This technical report applies to equipment interfaces. These interfaces within the equipment may be connected to telecommunication networks, may form part of the telecommunication network infrastructure or may provide localized transfer of data. This technical report provides guidance on the classification of interfaces in accordance with the circuit types defined in IEC 60950-1 and IEC 60950-21 following an analysis of the telecommunication network characteristics. This technical report only covers equipment appropriately interconnected. Furthermore, it does not address damage caused by one equipment to another equipment to which it is connected. Exceptionally, interfaces may be designed for higher or lower levels for special applications. In such cases it should be ensured that only interfaces having the same safety category and protection level are connected together. This is based on the available specifications of the equipment manufacturers and network providers, and on information regarding the installation category of the mains interface. This technical report is intended to be used by equipment designers, network operators, network regulators/authorities, standards writers and network installers. It is applicable to various interfaces of equipment. Network presentations are not equipment and so are not covered by IEC 60950-1 and IEC 60950-21; hence they are also not covered by this technical report. However, it is necessary to consider the characteristics, installation and presentation of telecommunication networks when determining what equipment interface requirements apply (for example, SELV circuit, TNV-1 circuit, TNV-2 circuit, TNV-3 circuit etc.). If a standard other than IEC 60950-1 or IEC 60950-21 is used for designing the equipment and its interface (for example, IEC 62151 in conjunction with other product safety standards), then the corresponding requirements of these other standards are to be preferred. If there is a conflict between this technical report and a more detailed specification, the latter prevails. This technical report applies regardless of ownership or responsibility for installation and maintenance of the equipment or network. NOTE Terminal equipment is often connected to customer premises cabling when used in a business environment, and there are standards covering such cabling.