Product Manual

IEC Cooling, Insulation and Duty Cycle Indexes
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 to Totally Enclosed Non-Ventilated (TENV), IC 41 to
Totally Enclosed Fan Cooled (TEFC), and IC 48 to Totally Enclosed Air
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 equi-
librium 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, electric
braking, and rest. Temperature equilibrium is not reached.
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.
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