The RS OC/x output chokes can be used in conjunction with the filters to improve EMC performance. They are especially effective where radiated emissions from long drive to motor cables are a problem e.g. corruption of near by control or data cable signals or radio / television interference. The correct fitting of an RS OC/x into the motor cable can eliminate these problems.
The details of each product give approximate motor kW ratings for the RS OC/x chokes but the selection is ultimately governed by the type and thickness of motor cable fitted i.e. the motor cable must fit through the OC centre hole.