The weak current system does not need me to explain and everyone understands it clearly. So how deep is your understanding of the weak current system? For example, what are the precautions for grounding of weak current systems? Let's focus on the grounding precautions for weak current systems!
Weak current system grounding
a: General Provisions
The grounding of the weak current system is divided into protective grounding and functional grounding according to the purpose. Protective grounding is divided into: anti-shock grounding, lightning protection grounding, anti-static grounding and anti-electrical corrosion grounding; functional grounding is divided into: working grounding, logic grounding, shielding grounding and signal grounding. Different grounding has different requirements, and the grounding construction should be determined according to the design.
The grounding device of the weak current system that needs to be grounded shall meet the following requirements:
1. When galvanized electric pipes are used for piping, except for the places clearly specified in the design, it is not necessary to bridge the pipes after connecting the pipes and the pipes and the metal boxes, but the following regulations should be observed:
1) When threaded connections are used between pipes, the length of the thread at the end of the pipe should not be less than 1/2 of the length of the pipe joint, the surface of the thread should be smooth, free of rust and defects, and the threads should be coated with electrical full grease or conductive anti-corrosion grease. After connection, the thread should be exposed 2~3 buttons.
2) When the pipes are connected by casings with set screws, the screws should be tightened; in vibration places, the set screws should have anti-loosening measures.
3) The connection between the tube and the box should not be made of plastic nano, but conductive metal nano should be used.
4) When there is a pe line in the weak current tube, each junction box should be connected to the pe line.
2. When the piping adopts galvanized electric pipes, and the design stipulates that the pipes need to be bridged, the following regulations should be observed:
1) The exposed piping should not be connected by fusion welding, but should be connected by the special next-line clip specified by the design.
2) Electric pipes buried in the ground or buried in concrete should not be bridged by line cards, but welded bridges can be used.
3) If there is bare soft PE copper wire in the tube, the electric tube can not be bridged. This pe line must be connected to every junction box it passes through.
3. When black iron pipes are used for piping, if the design does not require bridging, it is not necessary to bridging. If bridging is required, round steel can be used for bridging between the black iron pipes and between the black iron pipes and the junction box, and the length of the bridging should not be less than 6 times the diameter of the bridging round steel. When bridging between zinc bridges, a copper bolt should be welded at the end of the black iron pipe, and a copper wire of not less than 4mm should be used to connect the galvanized bridge.
4. When both strong and weak currents use pvc pipes, in order to avoid interference, weak current piping should be avoided to be laid in parallel with strong current piping. If it must be laid in parallel, the distance should be greater than 0.5m.
5. When the strong and weak currents are laid in wire troughs, the strong and weak wire troughs should be separated; when they need to be laid in the same wire trough, the strong and weak currents should be separated by metal separators.
b: Grounding of telecommunications equipment
1. In order to prevent external voltage from endangering personal safety and damage to equipment, suppress electrical interference, and ensure normal operation of communication equipment, the following parts of telecommunications equipment should be grounded:
(1) DC power supply, racks and casings of telecommunication equipment; metal sheath and shielding layer of human-station communication cables.
(2) The exposed conductive parts of power supply equipment such as AC power distribution panels and rectifier panels.
(3) The exposed part of the DC distribution panel.
(4) The exposed conductive part of the rack of the AC/DC dual-purpose telecommunication equipment and the power supply rectifier plate that is not insulated from the rack and the rack.
(5) Cables, overhead lines and related parts that need to be grounded, such as arresters, arresters, protective gaps, etc.
2. When the low-voltage power distribution system adopts the tn system for power supply, if the telecommunication equipment requires to strictly limit the interference of the power frequency AC to it, and the telecommunication equipment is not easy to be insulated from various golden metal components in the station, the tn-s system should be used; When the interference requirements are not too strict, the tn-c system can be used; when the leakage current of the telecommunication equipment is 10ma and above, the tn-s system should be used.
3. When the exposed conductive parts such as power distribution panel and rectifier panel are electrically connected to the rack and frame by the reinforcement device, they still need to be connected to the pe line or the pen line.
4. When the it system is used for power supply and the leakage current of the telecommunication equipment is more than 10ma, in order to avoid the malfunction of the protection equipment, a double-coil transformer can be used for power supply, the primary side is connected to the it system, and the secondary side is powered by tn system, At this time, the grounding of the power supply equipment is the same as that of the tn system.
5. The working grounding of telecommunications equipment is generally required to be set separately, and it can also share a grounding device with the working grounding of the transformer in the building. However, it must be connected to the grounding device through an insulated special grounding wire.
6. When a common grounding device is used for telecommunication equipment, its grounding resistance should not be greater than 1ω. It is advisable to use two copper core insulated wires with a cross-sectional area of not less than 25mm2 to be laid on the common grounding electrode. When the basic steel bar is used as the common terminal, there should be a copper-iron transition joint at the connection.
c: Grounding of electronic equipment
Signal grounding, logic grounding, power grounding, shielding grounding and protective grounding of electronic equipment generally share a grounding electrode, and its grounding resistance is not greater than 4ω; when the grounding of electronic equipment, power frequency AC grounding, and lightning protection grounding share a grounding electrode When the grounding resistance is not more than 1ω. If the shield grounding is set separately, its grounding resistance is generally 30Ω.
2. For electronic equipment with poor anti-interference ability, its grounding should be separated from lightning protection grounding, and the distance between the two should be more than 20m. For electronic equipment with strong anti-interference ability, the distance between the two can be reduced as appropriate, but should not exceed 5m.
When the electronic equipment grounding and lightning protection grounding use a common grounding device, in order to avoid the counterattack during lightning strikes and ensure the safety of the equipment, buried armored cables should be used for power supply.
3. The shielding layer of the cable must be grounded. In order to avoid interference current, the signal cable and the low-frequency cable below 1mhz should be grounded at one point; for the cable above 1mhz, in order to ensure that the shielding layer is at ground potential, multi-point grounding should be adopted.
4. In order to avoid the influence of loop current and instantaneous current, the radiation grounding system should use one-point grounding; in order to eliminate the potential difference of each grounding point and avoid mutual interference, the loop grounding system should use equipotential connection; The type grounding system adopts the radiation type grounding system inside the electronic equipment and the ring type grounding system outside the electronic equipment.
5. For the section of the grounding ring busbar, when the frequency of the electronic equipment is above 1mhz, use copper foil of 120mm × 0.35mm; when it is below 1mhz, use copper foil of mm × 0.35mm.
6. The grounding electrode of electronic equipment should be laid horizontally underground, in the shape of a rake or a star.
d. Grounding of data processing equipment
The grounding resistance of data processing equipment is generally 4ω. When used with AC power frequency grounding and lightning protection grounding, the grounding resistance is 1ω.
2. For data processing equipment with a leakage current of more than 10ma, the metal bodies in the host room should be connected to each other. The connecting wire can be made of 6mm2 copper wire or 25mm×4mm galvanized flat steel, and grounded, and the grounding resistance is not greater than 4ω .
3. In order to reduce the skin effect and channel impedance, the down-conductor of the DC working ground should be a multi-core copper wire, and the cross-section should not be less than 35 mm2. When the working conditions of the signal need to be improved, the multi-strand copper stranded wire should be used.
4. If the common grounding is not used for the DC working grounding and the AC working grounding, the electric difference between the two should not exceed 0.5v to avoid interference.
5. The cables of the input signal are laid through steel pipes, or are laid in metal bridges with metal cover plates. Both the steel pipes and the bridges should be grounded.
e: Grounding of electro-acoustic and TV systems
The grounding resistance of electroacoustic and TV systems is generally 4ω. When the capacity of industrial TV systems is less than or equal to 0.5kva, the grounding resistance may not be greater than 10ω. The metal base of the antenna erected on the top of the building must be connected with the lightning protection net on the top of the building to form a lightning protection system, which is grounded through at least two downconductors in different directions or the main steel bars in the building.
In order to avoid the interference of AC stray waves due to the ground potential difference, CCTV and industrial TV must be grounded at one point.
When the transmission cable of the TV system is laid through the metal pipe, the metal pipe should be grounded to prevent interference.
f: Installation of ground electrode and ground wire
When the strong and weak current adopts a joint grounding electrode, the grounding resistance must be less than 1ω.
2. When using a joint grounding electrode, the weak current grounding lead wire and the strong current grounding lead wire cannot be led out from the same point, and the distance between the two should be more than 3m.
3. For equipment with high anti-interference requirements, such as computers and fire control rooms, use two insulated copper conductors with a cross-sectional area of not less than 25 mm2 or a grounding bar fixed on an insulator to avoid being connected with the strong electric grounding line.
The above is the whole content of the grounding precautions for the weak current system. I believe that everyone here has a clear understanding of the grounding precautions for the weak current system. I hope to give you some help.
