This Recommendation provides guidance on voltages and currents that may safely be used to power telecommunication systems that are part of the telecommunications service provider's network. These systems use the paired-conductor cables of the network to provide power to communications-related equipment at remote locations. This equipment and the current-carrying conductors can be accessed in the energized state by service or skilled personnel without using insulated gloves or tools. These systems are not intended to extend a voltage-limited remote feeding telecommunication (RFT-V) or a current-limited RFT (RFT-C) circuit beyond the point of demarcation between the service provider and the end user or ordinary people. In addition, exposed RFT-V and RFT-C circuits are not allowed to be accessible to ordinary people or end users. The systems that use RFT-C and RFT-V are located in the network between different telecommunication centres, between a telecommunication centre and a telecommunications access facility or node, and between a telecommunication centre and public network interfaces (PNIs). This Recommendation covers only systems that use continuous direct current (d.c.) powering.

RFT circuits sometimes carry signalling or data on the conductors, as well as delivering power. However, in many cases the conductors are used to simply provide d.c. power and no signalling or data is present. This is becoming more commonplace, as fibre is used more and more to transmit broadband data and twisted pair copper cable pairs are used to power remote telecommunications equipment.

Figure 1-a shows the field of application in the network between different telecommunication centres. Figure 1-b shows the part of the access network where this Recommendation is applicable. If there is no access network equipment between the local exchange and the customer premises equipment to convert the RFT-V or RFT-C to telecommunication network voltage-1 (TNV-1), TNV-2, TNV-3, energy source class 1 (ES1) or energy source class 2 (ES2), this Recommendation does not apply.

Guidance on work practices, if these limits are exceeded, can be found in [b-ITU-T Directives Vol. VI] and [b-ITU-T Directives Vol. VII].

NOTE 1 – Limits on permissible voltages that may occur because of exposure to power or electrified railway lines are provided in [b-ITU-T Directives].

NOTE 2 – Requirements for the safety of equipment that is part of the telecommunications network infrastructure are provided in [b-ITU-T K.51], [IEC 60950-1] and [IEC 62368-1].