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Contactor selection starts from motor full load current, then applies the utilisation category: AC-3 for normal starting, AC-4 for plugging and jogging where the contacts break locked-rotor current and need roughly double the rating. High starting frequency adds a further factor.
Contactor sizing
required rating = motor FLC x category factor x starting frequency factor
AC-3 breaks running current; AC-4 breaks starting current, which is six times higher. AC-4 duty therefore demands a much larger contactor for the same motor.
No. A contactor only switches. Overload protection comes from a thermal overload relay or electronic protection relay in series with it.