This part of IEC 60947 applies to a.c. semiconductor non-motor load controllers and contactors intended for performing electrical operations by changing the state of a.c. electric circuits between the ON-state and the OFF-state. Typical applications are given in table 2.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 mechanical switching device and are intended to be connected to circuits, the rated voltage of which does not exceed 1 000 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 (see 8.2.5) 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.This standard does not apply to- continuous operation of a.c. motors;- low-voltage a.c. semiconductor motor controllers and starters covered by IEC 60947-4-2; - electronic a.c. power controllers covered by IEC 60146; - all-or-nothing solid-state relays.Contactors and control-circuit devices used in semiconductor controllers and contactors should comply with the requirements of their relevant product standard. Where mechanical switching devices are used, they should meet the requirements of their own IEC product standard and the additional requirements of this standard.The object of this standard is to statea) the characteristics of semiconductor controllers and contactors and associated equipment;b) the conditions with which semiconductor controllers and contactors should comply with reference to- their operation and behaviour;- their dielectric properties;- the degrees of protection provided by their enclosures, where applicable;- their construction;c) the tests intended for confirming that these conditions have been met, and the methods to be adopted for these tests;d) the information to be given with the equipment or in the manufacturer's literature.