The maximum number of operations the main contacts can perform before their replacement is necessary, in practise is not affected by the class of intermittant duty, but substantially depends upon the value of the current that the contacts have to break and consequently it is strictly in relation with the utilization category and the percentage of inching operations. With reference to the maximum operational current Iem of the contactors (see table n°4), it is possible to determine the averange endurance of contacts as shown in the table N°5.
For the contactors type N1600 to N3000 the duration concerns only the arcing contacts as on these units the main contacts are separated and not involved in the breaking of the current. Therefore, in this case the endurance of the main contacts is pratically unlimited. As already mentioned the endurance shown in the table is related to the maximum operational current Iem ; if the contactor is used at lower ratings, the coefficient K must apply.

Electrical endurance in milion-operation when Ie = Iem
(Table n.5)