A pump drive keeps tripping after a new machine starts elsewhere in the building. Someone suggests adding a reactor. It sounds like a quick fix, but pump VFD input reactor decisions should begin with the incoming power, not with a guess about accessories. A reactor may reduce certain electrical stresses. It will not repair a loose connection, an undersized cable, a failing generator, or a pump that is overloading its motor.
The short answer: do not add one to every installation by default. Check the drive manual, the supply conditions, and the fault pattern first. Then ask the drive supplier and a qualified electrical designer whether input impedance is needed for this particular drive and site.
What an input reactor actually sits between
An input reactor is installed on the supply side of the VFD. It adds impedance between the source and the drive. That can help when the incoming supply is unusually stiff or electrically noisy, and it can reduce some current peaks and harmonic effects. It is not the same as an output filter placed between the drive and the motor. Mixing up the two is especially risky when the real concern is a long motor cable.
Schneider Electric’s line-reactor guidance makes a useful point: even within one drive family, the answer depends on voltage, power quality, and whether a DC choke is already part of the design. That advice is specific to Schneider equipment, not an installation rule for BEDFORD drives. The general lesson is to read the exact model’s input requirements before buying an accessory.
Three questions before you buy a pump VFD input reactor
- When does the problem occur? Record the fault code, time, operating speed, and what else switched on or off. If faults appear when a large load starts, measure the supply at the drive terminals during that event. If faults appear during deceleration, look at the stopping ramp and the pump’s operating conditions too; an input reactor alone may not address a rising DC bus.
- What is feeding the drive? Note the transformer or generator rating, source voltage, phase balance, cable run, protective devices, and other drives on the same feeder. A generator needs its own review: voltage regulation and harmonics can change the decision.
- What does the drive already contain? Some models incorporate a DC choke or other input measures; others do not. Confirm the exact model, voltage class, current, and approved reactor range with its manufacturer. Adding impedance also creates a voltage drop, so a weak supply deserves careful checking rather than automatic addition.
These checks are more useful than a blanket percentage rule. They tell you whether the proposed part addresses the observed symptom.
Where a reactor will not help
If the pump trips only when a valve closes or when the motor accelerates, investigate hydraulic loading, acceleration settings, motor current, and control signals first. If a cable joint heats up, fix the joint. If insulation is stressed by a long drive-to-motor cable, review output-side protection; an input reactor does a different job. And if someone proposes using a three-phase drive on single-phase power, stop and confirm that the exact drive is approved for that supply. Schneider’s single-phase guidance explicitly warns that not every drive is suitable.
For an industrial pump panel, the BEDFORD B503PRO product page is a starting point for a model review, not evidence that every B503PRO needs an input reactor. Confirm the exact voltage class, motor current, site fault level, supply quality, and any approved input accessories before finalizing the panel. If you are still matching the drive to the motor, our pump inverter sizing guide explains why kW alone is not enough.
The useful request to send your supplier
Send a photo of the drive and motor nameplates, the single-line diagram, measured line voltage under load, the fault history, and the proposed reactor specification. Ask one specific question: Which measured condition would this reactor correct on this exact model? If the answer cannot be tied to a condition, keep diagnosing before ordering parts.