Firstly, one should accurately understand the system composition of the security monitoring system. Then, accurately analyze the main reasons for the damage caused by lightning strikes to the security monitoring system and the possible invasion routes of lightning-induced overvoltage. Based on this, select appropriate lightning protection devices, study and explore the reasonable layout of signal and power lines, clarify the shielding and grounding methods, and thus provide an accurate and systematic lightning protection solution. This can effectively enhance the anti-lightning overvoltage interference ability of the security monitoring system and optimize the overall lightning protection level of the system.

I. Overview

With the development and progress of society, the continuous improvement of people's living standards, and the increasingly active social economy, the demand for "safety" has become higher and higher. The security monitoring system has been more widely popularized and applied. It is increasingly common in various industries such as highways, financial systems, military units, traffic monitoring, important places, various residential areas, public places, warehouse management, etc. At the same time, the security of the security monitoring system itself has also become a new and important issue.

Modern security monitoring products are all microelectronic devices. These monitoring equipment have characteristics such as high density, high speed, low voltage and low power consumption. They are highly sensitive to various electromagnetic interferences such as lightning overvoltage, power system operation overvoltage, electrostatic discharge, and electromagnetic radiation. This makes the monitoring system equipment extremely vulnerable to lightning strikes/overvoltage damage. The consequences may cause the entire monitoring system to malfunction and result in unpredictable economic losses and safety risks. In order to provide accurate and effective lightning protection solutions for security monitoring systems, we should first accurately understand the system composition of the security monitoring system, and then accurately analyze the main reasons for the damage caused by lightning strikes to the security monitoring system and the possible invasion routes of lightning overvoltage. On this basis, select appropriate lightning protection devices, study and explore the reasonable layout of signal and power lines, clarify the shielding and grounding methods, and then provide an accurate and systematic lightning protection solution. Effectively improve the anti-lightning overvoltage interference ability of the security monitoring system and optimize the overall lightning protection level of the system.

II. Overview of the Composition, Classification and Lightning Protection of Security Monitoring Systems

2.1 Composition of the Security Monitoring System

The security monitoring system usually consists of the following three parts:

Front-end part: It is mainly composed of black-and-white (color) cameras, pan-tilt units, protective covers, supports, etc.

Transmission section: Audio, video, control signals, and power supplies (both AC and DC) are transmitted using coaxial cables, wires, multi-core cables, and are laid overhead, buried underground, or along walls.

Terminal section: It is mainly composed of control equipment, picture splitter, monitor, video storage device, etc.

2.2 Classification of Security Monitoring Systems

According to the transmission methods of the transmission part, the security monitoring system can be mainly classified into the following categories:

A coaxial cable transmission monitoring system: Lightning protection focuses on the protection of the line interfaces at both ends of the transmission cable and the protection of the transmission cable itself.

B Twisted-Pair Transmission Monitoring System: The key points of lightning protection lie in the power protection at the front end and the terminal, as well as the protection of the twisted-pair interface.

C optical cable transmission monitoring system: The key points of lightning protection lie in the protection of the power supply at the front end and the terminal, as well as the protection of the shielding layer and reinforcing ribs of the optical cable itself.

D microwave transmission monitoring system: The key point of protection lies in the direct lightning protection of the wireless equipment at both the front and rear stations.

2.3 The main reasons for damage to the security monitoring system caused by lightning strikes

2.3.1 Direct Lightning Strike

A. Lightning struck the outdoor camera directly, causing the equipment to be completely damaged.

B. Lightning strikes directly on the cables, causing them to melt and get damaged.

2.3.2 Lightning Wave

When the power lines, signal transmission lines or other metal cables entering the monitoring room are struck by lightning or induced by lightning, the lightning waves will invade the equipment through these metal conductors/conductors, causing high potential differences that damage the equipment.

2.3.3 Lightning Induction

Electromagnetic Induction: When there is lightning strike flashover in the nearby area, a powerful transient electromagnetic field will be generated around the lightning strike path. The monitoring equipment and transmission lines located in the electromagnetic field will induce a large electromotive force, which may cause damage and destruction to the equipment.

Electrostatic induction: When there is an electrified thundercloud, opposite bound charges to the thundercloud will be induced beneath buildings and on transmission lines. This induced charge can reach up to 100kV on low-voltage overhead lines and 40-60kV on signal lines. Once the thundercloud discharges, the bound charges will rapidly spread, causing induced lightning strikes.

The lightning strikes caused by electromagnetic induction and electrostatic induction are both called induced lightning, also known as secondary lightning. It does not cause as much damage to equipment as direct lightning strikes do, but it occurs much more frequently. Statistics show that induced lightning strikes account for more than 80% of modern lightning accidents.

2.3.4 Ground Potential Transient

The direct lightning protection device (lightning rod) generates extremely high instantaneous voltages on its down conductors, grounding bodies, and the connecting metal conductors when it channels the powerful lightning current into the ground. This causes a significant potential difference between the nearby metal objects, equipment, lines, and human bodies that are not connected to them. The electric shock caused by this potential difference is known as ground potential rebound. Such rebound can not only damage electrical appliances and equipment, but also cause personal injury or fire and explosion accidents.

III. Key Points, Common Questions and Precautions for Lightning Protection Solutions for Security Monitoring Systems

3.1 Lightning Strike Protection

Direct strike protection is an indispensable and crucial foundation for lightning protection, and it is an indispensable component of lightning protection.

3.1.1 Direct lightning protection for front-end equipment

The front-end equipment of the security monitoring system comes in both outdoor and indoor versions. The equipment installed indoors is generally not exposed to direct lightning strikes. However, the equipment installed outdoors is mostly located in relatively open areas, where the risk of direct lightning strikes is higher. Therefore, direct lightning protection must be considered.

The front-end equipment of the security monitoring system, such as cameras, should be placed within the effective protection range of the lightning arresters (lightning rods or other lightning arrestors). For the front-end equipment that is already within the protection range of other lightning arresters or the original lightning protection system of high-rise buildings, generally, direct lightning strike protection need not be considered separately; for the front-end equipment that is not within the protection range of any lightning protection system, direct lightning strike protection should be considered. From a technical and economic perspective, installing an independent lightning rod for the direct lightning protection of the front-end equipment is not feasible. Generally, a lightning rod is erected on the support pole of the camera, and the down conductor can directly use the metal pole itself (or a Φ8 galvanized round steel or 30×3 galvanized flat steel), but to prevent electromagnetic induction, the power lines and signal lines of the camera along the pole should be laid in metal pipes, and the metal pipes should be reliably grounded.

3.1.2 Protection against Direct Lightning Strikes on Transmission Lines

To protect the transmission lines from direct lightning strikes, they should be avoided from being laid overhead. It is preferable to bury them through metal pipes, and both ends of the metal pipes should be reliably grounded.

3.1.3 Lightning Protection for Terminal Equipment

The building where the terminal equipment room (commonly referred to as the monitoring room) is located should take measures to prevent direct lightning strikes. A lightning protection belt made of φ10 round steel (coated with silver powder paint) can be constructed on the roof. Additionally, φ10 round steel can be used as the support for the lightning protection belt, with a support height of 15 cm. One support should be set every 1 meter, and 40×4 mm galvanized flat steel can be used as the down conductor to connect with the grounding grid (the grounding grid resistance should be less than 10 Ω). The spacing of the down conductors should not exceed 25 meters. Alternatively, a lightning rod can be used as a measure to prevent direct lightning strikes. A 40×4 mm galvanized flat steel can be used as the down conductor to connect with the grounding grid. The height and installation position of the lightning rod should be calculated according to the method.

3.2 Lightning Protection and Grounding System

All lightning protection systems must have reliable and effective grounding. The grounding system is also one of the essential components of lightning protection.

The front-end and terminal equipment of the security monitoring system should all have good lightning protection grounding, and the corresponding grounding system should comply with the specification requirements. Generally, the front-end equipment that is independent of the building where the monitoring room is located must have an independent grounding. However, it is particularly important to note that: regardless of whether it is the front-end or terminal equipment, if the distance between the grounding systems is less than 20 meters, the two grounding systems should be connected in an equipotential manner.

3.3 Issues to be Noted When Installing Along the Wall

Many cable installers, due to their limited understanding of lightning protection knowledge or the simplicity and convenience of the drawings, are accustomed to bundling the outdoor wiring lines with the lightning protection strips and down conductors of the building. This approach simplifies the construction process and enhances the aesthetics, but it also brings significant lightning safety hazards. This is something that deserves attention and caution. To reduce the risk of lightning damage, any conductive wires or metal lines should be avoided from being parallelly bundled with the direct strike protection system as much as possible, and should comply with the relevant regulations.

3.4 Selection of Lightning Protection Devices for AC Power Supply

Effective lightning protection measures should be taken at all AC power input terminals of the security monitoring system. Additionally, it is necessary to ensure that the building where the equipment is located has a good lightning protection grounding system, and further confirm whether the lightning protection devices in the building are properly used.

Power surge protectors should be installed at the incoming power lines of the front-end equipment. Considering that the power systems of security monitoring systems are generally not very standardized, there is usually a few volts or tens of volts of voltage between the neutral and ground, sometimes even tens of volts or more. Moreover, when installing single-phase power surge protectors, installers usually do not pay attention to distinguishing between the neutral and live wires. Given this situation, we suggest that when choosing single-phase power surge protectors, it is advisable to avoid using products with the 1+NPE protection mode. Because if there is an AC voltage on the NPE module, when the NPE module acts, it will generate a power frequency continuation current, making it difficult for the NPE module to extinguish the arc and causing the NPE module to burn out.

The power lines entering the monitoring room should be subject to three-level protection. A first-level power surge protector can be installed at the power inlet of the main distribution room in the building. A second-level power surge protector can be installed at the power inlet of the distribution box on the floor where the monitoring room is located. A third-level power surge protector should be installed at the power inlet of the important equipment in the monitoring room. In cases where the zero and ground voltages are relatively high, it is not recommended to use power surge protectors with the 3+NPE or 1+NPE protection mode.

All lightning arresters should be reliably grounded.

3.5 Transmission Line Protection for Security Monitoring System

Statistical data show that over 80% of lightning damage incidents in security monitoring systems are caused by overvoltage from lightning intrusion waves induced on the lines connected to the system. Therefore, ensuring the protection of the lines connected to the system is an indispensable part of overall lightning protection.

The safest wiring method should be to lay the transmission lines fully through metal pipes and buried underground. At the same time, please note that both ends of the metal pipes must be effectively grounded. The transmission lines buried underground with metal pipes can significantly reduce the amplitude of lightning intrusion waves, thereby lowering the probability of equipment being damaged by lightning intrusion waves. In actual engineering, in many cases where conditions do not permit, the transmission lines can be fully laid on metal pipes and suspended overhead; or if not fully laid with metal pipes, they must be buried underground before entering the monitoring room and front-end equipment. The buried length should be no less than 15 meters, and at the  end， the metal outer skin of the cable， the metal pipe， and the lightning protection grounding should be effectively connected.

Appropriate lightning arresters should be installed at both ends of all transmission lines.

3.6 Protection of Optical Fiber Communication Lines

Generally speaking, optical fiber lines do not need to be equipped with lightning surge protection devices because optical fiber lines themselves are not conductors and thus cannot induce or transmit overvoltage surges. This is something that many people are aware of, but what is often overlooked is the lightning protection of optical cables. This can lead to some cases of lightning overvoltage flashover and damage to equipment. The main reason for this is that optical cables usually have metal reinforcing ribs and metal sheaths for protecting the optical cables. Although the optical fibers themselves do not induce or transmit overvoltage, their metal reinforcing ribs and metal sheaths are very prone to inducing and transmitting lightning overvoltage. They must be properly handled, that is, at the point where the optical cable enters the house, grounding protection must be done well.

3.7 Precautions for Lightning Protection of Video Signals

Video signal lightning protection is a relatively simple concept. However, it often happens that due to negligence in the working process, the lightning protection function fails, and as a result, the video lightning protection itself gets damaged.

Currently, most of the signal lightning protection products on the market generally adopt a two-level protection method. The first level serves as the coarse protection and usually uses gas discharge tubes as the protective device; the second level is the fine protection and generally uses TVS as the protective device. As a result, the signal lightning protectors inevitably have a distinction between the front and the back, as well as between the input and output ends. Because the current TVS used in the signal lightning protection circuits has very limited current-carrying capacity. If the connections of the front and back levels are reversed, once an overvoltage surge comes in, the TVS is very likely to be broken first, causing the lightning protector to be damaged or fail. And this situation occurs frequently in the market. Due to the fact that many lightning protection companies' salespeople are not familiar with this issue, when signing contracts, they often easily overlook the distinction between "negative input and positive output" and "positive input and negative output"; many lightning protection engineering companies' purchasing personnel also tend to ignore this issue, only ordering "video signal lightning protectors"; finally, when the products arrive at the site, the engineering personnel do not carefully consider or treat it seriously, just connecting them as long as they can be connected, ultimately resulting in some video signal lightning protectors being connected in reverse.

Now, Shanghai Leiyuan Electrical Appliance Co., Ltd. has newly launched a video surge protector. It adopts dual-level protection and has been registered for patent protection. It can effectively prevent the occurrence of the aforementioned problems. It is compatible with both "negative charge entering and positive charge exiting" and "positive charge entering and negative charge exiting", reducing the work pressure on salespeople and purchasers, making the work simpler, more convenient, and more conducive to the allocation and use of the video surge protector.

3.8 DC power supply protection, control line signal protection

The common problems in protection of DC power supply, control line signals and video signals are the same. The difference is that the connection methods for DC power supply protection and control line signal protection are generally crimping type, without "anode" and "cathode" distinctions, and thus there will be no problems such as wrong purchase or wrong delivery. However, on-site engineers must pay attention to correctly connecting such lightning protectors. Generally, the commonly used labels are: input (IN), output (OUT), or: surge terminal, protection terminal, also known as: remote end, near end. In other words, input (IN), the surge terminal, is also called the remote end, and should be connected to the end that is prone to introducing lightning overvoltage; output (OUT), the protection terminal, is also called the near end, and should be connected to the end of the protected equipment.

IV. Other Important Notes and Maintenance Guidelines

4.1 The lightning protection design should be based on a thorough investigation of geographical, geological, soil, meteorological, environmental conditions, as well as the activity patterns of lightning and the characteristics of the protected objects. It should then conduct a detailed study of the form and layout of the lightning protection devices.

4.2 In specific engineering projects, the installation locations of lightning protection equipment and the selection of equipment should all be determined by professionals based on the actual situation.