Where would you absolutely need both standards? Any application combining VFDs, long cables, and wide speed variation.
Before diving into the specifics of Part 32 and 33, it is essential to understand the parent document. is the definitive standard for motors and generators in North America. It covers everything from frame sizes and dimensions to performance characteristics, efficiency, and safety.
An AMP-33 motor rated for 10 HP at 60 Hz can provide 10 HP from 33 Hz to 60 Hz (constant torque). Below 33 Hz, if you want 10 HP (i.e., high torque at low speed), you must either: nema mg1-32 amp- 33
: Standardized testing procedures in Part 32 evaluate breakdown torque , locked-rotor current, and efficiency under variable load conditions.
Specifically, NEMA MG1 Part 33 outlines requirements for motors used in specialized, high-demand applications. While "AMP-33" is not a standard industry term like "NEMA Code Where would you absolutely need both standards
MG1-32 assigns a series of "Code Letters" (A through V) to motors to indicate the range of locked-rotor kVA per horsepower. This allows engineers to size circuit breakers, fuses, and starters appropriately without needing to test every single motor.
For a motor to be labeled (often called "Inverter Duty" or "VFD Rated"), it must withstand: is the definitive standard for motors and generators
Therefore, are not legacy standards—they are living requirements for reliability. For any engineer specifying a motor for a new VFD system, ignoring these sections is gambling with premature failure. A motor that truly meets both MG1-32’s electrical endurance and AMP-33’s thermal realism will deliver years of service in the harshest industrial environments.
Within MG-1, specifically address the operation of AC motors powered by solid-state variable frequency drives (VFDs) . As VFDs became ubiquitous in the 1990s, motor failures spiked due to issues like voltage spikes, bearing currents, and poor cooling at low speeds. NEMA responded by creating these sections to define "Inverter Duty" motors versus standard sine-wave motors.
According to MG1-33, an compliant motor must be capable of the following: