This International Standard is applicable to high-voltage switchgear and controlgear (scope of IEC SC 17A) and assemblies thereof (scope of IEC SC 17C) and specifies equipment for digital communication with other parts of the substation and its impact on testing. This equipment for digital communication, replacing metal parallel wiring, can be integrated into the high-voltage switchgear, controlgear, and assemblies thereof, or can be an external equipment in order to provide compliance for existing switchgear and controlgear and assemblies thereof with the standards of the IEC 61850 series.