IEC 60364-4-43:1977

Sets out general rules for protection of live conductors against overload and short circuit.
Specifies the features of various protective devices and necessary coordination between conductors and overload protective devices. Formula for calculation of time in which a given short-circuit current will raise a conductor from the highest admissible temperature in normal duty to its limit temperature. Enumerates requirements for coordination of overload and short-circuit protection.

Note: For details of
-low-voltage circuit breakers, see IEC 60947-2
-low-voltage fuses, see IEC 60269
-for coordination of low-voltage direct-online (full voltage) motor starters with short-circuit protective devices, see IEC 60947-1
-for current-carrying capacities of conductors for electrical installations of buildings, see IEC 60364-5-523.