The IEC 62386 series specifies a bus system for control by digital signals of electronic lighting equipment. This electronic lighting equipment should be in line with the requirements of IEC 61347, with the addition of d.c. supplies. This part of IEC 62386 is applicable to control gear supporting centrally supplied emergency operation as described in EN 50171. Emergency operation can be triggered in two ways. Either by failure of the normal supply and establishment of emergency supply or by short circuiting the bus. In both cases the control gear will operate at a predefined light level. This part does not apply to self-contained emergency lighting control gear. Those control gear are specified in IEC-62386-202.