Because the building intercom in the access control system is installed outdoors, it is relatively vulnerable to lightning, resulting in equipment damage, economic losses and inconvenience to users. What lightning protection measures can we take? Don't worry. Let's learn about lightning first. Lightning strikes are generally caused by direct lightning and inductive lightning. Direct lightning is a strong discharge between charged cumulus and ground targets. The voltage peak can usually reach tens of thousands of volts or even millions of volts. It directly hits the equipment and has amazing destructive power. High buildings and their sides are vulnerable to direct lightning. Induction mine is divided into two types: electrostatic induction mine and electromagnetic induction mine. 1. Electrostatic induction lightning is caused by a large amount of charge induced on the top of overhead line conductor or other conductive protrusions when the charged cumulus is close to the ground. It will produce a high potential. The lightning rod, lightning strip, lightning wire, lightning network or metal objects are usually used as lightning arresters to receive the lightning current, guide it to the grounding device buried in the ground and dissipate it into the ground through the metal conductor as the downlead. 2. Electromagnetic induction lightning is caused by the rapid change of strong magnetic field in the surrounding space caused by huge impulse lightning current during lightning discharge. This rapidly changing magnetic field can induce a high electromotive force on adjacent conductors. If the electromagnetic energy caused by lightning induction is not discharged into the ground in time, it may produce discharge sparks, causing fire, explosion or electric shock. Induction lightning is not as violent as direct lightning, but it occurs more frequently and causes greater harm to the equipment. This is because direct lightning only causes disasters to the ground when lightning clouds flash to the ground, while induction lightning may cause disasters regardless of lightning clouds flash to the ground or between lightning clouds. A lightning flash can induce Lightning Overvoltage in a large range and multiple small parts at the same time, and this induced high voltage can be transmitted far away through metal wires such as signal line, power line and telephone line, resulting in the expansion of the scope of lightning damage. Well, through the above analysis of lightning stroke, we can take the following measures to prevent it. 1. The installation position of the power box shall be selected correctly. (1) avoid installation on the side wall around the house, especially on the side wall protruding from the house, so as to prevent direct lightning attack. (2) avoid installation on the wall on one side of metal water pipe, gas pipe and other pipes, especially on the same side wall less than 5m away from metal water pipe and gas pipe. 2. Grounding measures shall be taken for power box and circuit board, the grounding wire shall be firm and reliable, and the grounding resistance shall be ≤ 0.1Ωã 3. Wiring shall be correct and reasonable. The power line and signal line shall be laid indoors. Outdoor wiring shall be avoided as far as possible, and the same direction and cross wiring with metal water pipe, gas pipe and other pipes shall be avoided. If it is impossible to avoid the same direction wiring with metal water pipe, gas pipe and other pipes, the distance between them shall be ≥ Five meters. The wiring shall be straight and the bending wiring shall be minimized. 4. The power supply of the power box shall be connected to the power socket. When lightning may occur due to weather prevention or weather change, it is convenient to cut off the power supply in time to prevent lightning.