Electric Motor Control Basics - Book - Page 83
NEMA vs IEC Motor Controls
The International Electrotechnical Commission (IEC) has specified the operational
and performance characteristics for IEC devices in the publication IEC 60947.
Standard sizes are not specified by the IEC. The typical duty cycle of IEC devices are
defined by utilization categories. As far as general motor starting applications are
concerned, AC3 and AC4 are the most common utilization categories.
IEC Category Description
Non-inductive or slightly induction rows
Starting of slip-ring motors
Starting of squirrel-cage motors and switching off only when the motor is up to speed. (Make
LRA, Break FLA)
Starting of squirrel-cage motors with inching and plugging duty. Rapid Start/Stop. (Make and
Auxiliary (control) circuits
Unlike NEMA sizes, they are typically rated by their maximum operating current,
thermal current, HP and/or kW rating.
There are other parameters that are important to consider, while selecting motor
starters, such as time-limit acceleration, current-line acceleration, control voltage,
number of poles, and operating temperature.
Part 1, Contactors
Basics: Part 2,
Basics: Part 3,
The Benefits of Type E/F
Basic Pump Control:
Three Phase DOL Starter
Control of an Electric Pump
Applying Motor Control
in a Wastewater
NEMA vs IEC Motor