Within the IEC 61439 series of standards for low-voltage switchgear and controlgear assemblies, there are system and application details that are specified by the specifier to enable the manufacturer to produce an assembly that meets the needs and expectations of the specifier.

This part of IEC 61439, which is a technical report, identifies from the specifier's perspective those functions and characteristics that are defined when specifying assemblies. It provides:
- an explanation of the assembly characteristics and options within the IEC 61439 series;
- a guidance on how to select the appropriate options and define characteristics so as to meet specific application needs; and
- an assistance in the specification of assemblies.

References within this document to the interface characteristics of an assembly and the requirements with which they will comply assume that the assembly is designed, manufactured, and verified in accordance with the relevant part of the IEC 61439 series.