Discussion on lightning protection and grounding o

On lightning protection and grounding of weak current engineering in intelligent buildings (2)

III. cable connection this compact machine can use various plastic materials to produce particle and fragment ground

in the entrance area of buildings, the wiring room on each floor of high-rise buildings and each secondary junction room should be equipped with grounding devices, and the grounding devices in the entrance area of buildings must be located at or as close to the protectors as possible. The shielding layer of the trunk cable must be welded to the grounding device of the wiring room or secondary exchange room where the trunk cable passes by 4mm2 stranded copper wire, and the shielding layer of the trunk cable must be continuous

the shielding layer of the building incoming cable must be welded to the grounding device in the entrance area of the building

the grounding wire between each wiring room or secondary connection room shall be welded with a multi strand copper core grounding bus, and then connected to the grounding body. The grounding wire should be located in the center of the building as far as possible. There are many application equipment placed in the wiring room and equipment room with relatively large area. The grounding wire should adopt the grid method to make the wiring room or equipment room equipotential as much as possible. Unshielded trunk cables shall be placed in metal trunking or metal pipes. The metal trunking (pipe) joint shall be firmly connected to maintain electrical connection, and the wiring room through which it passes shall be connected to the grounding device with 6mm2 braided copper tape

the grounding resistance value should be determined according to the equipment grounding requirements of the application system. Generally, the resistance value should not be greater than 1 Ω. When there is strong electromagnetic field interference in the application equipment or adjacent to the generic cabling connection, and higher requirements are put forward for the grounding resistance, the minimum value should be taken as the design basis

the design of grounding device can refer to the relevant provisions of the national standard GB "Regulations on the design of electronic computer room". Each secondary junction room of high-rise buildings shall be equipped with grounding devices. On the grounding device at the entrance of the building, the shielding layer of the entrance cable and the ground plate of the protector are welded together with 5mm diameter multi strand copper core wire. In the floor distribution room, the shielding layer of the cable must be connected to the qualified grounding terminal of the distribution frame (cabinet). When the shielding layer is indirectly grounded in the wiring, multi strand copper core wire with a diameter of 4mm shall be used to weld the shielding layer of the cable to the qualified indirect grounding end of the wiring where it enters or leaves the shielded cable. The grounding wires of each floor wiring room or secondary connection room are welded to the grounding bus respectively. A single point grounding mode in which a single point of grounding wire is connected to the grounding body by the grounding bus. The connecting wire from the wiring room of each floor to the grounding bus shall be multi strand braided copper core wire, and the connection distance shall be shortened as far as possible. The grounding bus of high-rise buildings should be located in the central part of the building as far as possible

IV. distribution frame (cabinet) grounding

the grounding terminal of each floor distribution frame should be reliably connected to the grounding device in the wiring room

the DC resistance of the grounding conductor from the floor distribution frame to the grounding electrode shall not exceed 1 Ω, and it shall be permanently connected

each floor distribution frame (cabinet) should be connected to the grounding electrode in parallel, and should not be connected in series

if there are multiple different grounding devices in the application system, these grounding electrodes should be connected with each other to reduce the potential difference between gb3142 (8) 2 of the grounding devices

the metal trunking or metal pipe of wiring should be grounded to reduce impedance

v. requirements for connecting cables of the grounding body

within 30m from the grounding body, the grounding conductor uses a 4mm Diameter multi strand copper cable wrapped with an insulating sleeve

if the distance from the grounding body is more than 30m, the diameter of the grounding cable should refer to the values in the table below

each distribution frame (cabinet) in the distribution room should be reliably connected to the grounding bar of the distribution frame (cabinet), and its grounding wire should be greater than 2.5mm2, and the grounding resistance should be less than 1 Ω

VI. composition of weak current special grounding system

1 Ground wire: the ground wire is made of rectangular copper (40 × 4) Row connection assembly. The wiring direction is according to the wiring system of the building. All instruments and equipment requiring anti-static interference are reliably connected through copper core wires, so that the whole system forms an independent anti-static and anti-interference system. (as shown in Figure 1)

2 Grounding body: the artificial grounding body can be made of steel pipe, round steel, angle steel, flat steel, etc. at the same time, in order to increase its conductivity and improve its anti-corrosion ability, galvanized materials can be used on the surface. Its installation method is shown in figure 2:

(1) the length of grounding body is 2.5m galvanized angle steel (45 × 45) quantity: 3 pieces

(2) bury vertically in horizontal or rake shape

(3) the spacing of angle steel is 2.5m-3m

(4) buried depth ≥ 0.6m

(5) the vertical grounding body can be welded with galvanized flat steel to form a whole. If the outgoing line of the grounding body and the ground wire are connected with gongs and nails, they should be firm and reliable, and the contact should be treated with anti-corrosion treatment

(6) in order to increase the conductivity of the grounding body, the resistance of the sealing environment of the grounding body can be reduced. Lime, salt, water, ligneous acid, metal chips and other materials can be prepared in proportion for watering

3. Anti static and anti-interference grounding scheme:

(1) set four grounding bodies around the building structure

(2) set a detection point at the connection between each grounding body and the ground wire

(3) the four grounding bodies are reliably connected with the ground wire to connect the whole grounding system into a system

4. The anti-interference ground wire is the low-level signal of the equipment system. At the same time, for the sake of safety, it is necessary to set a safety ground wire to prevent the shell 1: the serial port is set with faults, and the induced electricity will harm the human body, but pay attention to its wiring method (as shown in Figure 3): 1) the inner shell and the shell are connected together by metal parts, and the shell and the grounding body are connected by metal parts, which must be reliable and durable

(2) the anti-interference signal ground, including the shielding wire, must be separately connected with the grounding body