Lightning protection measures for electronic and security equipment in buildings

Late July to early August is the season of frequent summer thunderstorms. The Beijing Lightning Arrester Safety Inspection Center announced in this year's annual inspection of lightning protection that the pass rate of direct lightning strikes on buildings in the city reached more than 90%, while the pass rate of indirect lightning strikes on electronic systems in buildings was less than half. In recent lightning disasters, more than 80% of them were internal equipment including electrical appliances, monitoring systems, and probes that were damaged. Some high-tech electronic equipment has weak anti-interference capabilities and is most likely to be "injured" during thunderstorms. For example, some residential communities have no lightning protection devices at all for monitoring probes, intercom systems and other facilities. Induction lightning can easily take advantage of the situation and destroy the system. In fact, these high-tech electronic systems must have special protection, such as installing electromagnetic shielding devices and overvoltage protection devices to prevent lightning electromagnetic pulses and internal operating overvoltages from damaging electronic equipment.

Modern security monitoring products are all microelectronic products. Monitoring equipment has the characteristics of high density, high speed, low voltage and low power consumption. It is very sensitive to various electromagnetic interferences such as lightning overvoltage, power system operation overvoltage, electrostatic discharge, electromagnetic radiation, etc., which makes the monitoring system equipment very vulnerable to lightning/overvoltage damage, the consequences of which may cause the entire monitoring system to fail to operate, and cause inestimable economic losses and safety risks. The entire monitoring system is widely distributed, the lines are long, and it is easy to be damaged by induced lightning. Therefore, the equipment at both ends of the transmission line, including the camera part, the optical terminal part of the branch room, and the LAN remote access part, are the key parts of lightning protection. Each functional equipment must take measures such as power supply lightning protection, signal lightning protection, and grounding to ensure safety.

Common problems in installing lightning protection equipment in monitoring systems?

1. The grounding resistance is too large or there is no grounding. The "Video Security Monitoring System Engineering Design Specification" and the "Building Information System Lightning Protection Technical Specification" do not clearly stipulate the grounding resistance of the monitoring system lightning protection. Generally, the grounding resistance of the monitoring system is designed according to the resistance of the computer room and the grounding resistance of the information system: the independent grounding resistance is not more than 4 ohms, and the combined grounding resistance is not more than 1 ohm. Specifically, the grounding resistance of the monitoring system can be appropriately increased according to different geological conditions. For example: in the forest fire prevention unit, the camera must be installed on the ridge, the address is bluestone, there are no rivers and ditches within 200 meters, and there are no large gravel and soil areas that can be excavated. At this time, if the grounding of the monitoring system in this specific place is required to be no more than 4 ohms, the cost is ten times or even dozens of times that of the monitoring system itself, then choose to increase the grounding resistance appropriately and use cables with large flow as the connecting ground wire.

二、无直击雷防护措施，这种情况比较常见的是枪机摄像机，有人认为已将安装了三合一信号避雷器，接地也做好了，应该没有问题了，可是却不知道避雷器是防雷传导雷、感应雷的工具，对于直击雷没有任何的作用。雷电对电子信息系统的损毁一般有几种手段：1、机械效应，例如雷击大树，有时候会把大树的支杆击断，主要靠得是雷击的机械效应。2、热效应，雷击点的瞬间温度可以达到3000度以上，使金属瞬间鎔化。3、电磁效应，这是一个无形的杀手，它功过电磁感应产生瞬间强电流烧坏设备。直击雷防护只要使靠避雷针这个设备，改变了雷电的运行方向，使雷电不大可能直接击中监控器。还有一种情况使使用曲杆球机的竟然安装避雷针，这种情况的金属杆本身已将将球机保护起来，没有必要在增加成本，安装避雷针。

3. The signal lightning arrester is too far away from the equipment to be protected. If the lightning arrester is installed too far away from the equipment, there is no way to eliminate the lightning current induced on the communication line and power line from the arrester to the front end of the equipment. Therefore, it is recommended that the signal lightning arrester should be installed directly at the front end of the monitoring equipment, especially where the signal power line is obvious.

Fourth, the problem of grounding cables. In order to save costs, metal rods are often used as down conductors of the working grounding system. Let’s not talk about “right” or “not” for now. According to the design, metal rods are generally used as down conductors of the direct lightning protection system. At this time, the working ground is connected to the metal rod. When there is a direct lightning strike, there is no voltage difference between the front end of the signal lightning arrester and the metal rod body. In other words, your direct lightning will directly impact the signal lightning arrester or power lightning arrester, which will cause the lightning arrester to age prematurely or be damaged on the spot. Therefore, it is recommended that the down conductor of the working ground should be connected separately.

5. The selection of three-in-one surge protector (or BNC surge protector), according to the specific market conditions and installation experience, BNC signal electrophoresis protector is set within the lightning protection range for a long time, which is far from enough for the protection of the monitor. For the monitor, there are also surges, spikes, burrs, etc., which may be caused by the start or shut down of large-scale power tools nearby, and changes in the nearby electromagnetic field, etc. These not only require the protection of varistors or discharge tubes, but also a logic filter circuit to provide a safer power environment for the monitor. The latter factor was ignored.

Lightning protection is a relatively complex issue. The lightning protection design of the security monitoring system not only depends on the performance of the lightning protection device, but more importantly, before the design and construction of the monitoring system, it is necessary to consider the geographical environment of the monitoring system and design appropriate cable laying, shielding and grounding methods. In short, the lightning protection design should be considered comprehensively to achieve good results.