Page 505 - Motor protection and control Manual motor starters, contactors and overload relays

ABB MOTOR PROTECTION AND CONTROL 3/431

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Temporary or intermittent duty

Utilization of contactors for temporary / intermittent duty 03
The table below shows the factor (known as "On-load factor") to be applied to the rated operational current Ie / AC-1 to obtain the
permissible operational current Ie / AC-1 in relation to the switching frequency and the current flow time per cycle.
Operating cycles per hour 1 2 3 6 12 20 30 60 120
Prefered classes acc. to IEC 60947-4-1 1 – 3 – 12 – 30 – 120
Current flow time per cycle Factors applicable to Ie / AC-1
5 s 5.2 5 4.9 4.7 4.3 4.0 3.7 3.4 2.8
10 s 3.8 3.7 3.6 3.4 3.1 3.0 2.8 2.6 2.2
20 s 2.8 2.7 2.7 2.6 2.5 2.4 2.2 2.0 1.5
30 s 2.4 2.3 2.3 2.2 2.1 2.1 1.9 1.7 –
40 s 2.2 2.1 2.1 2.0 1.9 1.9 1.7 1.5 –
60 s 1.9 1.8 1.8 1.8 1.7 1.7 1.5 – –
Example:
AF09 contactor (intermittent duty, resistive load)
Rated operational current Ie / AC-1 at 60 °C
(see "Technical data: main pole utilization characteristics") 25 A
Switching frequency 2 operating cycles/h
Current flow time per cycle 20 s
Factor to be applied to the current Ie / AC-1 2.7
Permissible current: 2.7 x 25 = 67 A

1SBC101971S0201