YD/T 944 is a Chinese telecommunications industry standard that specifies the lightning protection requirements and the test methods for telecommunication power supply equipment. The equipment it governs is the rectifier, the direct current distribution unit and the associated control and monitoring apparatus that supply a telecommunications station, and the standard reflects the position that equipment occupies: it is connected to an alternating current supply that arrives from outside the building, and it delivers a direct current supply to equipment that is itself connected to subscriber or trunk cables leaving the building, so a surge can reach it from either side. The standard sets the location and arrangement of the protective devices within the equipment, the withstand requirements on each port and the tests by which they are verified, and it defines the criteria for continuing to operate and for surviving without damage. It is applied alongside the industry codes for earthing and for the protective devices installed at the distribution board.