International Electrotechnical Commission (IEC) is a European-based
organization that publishes and promotes worldwide mechanical and
electrical standards for motors, among other things. In simple terms,
it can be said that IEC is the international counterpart to the
National Electrical Manufacturers Association (NEMA), which publishes
the motor standards most commonly used throughout North America.
IEC standards are expressed in metric units.
IEC Enclosure Protection Indexes
NEMA, IEC has designations indicating the protection provided
by a motor's enclosure. However, where NEMA designation are in
words, such as Open Drip Proof or Totally Enclosed Fan Cooled,
IEC uses a two-digit Index of protection (IP) designations. The
first digit indicates how well protected the motor is against
the entry of solid objects, the second digit refers to water entry.
way of general comparison, an IP22 motor relates to Open Drip
Proof, IP54 to totally enclosed.
Against Solid Objects
has additional designations indicating how a motor is cooled (two-digit
IC codes). For most practical purposes, IC 01 relates to a NEMA
open design, IC 40 Totally Enclosed Non-Ventilated (TENV), IC 41
to Totally Enclosed Fan Cooled (TEFC), and IC 48 to Totally Enclosed
winding insulation classes parallel those of NEMA and in all but
very rare cases use the same letter designations.
cycles are, however, different. Where NEMA commonly designates either
continuous, intermittent, or special duty (typically expressed in
minutes), IEC uses eight duty cycle designations.
- Continuous duty. The motor works at a constant load for enough
time to reach temperature equilibrium.
S2 - Short-time duty. The motor works at a constant load,
but not long enough to reach temperature equilibrium, and the rest
periods are long enough for the motor to reach ambient temperature.
S3 - Intermittent periodic duty. Sequential, identical run
and rest cycles with constant load. Temperature equilibrium is never
reached. Starting current has little effect on temperature rise.
S4 - Intermittent periodic duty with starting.Sequential,
identical start, run and rest cycles with constant load. Temperature
equilibrium is not reached, but starting current affects temperature
S5 - Intermittent periodic duty with electric braking.Sequential,
identical cycles of starting, running at constant load and running
with no load. No rest periods.
S6 - Continuous operation with intermittent load. Sequential,
identical cycles of running with constant load and running with
no load. No rest periods.
S7 - Continuous operation with electric braking. Sequential
identical cycles of starting, running at constant load and electric
braking. No rest periods.
S8 - Continuous operation with periodic changes in load and speed.
Sequential, identical duty cycles run at constant load and given
speed, then run at other constant loads and speeds. No rest periods.
IEC Design Types
electrical performance characteristics of IEC Design N motors in
general mirror those of NEMA Design B - the most common type of
motor for industrial applications. By the same token, the characteristics
of IEC Design H are nearly identical to those of NEMA Design C.
There is no specific IEC equivalent to NEMA Design D.