As the rainy season approaches, ensuring proper lightning protection for monitoring systems becomes a critical part of product performance testing. This article provides an in-depth analysis of the lightning protection design for security monitoring systems, covering various aspects from front-end equipment to terminal devices and grounding systems.
First, when it comes to direct lightning protection for front-end devices, there are two main types: indoor and outdoor. While indoor equipment is generally safe from direct lightning strikes, outdoor devices—often located in open areas—are more vulnerable. Therefore, they require careful consideration for direct lightning protection. Cameras and other outdoor equipment should be placed within the effective protection zone of a lightning rod or similar conductor. If the equipment is already within the protection range of an existing lightning system (such as on a high-rise building), additional protection may not be necessary. However, for equipment outside of any such system, direct lightning protection measures must be implemented.
From a technical and economic standpoint, installing independent lightning rods for every camera is not always feasible. Instead, lightning rods can be mounted on the camera’s support pole, with the downlead using the metal pole itself (e.g., 8mm galvanized steel rod or 30×4mm galvanized flat steel). To prevent electromagnetic induction, power and signal cables should be routed through metal conduits and properly grounded.
For grounding and lightning protection of front-end equipment, several key rules apply:
1. Outdoor cameras should be equipped with lightning rods that are positioned higher than the camera. The protection zone extends 45–60 degrees downward from the tip of the lightning rod. It's important to insulate the lightning rod from the camera’s mounting structure to avoid electrical interference.
2. Grounding for all front-end equipment should be connected to a centralized grounding bus at the end point to ensure no potential difference exists between ground points, preventing ground loops and possible damage.
3. Indoor cameras should be connected to a shared grounding terminal, and a non-fuse circuit breaker and leakage protector should be installed at the power input. A surge protector rated at 3000KV is also recommended where permitted.
4. After grounding outdoor surveillance cameras, the resistance should be tested to ensure it is less than 10Ω, and the grounding rod should be installed according to the standard three-point impedance test.
Next, for transmission lines, it's best to avoid overhead installations and instead use buried metal pipes, with both ends properly grounded to protect against direct lightning strikes.
For terminal equipment, such as the monitoring room, the building should have its own lightning protection system. This includes using 10mm round steel on the roof as a lightning protection zone, along with a 40×4mm galvanized flat steel as a downlead connected to the grounding network. The distance between downleads should not exceed 25 meters. Lightning rods can also be used, following the rolling ball method for height and placement calculations.
The entire lightning protection system requires a reliable grounding system. Front-end and terminal equipment must meet specified grounding requirements. If the front-end equipment is independent of the building housing the monitoring room, it should have its own grounding system. However, if the distance between the two grounding systems is less than 20 meters, equipotential bonding must be performed.
When selecting AC lightning protection devices for the security system, all power supply lines should be protected. The building’s existing lightning protection and grounding systems should be checked, and the correct installation of lightning protection devices verified. A primary surge protector should be installed at the incoming power line of the building, with secondary and tertiary protectors placed at the distribution box and critical equipment locations respectively. In cases where zero-to-ground voltages are high, it's advisable to avoid NPE protection modes due to the risk of arc failure.
Lightning protection for the monitoring room is often overlooked but is just as important. The room is the final line of defense against lightning-induced damage. The building should have lightning rods, conductive strips, or mesh networks to prevent direct strikes. Pressure equalizing rings should be installed, connecting all downleads, metal structures, and objects to the ring to reduce potential differences.
Although current protective measures can only mitigate damage from powerful lightning strikes, ongoing efforts by experts in the field aim to develop more advanced lightning protection solutions. With the growing number of security cameras, lightning protection technology is becoming increasingly important. We believe that as surveillance systems expand, lightning protection will become even more essential.
In the monitoring room, key equipment includes the central computer, video matrix, hard disk recorder, intercom system, and power supply. These devices should be placed in the most protected area of the building, avoiding the top three floors. If the building’s lightning grid does not meet anti-interference standards, a shielding layer should be added on the roof. Cables entering the building should be wrapped in metal tubes and buried at least 10 meters underground. If this is not possible, the length of the shielded pipe should be extended. Both ends of the metal tube and junctions between lightning protection zones should be bonded and grounded.
If the equipment has a metal casing, it should be directly connected to the equipotential bonding strip using the shortest possible wire. For non-metallic casings, additional shielding may be required if the building’s shielding does not meet electromagnetic compatibility standards. The shielding should then be connected to the equipotential bonding strip.
Finally, to minimize exposure to electromagnetic fields, monitoring room equipment should be at least one meter away from the building’s exterior walls. This helps prevent damage from strong electromagnetic fields generated around downconductors during lightning strikes.
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