What Size VFD for a 5HP Leeson Motor? The Answer Isn't Just the HP Rating

For a standard 5HP, 3-phase AC induction motor, you need a VFD rated for at least 5HP, with an output current equal to or greater than the motor's full-load amps (FLA). At 460V, that's about 7.5–8A. But before you buy, read the nameplate. If your "5HP motor" is a Leeson direct current permanent magnet motor or a brushless motor, a VFD is the wrong tool entirely.

In my role coordinating motor replacements and drive retrofits for manufacturing and material handling clients, I've handled more than 200 rush orders over the last four years, including same-day turnarounds for plants with a line down. Last year alone we processed 47 rush orders for motor drives, and 12 of them were for the wrong type of drive before we implemented our nameplate-check rule. That's a worse failure rate than I'd like to admit, and it's the reason I'm writing this.

Start With the Nameplate, Not the HP Number

I ask every client who calls about a VFD the same thing: send me a photo of the motor nameplate. It sounds almost too simple, but the same "5HP" rating can sit on three completely different motors, and each one needs a different kind of drive:

• AC induction motor – The standard Leeson AC motor. Works with a VFD.
• Permanent magnet DC motor (PMDC) – Needs a DC drive, not a VFD. Leeson makes these in the 1/8 to 2 HP range, running on 90V or 180V DC.
• Brushless DC motor – Needs a matching brushless controller with commutation logic. Neither a VFD nor a conventional DC drive will run it properly.

A VFD outputs a pulse-width-modulated AC waveform. A PMDC motor and a brushless motor don't know what to do with that. The motor may hum, vibrate, overheat, or simply sit there. The expensive mistake happens when a drive fails, someone calls a supplier and says "I need a speed controller for a 5HP motor," and the supplier ships a VFD because 9 out of 10 requests are for AC motors. On installation day, no one is happy.

The Numbers That Actually Matter for Sizing a VFD

For an AC induction motor, sizing comes down to full-load amps rather than the HP label. NEC Table 430.250 lists a 5HP, 3-phase motor at 7.6A for 460V and 15.2A for 230V. The VFD you pick should be rated for at least those current values. That's the part everyone gets right.

Here's the part most guides skip. VFDs are marked with an HP rating that assumes a standard variable-torque load. That's fine for fans and centrifugal pumps. But for constant-torque loads—positive displacement pumps, mixers, conveyors starting under load—I size up one step. A 7.5HP VFD running a 5HP motor is a common, conservative practice. The extra cost is usually around a hundred bucks, and it buys you higher starting torque and fewer nuisance fault trips.

I used to think oversizing was a waste. Then I ran two identical 5HP conveyors side by side, one on a 5HP VFD and one on a 7.5HP. The 5HP drive faulted on startup about 15% of the time in cold weather. The 7.5HP drive never did. Both looked fine on paper—same FLA, same voltage, same load. But the extra headroom was the difference between a line that ran and a line that randomly stopped. Seeing that comparison changed how I recommend drives to anyone running hard loads.

When "5HP Motor" Means a Leeson Direct Current Permanent Magnet Motor

This is where the "what size VFD for 5hp motor" question leads people down the wrong path entirely. Leeson's permanent magnet DC motors are a different species. They need a DC drive that outputs the correct voltage for the motor—typically 90V or 180V depending on the model. If you connect a VFD to a PMDC motor, you won't get speed control. You'll get a motor that doesn't move, or worse, one that heats up until the windings give out.

In March 2024, a client called about a conveyor that had been down for two days. Their DC drive had died, and the maintenance team bought a VFD after describing the motor only as "5HP." When I asked for a nameplate photo, it turned out to be a Leeson 1.5HP permanent magnet DC motor with a 90V armature. The VFD was never going to work. The right DC drive arrived overnight, and the line was back up the next morning. That was a preventable day and a half of downtime. Oh, and the restocking fee on the VFD made it worse.

Mechanical Disc Brakes: The Wiring Detail That Bites

Leeson gearmotors used in lifting and positioning applications often come with mechanical disc brakes. That brake is a separate electrical circuit from the motor, and it has its own wiring considerations when you add a VFD.

If the motor was previously running across the line, the brake coil was probably wired in parallel with the motor. That setup doesn't carry over to a VFD installation. The drive's PWM output waveform can cause the brake coil to chatter, buzz, or burn out. The reliable way to handle it is to power the brake from a separate supply—usually 24V DC—and switch it through the VFD's relay output. Configure the relay so the brake drops in when the drive issues a start command.

For vertical loads, the mechanical brake is your only real holding device in an emergency. A VFD's zero-speed holding torque disappears the moment power is lost. A mechanical disc brake doesn't care about power—it springs to the locked position by default. That's not a detail to get wrong, and it's one of the first things I check when someone orders a motor with a brake for a VFD application.

Brushless Motors: A Third Playbook Entirely

Brushless motors are showing up more often in positioning and servo-type applications. They're efficient, quiet, and precise. But you drive them with a matching brushless controller, not a VFD. The controller handles commutation and needs feedback from Hall sensors or an encoder. The motor is only as good as its controller, and the controller has to match the motor's voltage and current rating.

So if you've got a brushless motor in hand and you're shopping for a way to control it, I'd steer you away from VFDs altogether. Find the motor manufacturer's recommended drive line, or match a controller to the motor's exact specs. It's more of a matched-pair situation than a mix-and-match one.

Where the Simple Answer Stops Applying

There are a few situations where the "pick a 5HP VFD" rule gets complicated:

• Single-phase motors – A 5HP single-phase motor is a different animal entirely. You can't use a standard three-phase VFD on it.
• Extended low-speed running – Below about 30% of base speed, the motor's built-in fan may not deliver enough cooling. At that point, add auxiliary cooling for the motor.
• Outside North America – On 380V or 400V supplies, the FLA values differ. Always size from the nameplate, not from a table written for another voltage.
• Special-purpose motors – Washdown, explosion-proof, or inverter-rated motors have their own requirements. The VFD should match those, not just the horsepower.

For pricing context, based on published listings from January 2025: a 5HP, 460V VFD runs roughly $250–400 for budget models, $450–700 for mid-range units with a NEMA 4X enclosure, and $800–1,500 for premium closed-loop vector drives. A Leeson 5HP AC motor typically lands between $400 and $700 depending on enclosure and efficiency rating. The drive is often the cheaper component—which makes it more frustrating when it's the wrong one.

What This Means for Your Bottom Line

The short answer: for a 5HP AC induction motor, use a VFD rated 5HP (or one size larger for constant-torque loads), and confirm the output current exceeds the nameplate FLA.

The practical answer is bigger than the sizing formula. Verify the motor type before you order anything. A Leeson DC motor needs a DC drive. A brushless motor needs a brushless controller. A VFD is for AC induction motors. If you keep a photo of the motor nameplate in your maintenance folder, you'll cut through most of this confusion in under a minute.

That kind of process discipline isn't bureaucracy—it's efficiency. The five minutes it takes to photograph a nameplate can save you a day of downtime and the cost of two express shipments. I still kick myself for the one time I trusted someone's word on an "AC motor" and skipped the photo request. It was a permanent magnet DC motor, and we lost a full day to the wrong drive. That mistake turned into our policy: no nameplate photo, no expediting.