Electric Motor Control Basics - Book - Page 44
Industrial Control Basics: Part 3, Starters
IEC Rating
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, the AC3 and AC4 are the most common utilization categories.
IEC Rating
Utilization Category
IEC Category Description
AC1
Non-inductive or slightly induction rows
AC2
Starting of slip-ring motors
AC3
Starting of squirrel-cage motors and switching off only when the motor is up to speed.
(Make LRA, Break FLA)
AC4
Starting of squirrel-cage motors with inching and plugging duty. Rapid Start/Stop. (Make
and Break LRA)
AC11
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 when selecting motor
starters, such as time-limit acceleration, current-line acceleration, control voltage,
number of poles, and operating temperature. These parameters are not covered in
this article.
Industrial Control
Basics:
Part 1, Contactors
Industrial Control
Basics: Part 2,
Overload Relays
Industrial Control
Basics: Part 3,
Starters
The Benefits of Type E/F
Motor Protection
Circuit Breakers
Basic Pump Control:
Three Phase DOL Starter
Control of an Electric Pump
Applying Motor Control
in a Wastewater
Application
NEMA vs IEC Motor
Controls
Understanding
IP Ratings
44
