Line Reactors vs DC Chokes vs Input Filters – Which One Does Your VFD Need?
Variable Frequency Drives (VFDs) are sensitive to supply quality. Poor incoming power, voltage spikes, and harmonic distortion can cause nuisance trips, overheating, and premature failure.
That’s why many installations use line reactors, DC chokes, or input filters to protect both the drive and the electrical network. But which one do you actually need?
In this guide, we explain the differences between each option, how they work, and when to use them with your inverter drives, motors, and industrial machinery.
Why VFD Input Protection Matters
VFDs draw current in short pulses rather than smooth sine waves. This creates:
- Harmonic distortion
- Voltage spikes
- High inrush currents
- Electrical noise (EMC issues)
Without proper protection, you may experience:
- Overcurrent trips
- Overvoltage faults
- Reduced drive lifespan
- Interference with nearby equipment
Input protection devices smooth and stabilise the supply to improve reliability.
What Is a Line Reactor?
A line reactor (AC reactor) is an inductor installed on the incoming AC supply to the VFD. It limits rapid current changes and smooths the waveform.
What Line Reactors Do
- Reduce current spikes
- Limit inrush current
- Protect against voltage transients
- Reduce harmonics
- Improve drive lifespan
When to Use a Line Reactor
- Weak or unstable supply
- Multiple drives on same feeder
- Long supply cables
- Generator power
- Frequent VFD trips
Line reactors are one of the most common and cost-effective protections for VFD installations.
What Is a DC Choke?
A DC choke is installed inside the VFD’s DC bus rather than on the AC input. Many modern drives include an internal or optional DC choke.
What DC Chokes Do
- Reduce DC ripple current
- Lower harmonic distortion
- Improve power factor
- Reduce stress on capacitors
- Improve efficiency slightly
When to Use a DC Choke
- Where harmonics must be reduced
- Medium-to-large drives
- Installations with many drives
- Where space is limited (internal solution)
DC chokes are often a neat, built-in solution but typically offer less surge protection than a dedicated line reactor.
What Is an Input Filter?
Input filters are designed primarily for EMC (electromagnetic compatibility) and electrical noise suppression.
What Input Filters Do
- Reduce electrical noise
- Meet EMC regulations
- Prevent interference with other equipment
- Improve compliance in commercial buildings
When to Use Input Filters
- Sensitive electronics nearby
- Office or commercial environments
- PLC or communication issues
- EMC compliance requirements
Filters control noise but do not provide the same surge or harmonic protection as reactors.
Line Reactor vs DC Choke vs Input Filter – Quick Comparison
- Line reactor: best for surge protection & current limiting
- DC choke: best for harmonic reduction inside the drive
- Input filter: best for EMC/noise suppression
Each solves a different problem — they are not direct replacements for each other.
Which One Should You Choose?
Choose a Line Reactor if:
- Your drive trips on overcurrent or overvoltage
- Supply is unstable
- Running from generators
- You want maximum protection
Choose a DC Choke if:
- You want harmonic reduction
- The drive supports internal chokes
- Space is limited
Choose an Input Filter if:
- You have EMC interference issues
- Signals/PLCs are affected
- You need regulatory compliance
Can You Use More Than One?
Yes — many industrial installations combine:
- Line reactor + EMC filter
- DC choke + filter
This provides both protection and compliance.
Real-World Example
Application: 15 kW conveyor drive
Problem: Random overcurrent trips and supply noise
Solution:
- Install line reactor for surge protection
- Add EMC filter for noise reduction
Result: Stable operation and fewer faults.
Common Mistakes
- Assuming all filters are the same
- Ignoring supply quality
- Only fixing problems after repeated failures
- Using oversized drives instead of proper protection
Frequently Asked Questions
Do small VFDs need reactors?
Not always, but protection improves reliability and lifespan.
Is a DC choke the same as a line reactor?
No. They are installed in different places and solve different problems.
Will a filter stop overcurrent trips?
No. Reactors reduce current spikes; filters mainly reduce noise.
Are reactors worth the cost?
Yes. They are far cheaper than replacing a failed drive.
Do modern drives include DC chokes?
Many mid-to-large drives include them internally or as options.
Need Help Protecting Your VFD?
At Drive Outlet Megastore, we supply reliable inverter drives, electric motors, geared motors, and accessories to keep your systems running smoothly.
If you’re unsure whether you need a line reactor, DC choke, or filter, contact our team and we’ll help you select the correct solution for your installation.
