States the characteristics of control circuit devices, the electrical and mechanical requirements, the various duties to be performed, the significance of the rated characteristics and of the markings, the tests to verify the rated characteristics, the functional requirements to be satisfied by the control circuit devices, environmental conditions, including those of enclosed equipment, dielectric properties, terminals. This publication supersedes IEC 337-1 (1970) and its Amendment 1 (1983), supplements 337-1A (1973) and 337-1B (1975), 337-2 (1972) and its Amendment 1 (1975), supplements 337-2A (1973), 337-2B (1976) and 337-2C (1977). It should be read in conjunction with IEC 947-1.