Q: I am an employee of Jiande City Lightning Protection Equipment Inspection Institute. I have a question for you.

Now our civil air defense office has installed an air defense siren, the principle of which is that an electric motor generates sound after it rotates. I don't know if I usually don't use the alarm, that is, turn off the air switch, so that it will be damaged by the lightning current coming from the power line, and whether it is necessary to install a power supply arrester.

Hereby consult, please reply.

 

A: In general, most of the lightning electromagnetic pulses (LEMP) produced by lightning strike through metal wires, and the power line is the main conductive line. If the circuit breaker is used to disconnect all lines that may conduct overvoltage, it should be said that the problem is not great if SPD is not installed. Who has heard that the TV opportunity in the box was struck by lightning? However, the general switch only disconnects one end (or three ends) of the phase line, and there will still be overvoltage intrusion on the neutral line (zero line). This is the difference between the MCB and the general switch.

In addition, the anti-aircraft alarm is probably installed on the roof? It should be within the protection range of the air-termination device, and the metal shell should be equipotentially connected to the lightning protection belt on the roof.

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June. 22, 2020