Normal and heavy duty ratings are about the overload capability of the VFD, because overloading affects the ability of the transistors to stay cool enough. "Normal Duty", aka "Variable Torque", is for centrifugal pumps and fans, because they physically cannot be overloaded without needing to shut down, so the VFD overload capability is lower. Everything that is not a CENTRIFUGAL pump or fan requires a "Heavy Duty" (a.k.a. Constant Torque) rated drive, which is generally the "next size up" in order to attain that added thermal capacity of the transistors. You did say "pumps", but what KIND of pumps are they? Positive Displacement Pumps like like gear pumps, screw pumps, progressive cavity pumps and and piston pumps are Heavy Duty loads. Turbine, axial and impeller pumps are Normal Duty.
The VFD, depending on age, will have a listed MAXIMUM over current protective device, either fuses or a circuit breaker of some type, and pay attention to the details, because if they do not give a circuit breaker size, then you CANNOT assume they are listed to be used with a circuit breaker, it might be fuses ONLY. It happens a lot more than you might think. You can go smaller than maximum on the OCPD size, but the smaller you get, the easier it is to get nuisance tripping. If the VFD is one designed and listed after 2020, it must now meet a new UL standard that dictates a MINIMUM size as well. So again, read the details.
The major mfr. that uses Normal and Heavy Duty instead of VT & CT for the ratings, is Rockwell. All of the Rockwell drives in this size are listed with breakers, but the newer PowerFlex 755T Series are listed under the new rules that have a minimum size rating of 125% of the MOTOR FLA for circuit breakers. But if you use the PowerFlex 753, which is older, you have no minimum size.
Amazing! Now that I would love to see a pic of.