MANUAL MOTOR STARTER GUIDE
APRIL 19 18/80
2.2.5 Selectivity categories
The IEC 60947-2 defines two different selectivity categories of low-voltage circuit-breakers:
- Category A = Circuit-breakers not specifically intended for selectivity under short-circuit conditions, which
typically do not have any intentional short‐time delay. The short‐time withstand current is not taken into ac-
count.
- Category B = Circuit-breakers specifically intended for selectivity under short-circuit conditions. ABB manual
motor starters are all selectivity category A. Such breakers must have the possibility for a short‐time delay
and also specify a minimum value short‐time withstand current rating according to standard.
2.2.6 Ambient air temperature compensation
Ambient air temperature compensation is realized by utilizing a bimetal which counteracts the working bimetals of
the inverse time-delay thermal over-current release. This second bimetal is not heated by the motor current but
bends only under the influence of the ambient air temperature. As a result, the influence of the ambient air tempera-
ture on the tripping characteristics of the manual motor starter is automatically compensated for, at an ambient
temperature of 20°C.
Figure 5: Diagram for the Ambient air temperature compensation.
The ambient air temperature compensation is defined in IEC / EN 609471-4-1 within a temperature range from –5 to
+40 °C. The ABB manual motor starters have a temperature compensation from -25°C up to +60°C.
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