UL1449 5th Edition Section 41.7: Nominal Discharge Current Testing for SPDs

Section 41.7 of the document details the requirements for the nominal discharge current testing for Type 1 and Type 2 Surge Protective Devices (SPDs) and their component assemblies. Manufacturers must declare the nominal discharge current (In) value for testing, with options including 10 kA or 20 kA for Type 1 SPDs, and a broader range of 3 kA, 5 kA, 10 kA, or 20 kA for Type 2 SPDs. The testing ensures that the SPD can handle the specified In value, with adjustments made to the surge generator voltage to achieve the desired current through the SPD. The waveshape of the surge is allowed a degree of deviation from the initial 8 x 20 µs calibration, provided the front time does not exceed 9 µs, and the duration is at least 16 µs. This flexibility accommodates the practical variations encountered in testing SPDs in circuit configurations.

Further elaboration on the test setup includes applying the surges to the SPDs in an unenergized state, divided into three groups of five surges each, with specific intervals for applying the manufacturer's specified maximum continuous operating voltage (MCOV) and rest periods between each group to simulate operational stress. The document also addresses exceptions for SPDs that can conduct follow current, such as gas tubes and air gap devices, specifying a method for incrementally applying surges at different angles on the AC waveform. This detailed testing procedure is designed to verify the SPD's capability to withstand nominal discharge currents without failure, ensuring reliable protection against transient voltages and currents.