This part of EN 60947 applies to a.c. semiconductor non-motor load controllers and contactors intended for performing electrical opertions by changing the state of a.c. electric circuits between the ON-state and the OFF-state. As controllers, they may be used to reduce the amplitude of the r.m.s. a.c. voltage on the load terminals from that of the applied voltage - either continuously or for a specified period of time. The half-wave period of the a.c. wave form remains unchanged from that of the applied voltage. They may include a series mechanicall switching device and are intended to be connected to circuits, the rated voltage of which does not exceed 1000 V a.c. The semiconductor controllers and contactors dealt with in this standard are not normally intended to interrupt short-circuit currents. Therefore, suitable short-circuit protection should form part of the installation but not necessarily of the controller itself. In this context, this standard gives requirements for semiconductor controllers and contactors associated with separate short-circuit protective devices.