1. Distinguish AC/DC; DC high voltage is easier to arc, and sufficient margin is reserved for model selection; 2. Type selection of withstand voltage: working voltage × 1.5 ~ 2 times of margin, do not use the upper limit; 3. Confirm the load: resistive/inductive; the inductive load must be significantly derated; 4. Distinguish the demand: whether the PCB patch is directly inserted or the high-voltage cable needs to be led out (> 10kV is mostly lead type); 5. In humid environment, the model with lengthened edge and complete epoxy encapsulation is preferred.