The 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.
Dimensionally, IEC standards are expressed in metric units.
IEC Enclosure Protection Indexes
Like 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.
By way of general comparison, an IP22 motor relates to Open Drip Proof,
IP54 to totally enclosed.
Protection Against Solid Objects
#
Definition
0
No protection.
1
Protected against solid objects of
over 50mm (e.g. accidental hand contact).
2
Protected against solid objects of
over 12mm (e.g. finger).
3
Protected against solid objects of
over 2.5mm (e.g. tools, wire).
4
Protected against solid objects of
over 1mm (e.g. thin wire).
5
Protected against dust.
6
Totally protected against dust.
Does not involve rotating machines.
Protection Against Liquids
#
Definition
0
No protection.
1
Protected against water vertically dripping
(condensation).
2
Protected against water dripping
up to 15º from the vertical.
3
Protected against rain falling at up to 60º
from the vertical.
4
Protected against water splashes from all
directions.
5
Protected against jets of water from all
directions.
6
Protected against jets of water comparable
to heavy seas.
7
Protected against the effects of immersion
to depths of between 0.15 and 1.0 m.
8
Protected against the effects of prolonged
immersion at depth.
IEC Cooling
IEC 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 Over
(TEAO).
IEC winding insulation classes parallel those of NEMA and in all but
very rare cases use the same letter designations.
Duty cycles are, however, different. Where NEMA commonly designates
either continuous, intermittent, or special duty (typically expressed in
minutes), IEC uses eight duty cycle designations.
S1 - 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 rise. 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
The 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.
