|
 INTRODUCTION
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
|
Number
|
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. |
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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.
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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.
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