Committed to connecting the world

Question 19/5

Question 19/5 – Power feeding systems
(Continuation of Question 19/5)


Along with the widespread use of the Internet, a great deal of ICT equipment, such as routers, servers, and switches, has been installed in telecommunication centres to enable high-speed and large-scale broadband services.

A DC power feeding system is commonly used inside a telecommunication centre because power efficiency is higher than that of an AC power feeding system due to few conversion stages in series, and a direct connection to the batteries. AC and 48V are commonly used in data centres, but higher DC voltage solutions are proposed to unify the power interface with higher efficiency and reliability solution.

The power consumption per rack of conventional (legacy-type) equipment such as exchanges or transmission devices or routers and servers has reached higher amounts of kW. Therefore, the feeding current is over a hundred amperes when a 48Vdc power feeding system is used to supply power to ICT equipment. Moreover, the feeding cable must have sufficient capacity for the current, so the diameter of the cable becomes wider. This situation has several disadvantages such as length limitation, voltage drop caused by cable resistance, heavy weight, and inflexibility. As a result, the higher voltage solution is also proposed for telecommunication centres to obtain a higher level of optimization.

However, power feeding systems in telecommunication centres, for example, are not specified in International standards. Along with the increase in energy consumption of the devices, energy efficiency of the feeding system is also an important factor in reducing the CO2 produced by ICT systems. Moreover, these disadvantages may lead to the use of a great amount of materials, such as copper and plastics, and may require significant consumption of energy to construct those systems.

Therefore, it is important to consider not only the energy consumption of the telecommunication devices, but also the whole life cycle impact including the manufacturing phase and the validity of the energy supply to the equipment.

This work, directly and indirectly, contributes to a reduction in the environmental impact of ICTs, e.g., CO2 and material use.

In addition, the development of renewable energy is on the rise these days. This will increase energy efficiency and reduce the amount of manufactured equipment, thus leading to indirect environmental impacts.

These renewable energy sources are inter alia PV systems, wind generators, Fuel Cells or external engine generators such as Stirling motor using biofuels. For the latter, there is also a possibility to use solar power.

The following Recommendation, in force at the time of approval of this Question, falls under its responsibility:

  • L.1200


This Question mainly focuses on the energy efficiency of the power feeding systems that are used in telecommunication networks or customer premises. To achieve higher energy efficiency, this Question will prepare methodologies for evaluating the energy efficiency of power feeding systems including AC and DC systems, specifications on power feeding systems, safety issues for devices and service personnel, and methods for constructing an earthing and bonding system. One of the key issues is the characterization of a Higher Voltage DC power feeding system, the voltage of which is around 400 V. The Higher Voltage DC power feeding system is a topic of great interest around the world because of its ability to improve the energy efficiency of the power feeding system. The standardization of its specifications is very important to promote the development of the system and improve the validity of the energy supply to the ICT system.

In addition, it is important to have a general study on renewable energy and to understand and coordinate renewable energy systems to the new DC power interface to enable more use of renewable energy.

Study items to be considered include, but are not limited to:

  • Specification of the power feeding systems, especially for the Higher Voltage DC systems;
  • Nominal voltage, operation voltage range, abnormal voltage range under fault condition, etc.;
  • Safety criteria and requirements for service personnel and equipment.
      1) Protection (blocking) devices such as fuses, breakers, etc.
      2) Basic principle for safety and working practices,
      3) Requirements and criteria for protecting service personnel and equipment under normal and abnormal operating conditions;
  • System configuration and specification of the power feeding system
      1) Cable distribution method, basic concept (or architecture) of the power supply network;
  • Methodologies for evaluating various power feeding systems such as the conventional DC system, AC system provided by commercial power networks, and Higher Voltage DC system are:
      1) Methods for evaluating performance of the system;
      2) Calculation (or estimation) method for obtaining an environmental effect of the system, validity of the energy supply system to the ICT equipment, etc.

The work under this question could provide the basis for L-series Recommendations on power feeding systems.


Tasks include, but are not limited to:

  • A new Recommendation on the characterizations and specifications of the power feeding system, especially for the DC system;
  • A new Recommendation on the system configuration, architecture, and cable distribution of the power feeding system;
  • A new Recommendation on methodologies for evaluating the performance of energy feeding systems and their environmental impact.
  • A new study on enabling use of renewable and alternative energy sources;
  • A new study on the coordination of renewable energy and DC interface;

 An up-to-date status of work under this Question is contained in the SG 5 work programme (use URL as shown in the table below)




  • K-series


  • 4, 5, 6, 9, 12, 17 and 18/5

Study Groups:

  • ITU-T SGs 9, 13, 15, and 16
  • ITU-D SGs
  • ITU-R SGs

Standardization bodies: