Applies to contactors intended for closing and opening electric circuits, and, if combined with suitable relays, for protecting those circuits against operating overloads which may occur therein. Intended to state the characteristics of contactors; the conditions with which contactors shall comply with reference to their operation and behaviour and their dielectric properties; the tests intended for confirming that these conditions have been met and the methods to be adopted for these tests; the data to be marked on the apparatus.