VFD Selection: Check Current, Overload and Operating Duty

Before using a VFD sizing tool, describe the job the drive must perform. Two motors with the same power rating can serve machines with very different duty cycles.

One may run at a steady load. The other may accelerate frequently, hold torque at low speed or experience short load peaks. A power label alone does not explain that difference.

The useful starting question is: what must the motor and drive do throughout the operating cycle?

Describe the cycle before choosing the drive

Record the required speed range, load changes, acceleration periods and frequency of starts. Separate normal running from short-duration peaks.

Motor current, load profile, acceleration requirements and operating duty should be considered together before selecting a drive.

You can also review the motor application through the Ruhify W60 Industrial Electric Motor page to keep the motor-side requirements connected to the drive selection process.

Read the complete rating

An overload percentage needs a duration and a repetition interval to mean anything useful. Likewise, a continuous current rating must be checked against the actual operating conditions.

A drive that appears suitable from motor kW alone may still be inadequate if the application requires repeated acceleration, high starting torque, low-speed operation or short-duration overloads.

Ask the supplier to show where the proposed drive meets your documented duty. Keep that confirmation with the selected model and rating table.

Build a short selection brief

Use five sections:

motor nameplate data

operating cycle

site conditions

control requirements

unresolved questions

Attach a readable nameplate photograph and identify whether each load value comes from measurement, calculation or an assumption.

If the process changes between products or shifts, include those cases explicitly.

For example, describe:

“Six starts per hour with the attached acceleration profile.”

rather than:

“Frequent starting.”

The first statement gives the reviewer something concrete to check.

Keep the decision traceable

When the supplier revises the selection, record what changed and why.

A different rating may reflect an updated load case rather than an arbitrary increase in drive size.

This becomes especially important when several engineers, suppliers or project teams review the same motor-drive combination.

Prepare your Ruhify sizing case

Ruhify includes a VFD / ASD Sizing & Selection Suite for building a more structured preliminary drive-sizing case.

Start with:

Motor data → Operating cycle → Current → Overload requirement → Site conditions → Preliminary selection

The goal is not simply to match a drive kW rating to a motor kW rating.

The goal is to understand whether the proposed drive can support the actual operating duty.

You can use the Ruhify AI Agent to interact with product and engineering knowledge, while Ruhify AI Search can help users find relevant product information, tools and technical content without manually navigating through pages.

Explore the broader platform at Ruhify.

A preliminary calculation is most useful when it exposes the assumptions behind the selection and identifies the next question that needs to be answered.

This is a preliminary selection workflow. Final drive and motor coordination requires validated manufacturer data and qualified engineering review.