What Size VFD for 5HP Motor? A TECO Electric Buying Guide for Cost-Conscious Teams

A question I get far too often in purchasing is simple: what size VFD for a 5HP motor? The short answer is usually a 5HP VFD, but that answer only works after you look at the motor nameplate, the connected load, and the available input voltage. I manage the motor and drive budget for a 180-person automation company, and I have tracked every VFD order for more than six years. This checklist is what I open whenever a 5HP quote lands on my desk.

Before we get to the steps, one cost disclaimer: the cheapest quote at the bottom of the page is not necessarily the cheapest drive on the panel. A low-priced drive can become the most expensive part of your project after a service visit, a replacement unit, and a missed customer deadline. I will show you where those hidden costs hide.

Here is the checklist I use. It has six steps, and step 4 is the one most first-time buyers fail to ask about.

Step 1. Start With Motor Full-Load Amps, Not the Horsepower

The motor nameplate is the only valid starting point. A 5HP motor can have different full-load amps depending on enclosure, insulation class, design type, and efficiency. According to NEC Table 430.250 (NFPA 70, 2023), a typical 5HP three-phase motor draws about 15.2A at 230V and 7.6A at 460V. But the actual motor on your machine may show 13.8A or 16.4A. The nameplate wins.

Look for the VFD output current rating. It should be equal to or higher than the motor full-load amps. If the product label says 5HP normal duty and 3HP heavy duty, do not rely on the horsepower name. Use the rated output current in the manual.

This is also the step where I have a strong opinion: choose by current, but do not automatically add one frame size. Oversizing changes the cost and can make the protection less precise. Undersizing by one amp causes nuisance trips and hidden downtime. Real talk: oversizing by one frame can add 20 to 30 percent to the quote. Undersizing by one amp can stop a line during startup and look like a drive failure, so a technician swaps the VFD before anyone checks the motor. That is how a simple replacement becomes a repair story.

Step 2. Match the VFD Rating to the Load Torque Profile

Now close the motor catalog and write down what the motor is driving. A centrifugal pump or fan is a variable-torque load. A conveyor, extruder, or positive displacement pump is usually constant torque. A loaded mixer or punch press may require high starting torque for a few seconds. The same 5HP VFD can handle one of these perfectly and fail on another through no fault of the motor.

For example, if a conveyor has a heavy belt and starts with product on it, the VFD needs to produce enough current for the breakaway torque. That means I look for a heavy-duty current rating, not just the normal-duty horsepower number. In my own records, a 5HP conveyor with a higher service-factor motor needed a drive rated one frame larger because the normal-duty output current was too low.

There is a lot of automation news about motion control, and I read it to avoid missing a better machine concept. Still, a servo motor news article does not answer this choice. A servo motor is the right tool when the load accelerates fast and must hold a position with high stiffness. Stepper motors make economic sense for lower-speed indexing and simpler point-to-point moves. But for a 5HP fan, pump, conveyor, or machine spindle running continuously, a conventional TECO Electric AC motor is still the right foundation, and a VFD is the throttle on it.

Step 3. Check the Input Voltage and Phase Before You Pick a Frame

The VFD must be rated for the input line voltage. If the motor is connected for 460V but your plant supply is 480V, make sure the drive input accepts 480V. If the motor is wired for 230V, the full-load current is roughly twice the 460V value, so the VFD output current rating needs to be checked against the same voltage.

Single-phase supply is a common surprise. Many small VFDs accept single-phase input and output three phases, but at 5HP the frame may not be listed for that input. If the manual does not say single-phase input is allowed, get a different drive. Do not assume a 5HP drive can be fed from a standard outlet just because it is small enough to pick up.

Step 4. Overload Rating and Duty Cycle Are the Real Crossroad

Here is the forgotten step. Two VFDs can both say 5HP on the box and not have the same current rating. The difference is the overload profile. A drive marked 5HP normal duty may provide 150 percent current for 60 seconds. The next model may provide 150 percent for only 30 seconds, or 110 percent in a high ambient temperature. The manual will state overload capability for each duty class.

For applications where the motor starts under load or repeatedly accelerates before reaching full speed, select a drive with a heavy-duty current rating. That may be a larger frame than a standard 5HP pump drive. It is not a mistake; it is the correct product.

I can give you a concrete example. In Q2 2024, I compared three quotes for a 5HP conveyor drive at our plant. The first quote was $212 lower than the second. The supplier said the normal-duty rating was plenty. I sent the purchase order anyway, and I immediately wanted to take it back. What if the belt was heavier than the drawing? It was. The drive tripped during the first loaded start, and the manufacturer blamed the application. The replacement quote was for the second drive I had not ordered. Looking back, the extra $212 was trivial compared to two service calls and a late machine. Now my quote matrix has a separate line for overload class.

Step 5. Download the Current Manual and List Every Required Accessory

This step sounds administrative, but it prevents the biggest balloon payment on a project. When the quotation arrives, ask for the current manual. If your distributor offers customer portal access, request a TECO Electric login for their documentation and order history. Do not depend on a PDF that came from a previous project. Manufacturers change default parameters, terminal functions, and output ratings without a public announcement.

Supplier portals also vary in the way they spell the brand. Some list TECO-Electric with a hyphen while another page says TECO Electric and Machinery. Check the model number and datasheet revision, because the logo can cause more confusion than it solves.

Then list the accessories: input fuses, line reactor, EMC/RFI filter, remote keypad, braking resistor, enclosure, and panel cooling. Most VFD manuals have a derating curve for high ambient temperature and high switching frequency. If your cabinet has no cooling and the drive runs at a high carrier frequency, the output current capability is lower than the printed spec. That hidden derating is exactly where a cheap quote falls apart.

What is inside the panel also talks before you do. Your customer’s electrician sees cheap components and starts doubting the machine builder. The drive quality forms part of your brand impression. I would rather spend an extra few hundred dollars on a drive with proper documentation and support than explain to a customer why their line did not start.

Step 6. Compare Total Landed Cost, Not the Line Price

At this point you know the required size and the duty cycle. Now create a comparison table across suppliers. Include drive price, shipping, taxes, duties, panel integration time, programming, accessories, spare part strategy, and the probable cost of one unplanned outage. The initial line price is only the first row.

In a mid-2024 quote review, I compared three legitimate 5HP-rated VFD suppliers. The lowest quote was about 27 percent below the highest one. After adding a line reactor, an enclosure kit, and a communication adapter, the low quote was only 5 percent below the high quote. The high quote included two hours of application support and a faster warranty response. I chose the higher quote and felt relieved rather than annoyed. The machine started without a field trip.

So what size VFD for a 5HP motor? The paper answer is: choose a VFD whose output current rating matches or exceeds the motor full-load amps, with a duty rating that covers the driven load. For most 5HP motors on 460V, that is a 5HP-rated drive with enough heavy-duty current headroom. For hot cabinets and special loads, use the manufacturer derating curves.

If you are asking this question for a quote, use this checklist so you can compare TECO Electric and other suppliers on exactly the same specification. Bottom line: the lowest price is not real until every term is identical, and the best drive is the one that does not call attention to itself.