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Preparation for Electrical Engineers: equipotential bonding of buildings can not be ignored

[Abstract] the international community attaches great importance to the role of equipotential bonding, which is very necessary for power safety, lightning protection and the normal work and safe use of electronic information equipment. According to theoretical analysis, the smaller the action range of equipotential bonding is, the safer it is electrically

1. Grounding is a wide range of equipotential bonding

safety grounding is also an equipotential bonding, which is a wide range of equipotential bonding with the earth potential as the reference potential. In the general concept, grounding refers to grounding, and not grounding violates the basic requirements of electrical safety. This concept has limitations. Electric shock accidents and electrical fires rarely occur during the flight of the aircraft, but the aircraft is not grounded. The safety of electricity use in aircraft does not depend on grounding, but on equipotential bonding, which takes the fuselage potential as the reference potential in the aircraft. Due to the narrow scope of the aircraft, even in the event of an insulation damage accident, the potential difference is very small, so the electrical safety of the aircraft is guaranteed, but due to the advanced structural design and high-level manufacturing industrial efficiency. People live on the earth, so they often need to be equipotential with the earth, that is, the electrical system and electrical equipment shell are connected with the earth, which is often referred to as grounding. The aircraft can be connected with the fuselage with terminal blocks, while the earth needs to be connected with the grounding electrode as the terminal blocks

2. Equipotential bonding installation of buildings

the national building standard design atlas "equipotential bonding installation" (97sd567) introduces the specific methods of equipotential bonding of buildings in detail. The scope of application of this atlas is: general installation drawings for equipotential bonding of electrical devices in general industrial and civil buildings to prevent indirect contact electric shock and explosion and fire caused by grounding fault. Lightning protection of buildings and protection of electronic information equipment from transient overvoltage and interference and other equipotential bonding installations should also be constructed in accordance with their corresponding requirements

2.1 classification of equipotential bonding and its conductive part

(1) total equipotential bonding (MEB)

the function of total equipotential bonding is to reduce the indirect contact voltage in the building and the potential difference between different metal parts, and eliminate the harm of dangerous fault voltage introduced from outside the building through electrical lines and various metal pipelines, It shall connect the following conductive parts with each other through the main equipotential bonding terminal board (grounding busbar) near the incoming distribution box; PE (pen) busbar of incoming distribution box; Metal pipes of public facilities, such as pipes for water, heat, gas, etc; If possible, it should include the metal structure of the building; If manual grounding is done, it also includes its grounding electrode lead

each incoming power line of the building shall be connected by general equipotential bonding, and each general equipotential bonding terminal board shall be connected with each other

(2) auxiliary equipotential bonding (SEB)

connect the two conductive parts directly with wires to make the fault contact voltage fall below the contact voltage limit, which is called auxiliary equipotential bonding

auxiliary equipotential bonding is required in the following cases: when the power network impedance is too large, so that the automatic power cut-off time is too long, and the requirements for preventing electric shock cannot be met; Fixed and mobile electrical equipment are supplied from the same distribution box of TN system, and the fixed equipment protection appliance can't meet the requirements of mobile equipment for preventing electric shock according to the difference of measurement method and the disconnection time of "strain gage extensometer", "camera extensometer", etc; In order to meet the special requirements of bathrooms, swimming pools, hospital operating rooms and other places for the prevention of electric shock

(3) local equipotential bonding (LEB)

when multiple auxiliary equipotential bonding needs to be made within a local site, the following parts can be connected with each other through the local equipotential bonding terminal board, so as to simply realize the multiple waste plastic composites within the local scope. It is a rich ore auxiliary equipotential bonding that needs to be developed urgently, which is called local equipotential bonding: PE bus or PE trunk line; Metal pipes of public facilities; If possible, including the metal structure of the building

2.2 selection of equipotential bonding wire and equipotential bonding terminal board

copper material should be used for equipotential bonding wire and equipotential bonding terminal board

(1) see Table 1 for the cross section of equipotential bonding wire

(2) the cross section of the equipotential bonding terminal board shall not be less than that of the connected equipotential bonding wire

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