, phase, frequency, and the relevant drive input or output current. The reactor must be specified for the correct position and electrical duty; a current value taken from the wrong side of the drive can lead to an unsuitable selection. As an example of a common specification convention, some applications use a reactor with 3% impedance, but this is not a universal requirement or a substitute for checking the drive manufacturer’s guidance.
3. Review Installation Conditions
Consider enclosure space, ambient conditions, ventilation, cable routing, and how the reactor will be mounted and connected. Reactors can generate heat during operation, so the installation must allow for the manufacturer’s clearance and thermal requirements. Confirm terminal arrangements and protection coordination before ordering.
4. Request a Specification Review
Before procurement, share the drive model, motor data, supply details, intended installation position, and any known cable or power-quality concerns with the supplier. This information helps identify missing requirements and reduces the risk of comparing products with different ratings. For projects with unusual conditions, request engineering review rather than selecting solely by nominal current.
Common Selection Mistakes
- Choosing by name alone: “Line reactor” and “load reactor” describe position and application, not a complete specification.
- Confusing a reactor with a filter: A reactor does not necessarily provide the same output waveform or mitigation as a dedicated filter.
- Ignoring drive guidance: Drive manufacturers may define when an input or output reactor is required and what ratings are acceptable.
- Overlooking heat and space: Electrical ratings must be considered alongside installation and thermal conditions.
Supplier Support and Sourcing Considerations
For B2B procurement, a useful supplier should be able to clarify the product’s electrical ratings, connection position, dimensional information, and available configuration options. Ask for a datasheet and confirm that voltage, current, frequency, impedance, and terminals correspond to the project specification. If the application is not fully defined, provide the available system information so the supplier can identify questions that need resolution before quotation.
At ANNEZEE, we support reactor inquiries by reviewing application details and helping buyers align product specifications with their equipment and sourcing requirements. Availability, customization, minimum order quantities, and lead times can vary by model and order scope, so we recommend confirming these points during quotation. For repeat or OEM procurement, sharing drawings, labeling needs, and packaging requirements early can make product evaluation more straightforward.
Conclusion: Which Reactor Do You Need?
An electrical reactor is an inductive component that adds impedance to help manage current behavior in an electrical system. A line reactor is installed before the VFD and is evaluated for input-side conditions; a load reactor is installed after the VFD and is considered for output-side conditions between the drive and motor. The correct choice depends on where the concern occurs, the drive and motor requirements, and the reactor’s electrical ratings.
As a next step, collect the drive model, supply voltage and frequency, relevant current rating, motor data, and cable information. Then confirm the intended reactor position and any impedance or filter requirements against the equipment documentation. Contact ANNEZEE with these details to discuss a suitable specification and request a quotation for your project.