Guidelines for power-supply systems for datacom equipment in NTT

This paper describes the guidelines for power-supply systems for datacom equipment in NTT that were established at the beginning of 2002, to prevent accidents in power-supply systems. The guidelines indicate that the -48 VDC power-supply system is preferable for supplying power to the datacom equipment. They specify that the input capacitor in a DC-DC converter used in datacom equipment should have a value of at least 0.3 μF/W and that a capacitor should be connected to the input of the power distribution frame to prevent the oscillation in a -48 VDC system. They also prescribe that a pre-charge circuit should be installed to prevent inrush current to datacom equipment. If power-supply systems for datacom equipment follow these guidelines, there will be fewer serious accidents.