The situation of complete transient protection and the cause of the electric shock stress of the gro

　　The situation of complete transient protection and the cause of the electric shock stress of the ground voltage

　　Full transient protection condition

　　One of the main causes of high-voltage transients is the direct or indirect lightning effect of the external power supply system. Regardless of the cause of the transient, whether it is a direct lightning hitting the line or the induction effect of a nearby lightning, the initial stress attenuation is caused by the flashover between the various points in the entire power distribution system or between the line and the ground. .

　　The result of these flashovers is that the transients appearing between the power line and the ground line become common mode when they reach a remote location. Even if the neutral line is connected to the ground near the building entrance, the transient stress can become common mode at the protected equipment because of the flashover on the cables, switchboard junction boxes and sockets in the building. Flashover alleviates the stress between category A and category C places. As a result, the transient suppressor that only provides protection between the live line and the neutral line does not provide protection for the equipment and common-mode capacitors for stress situations between line-to-ground and neutral-to-ground.

　　Reasons for the electric shock stress of the grounding voltage of the power adapter of small household appliances

　　The voltage stress that appears between the power line and the ground loop is called the common mode transient voltage. When a common-mode transient voltage reaches the suppressor, the current flows to the ground through one or several transient suppression devices. As a result, a considerable current will flow through the ground terminal during transients. Because there are resistance and inductance between the transient suppressor and the user's access line, this kind of ground current can increase the potential of the local system ground compared to the actual ground. Therefore, the shell of the protected device is different from the real ground. There is a danger of electric shock. This voltage is called ground voltage.

　　Therefore, there may be controversy that the transient suppressor returning stress current to the ground is a shock hazard and should not be used. This argument is only feasible when it is ensured that the load will not break down to the ground during the stress period of the transient suppressor. In fact, the equipment may malfunction in this mode, even without the suppressor, the ground voltage is shocking. The danger still exists. In addition, if the load is not protected if the suppressor is not used, it may be completely damaged.

　　It should be considered that the possibility of ground voltage shock under high-voltage stress conditions is unavoidable with or without transient protection. Measures should be taken to ensure that the resistance of the ground path is very small to reduce the ground voltage. If an operator approaches the equipment, all equipment that the operator can reach must be connected to the same ground loop. In the computer room, proper grounding is required, including the equipment and the building itself.

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