YD/T 1235.2 is a Chinese telecommunications industry standard that defines the test methods for the surge protective devices installed in the low voltage distribution system of a telecommunications station or office. The corresponding Chinese practice has been shaped by the way the network is built: the alternating current supply enters a station over a cable that may run outdoors for some distance, the station it feeds carries a very large number of subscriber lines that all leave the building, and the earthing system of the station is shared with the equipment. A device installed at the incoming distribution board therefore protects not only the power equipment but indirectly the communications equipment that shares the earth reference. The standard specifies the tests by which the characteristics of the device are established, including the impulse current withstand, the residual voltage, the response behaviour and the behaviour under a temporary overvoltage, and it is the companion to the part that states the requirements.