Lightning strikes into buildings and utilities are dangerous to people, utilities, structures and their contents. These risks entail the need to set up a package of protective measures. Comprehensive lightning protection is addressed in a set of standards EN 62305-1 to 4. In addition to a number of other areas, it includes important recommendations for the protection of telecommunications lines. In our applications, it is mainly the protection of data UTP / FTP lines, power cameras and data storages.
The basis of protection against damage caused by lightning strikes is the calculation of the risk of damage according to EN 62305-2. Based on the risk assessment, the building is classified into one of four classes lightning protection.
Typical Division of Objects into Classes:
- LPL I - hospitals, banks, waterworks, power plants, including nuclear ones, explosives warehouses;
- LPL II - schools, supermarkets, weapons depots, cathedrals, GSM transmitters;
- LPL III - family houses, agricultural buildings;
- LPL IV - buildings without the presence of persons and internal equipment, buildings only with high-current electrical installations.
LPL is abbreviation for "Lightning Protection Level", which must correspond to the design of the LPS "Lightning Protection System".
Based on the classification of the object into the class, it is determined how the protection of the object against lightning must be dimensioned. In applications typical of our equipment, it is especially necessary to ensure the installation of a protected system within the zone LPZ 1 or higher (EN 62305-1, paragraph 8.4.2). We achieve this by installing switches, PLCs and IO modules in steel cabinets series OH4320, OH6425, OH8625. The cabinets itself can be installed in the LPZ0B zone.
For easy comprehension of this text, the most typical ways of installing our devices are described below.
PoE Camera Installed on a Pole
When installing on free-standing poles, the biggest problem is probably to meet the above-mentioned requirement for installation of a protected system inside the LPZ 1 zone. For our supplied equipment (industrial switches, PLC and IO modules) it is sufficient to use OH cabinets with overvoltage protection at inputs.
||Overvoltage Protection in OH Cabinets
||EN62305-1 ed 2
|Intake 230 VAC
||12,5kA in the wave 10/350µs
||10kA in the wave 10/350µs (table E.2)
|Cable from Camera
1kA in the wave 8/20µs
- protection OVP-100M-HIPOE
- FE ports PP switches
0,16kA in the wave 8/20µs (table E.3) for an indirect blow to the building. The protected system, including the camera, is located in zones LPZ0B - LPZ1, therefore a direct strike is not considered.
Another, indispensable part of the system is the camera and the cable between the camera and the cabinet. There is an unsolvable problem with choosing the right type. Why? Especially cheaper camera models have plastic covers without any protection against electromagnetic fields. In the best case scenario, the camera has a cover made of aluminum alloy, which protects the electronics only against the electric field of the discharge. Surge protectors located in the cabinet do not protect the camera. For this reason, it is advisable to install OVP-100M-HIPOE (PoE camera) or OVP-100M/24-BOX (24VAC power supply) in the immediate vicinity of the camera. Use the cable between the camera and the camera with STP. When the shield is connected correctly, it reduces the induced overvoltage.
PoE Camera Installed on the Outside of the Wall
When designing an IP CCTV system with PoE cameras on the external walls of buildings, pay attention to their correct location. We recommend coordinating the design with the designer of the collection system. It decides on the location of collectors and especially leads, which may interfere with the planned location of the cameras. In any case, the following principles must be observed in these situations:
1. Cameras, including power cables, must be placed in the LPZ0B zone, protected from direct lightning strikes.
2. Cameras, including supply cables, must have a sufficient distance from the capture system.
To determine the sufficient distance from the collection system, use the formula s = Ki * (Kc/Km) * l given in the standard EN 62305-3 ed. 2.
Ki - coefficient depending on the selected lightning protection class (LPS), see Table 10 in EN 62305-3 ed. 2,
Kc - coefficient depending on the current flowing through the drains, see Table 12 in EN 62305-3 ed. 2,
Km - coefficient depending on the material of insulation used, see Table in EN 62305-3 ed. 2,
l - length in meters along the sump or drain to the nearest point of equipotential bonding.
3. All metallic cables leading from the camera to the building (interface of zones LPZ0B to zone LPZ1) must protect suitable surge protectors. As a guide, when choosing a suitable surge protection, we recommend using table E3 in ČSN EN 62305-3 ed. 2. It lists the expected currents for different situations. With the correct design of the collection system and keeping the distance from it, the data cable from the camera is in danger of damage type S4 with a maximum expected current of 160 A (8/20µs) for data cables and 5kA (8/20µs) for power cables. We recommend installing the data cable with overvoltage protection OVP-100M-HIPOE. Surge protection protects all 8 conductors up to 1kA in an 8/20µs wave. Another important detail is the two-stage design of the protections. Thanks to it, on the output is only low residual voltage in data pairs 1-2 and 3-6, which is important for effective protection of connected devices. See the picture below from the test when a pulse with a voltage of 2kV (1.2/50µs) and a current of 1kV (8/20µs) was applied between wires 1-2.
An even better solution is to replace metallic data cables with optical cables. In this case, we recommend installing miniature media converters 200M-1S.0.1-BOX-PoE directly with the cameras with integrated 1kA overvoltage protections in the 8/20µs wave. In this case, we can offer the delivery of media converters, including the OH3215 or OH4320 cabinets. Cabinets are certified and manufactured according to the requirements of the EN 61439-1 standard. They include, depending on the selected type of overvoltage protection III or I + II.
We recommend installing particularly important devices in a server room belonging to the LPZ 2 zone. It is suitable to separate the server room from the surrounding space by a spatial shield connected to the earthing system of the building, to install overvoltage protections of the 3rd degree at the interface with the LPZ 1 zone and to cover the floor with electrostatically conductive covering. Based on long-term experience, we do not recommend connecting the LPZ 2 zone with the LPZ 0 zones with metal data cables, even if they are equipped with surge protectors.
Updated: 07. 03. 2020