A good grounding system is required to ensure the safety of using AC and DC electricity. Below, the editor in charge of graphite grounding will introduce how to ground a closed-circuit monitoring system.

DC grounding

DC working ground is the common reference zero potential of all logic circuits in a computer system, which is the logic ground. Logic circuits generally operate at low levels, with small signal amplitudes, and are susceptible to interference from ground potential differences and external magnetic fields. Therefore, a good DC working ground is required to eliminate the effects of ground potential differences and magnetic fields.

There are usually three types of grounding methods for direct work in computer rooms: series connection method, collection method, and grid method.

Serial method

The series connection method is to lay a bronze (or purple copper) strip with a cross-sectional area of (0.4-1.5mm) × (5-10mm) under the floor. Each device should connect its DC ground to the nearby copper belt under the floor. The advantage of this connection is that it is simple and easy to implement, but the disadvantage is that the current flow on the copper strip is single and the impedance is not small, resulting in some differences in potential at various points on the copper strip. This type of connection is generally used in smaller systems.

Collection method

The aggregation method is to set up a copper plate with a thickness of 5-20mm and a size of 500 × 500mm under the floor. Each device uses multiple shielded flexible wires to connect its DC ground to this copper plate. This connection method, also known as parallel connection, has the advantage that there is no potential difference between the DC and ground of each device, but the disadvantage is that the wiring is chaotic.

grid method

The grid method uses copper strips with a cross-sectional area of approximately 2.5mm × 50mm to lay grid grounding wires throughout the entire computer room. The grid mesh size is consistent with the size of the raised floor, and the intersection points are welded together. Each device should connect its DC ground to the nearest grid ground wire. The advantage of this method is that it has both the advantage of consistent logical potential reference points in the aggregation method and the advantage of simple series connection. Moreover, it greatly reduces the internal noise and external interference of the computer system; This method is suitable for large and medium-sized computer rooms with large computer systems and numerous network devices.

Communication grounding

A large number of devices are electrical equipment that use alternating current. These devices are required to be grounded during operation according to regulations, that is, the neutral wire in the three-phase four wire AC system is directly connected to the ground, which is called AC working grounding. The grounding of communication work usually adopts the method of connecting the neutral point to the earth and repeatedly connecting the neutral line to the earth. The so-called repeated connection to the earth refers to multiple connections to the earth through grounding devices at multiple locations on the neutral line.

After the neutral point is grounded, when one of the AC phase lines touches the ground, the grounding resistance of the neutral point is only a few ohms, so the grounding current becomes a large single-phase short-circuit current. At this time, the corresponding protective equipment can quickly cut off the power supply, thereby protecting the safety of personnel and equipment. The implementation of the communication work site is considered to be led directly from the grounding electrode to the MEB box in the substation room using 40 * 4 galvanized flat steel.

Safety protection grounding

Safety protection grounding is the process of directly connecting the metal casing or frame of electrical equipment to the ground through a grounding device. Its purpose is to prevent the risk of electric shock caused by insulation damage or other reasons that may cause the metal casing of the equipment to become electrified. After installing the safety protection grounding, due to the fact that the resistance of the safety protection grounding wire is much lower than that of the human body, the leakage of the equipment's metal shell or frame is directly introduced into the ground, and there is no risk of electric shock when the human body comes into contact with the live metal shell.

The power cord of the equipment adopts a single-phase three wire cable, with one wire as the live wire, one wire as the neutral wire, and one wire as the PE wire or three-phase five wire system. This PE line is connected to the metal casing in the equipment. A safety protection ground connection point should be set up to connect with the safety protection ground wire in the computer room. The power socket connected to the device should use a three hole socket and be uniformly connected to the contact of the safety protection ground. Thus establishing an effective safety protection grounding.

lightning protection grounding

The damage caused by lightning to equipment can be mainly divided into three categories. The first type is the damage caused by direct lightning strikes, that is, lightning strikes directly on buildings or equipment, causing them to heat up, burn, and mechanically split and destroy; The second type is the destruction caused by induced lightning, which is the second effect of lightning. The electromagnetic and electrostatic effects generated by the powerful lightning magnetic field cause induced voltages of up to hundreds of thousands of volts in metal components and electrical circuits, posing a threat to buildings, equipment, and even personal safety; The third type of damage is caused by lightning currents passing high volts of lightning voltage along electrical and pipeline lines to the interior of buildings and equipment, resulting in damage.

The national standard GB9361-88 stipulates the requirements for lightning protection measures in the "Code for Design of Lightning Protection of Buildings". There are generally two types of lightning protection design for buildings: one type of lightning protection building, with a lightning protection grounding resistance requirement of no more than 5 Ω; For Class II lightning protection buildings, the grounding resistance for lightning protection should not exceed 10 Ω. This project has three underground floors and fifty above ground floors, with a main height of 220 meters. It is a Class I super high-rise building, and lightning protection grounding should be designed according to the requirements of Class II lightning protection buildings. At the same time, in the event of lightning strikes, there will be a large current flowing into the ground through lightning protection grounding. The amplitude of the lightning current is generally several kA to several hundred kA, and the grounding electrode and the ground potential near it will generate an instantaneous high potential. If there are grounding electrodes of other grounding systems near the lightning protection grounding electrode, interference will occur. Therefore, lightning protection grounding should be strictly separated from other grounding and maintained at a certain distance. In areas with hot and humid climate and frequent thunderstorms, attention should be paid to increasing the distance between the two, generally greater than 20m. In areas with frequent lightning, surge voltage absorption devices should be installed.

Anti static grounding

The harm of static electricity to computer systems and equipment in computer rooms mainly manifests in: damage to instrument and equipment components; Generate errors in data transmitted by computers; Mechanical operation of computer peripherals causing misoperation. Grounding is the most basic anti-static measure in computer rooms. According to Article 6.3.5 of the national standard GB50174-93 "Design Specification for Electronic Computer Room", static electricity grounding must be carried out for conductive floors, raised floors, workbenches, and seat cushions. We should also connect the static conductive activity floor, aluminum alloy ceiling, composite aluminum wall, metal partition keel, and DC ground of the computer room to discharge the static electricity accumulated on these surfaces into the ground, in order to eliminate most of the static charges accumulated on the room walls, ceiling, and ground; By safely grounding the equipment, static charges accumulated on the metal surfaces of computer systems and other supporting devices can be eliminated. Meanwhile, when an electrostatically charged object touches the surface of a room or computer casing, static electricity can be introduced into the ground through the grounding system without affecting the computer equipment. So, electrostatic grounding is usually shared with equipment DC grounding and safety grounding, and the lower the grounding resistance, the better.

The above is an introduction to how to ground a closed-circuit monitoring system made by the editor of graphite grounding.