The hottest residential electrical safety I

Residential electrical safety (I)

Abstract: This paper discusses the hierarchical division of equipotential bonding and the far-reaching significance of its implementation, and expounds the selection of equipotential bonding materials, construction technology and testing methods

key words: equipotential bonding material testing Untitled Document equipotential bonding, as the name suggests, is "an electrical connection that makes the potential of each external leakage conductive part basically equal to that of the conductive part outside the device". Generally, equipotential bonding is divided into three levels, namely, Mai equipotential bonding, local equipotential bonding and supplementary equipotential bonding, which is the latest concept of IEC and is also for good operation in practical work. Different levels have different connection conductor areas. General equipotential bonding refers to the connection of each power incoming line in the building and the metal pipes and metal structural members in and out of the building. Generally, there is a general equipotential bonding terminal board, which is radially connected or linked by the equipotential bonding terminal board. Auxiliary equipotential bonding generally refers to the auxiliary equipotential bonding when the grounding fault protection of a part of the electrical device cannot meet the time requirements for cutting off the circuit. After connecting the two conductive parts, the contact voltage can be reduced, Meet R ≤ 50/ia (R - between the exposed conductive part that can be touched at the same time and the conductive part outside the device, the voltage drop caused by the fault current causes the resistance of a segment of the contact voltage, in ohms, IA - the action current a of the protective appliance that cuts off the fault circuit for no more than 5S). After the connection between the two conductive parts, as long as the above formula can be met. Local equipotential bonding is generally in special dangerous places such as bathrooms, swimming pools, hospital operating rooms, etc. the risk of electrical accidents is relatively high, and lower contact voltage is required. In these local areas, multiple auxiliary equipotential bonding can meet the requirements. This connection is called local equipotential bonding. Generally, local equipotential bonding also has a terminal board or forms a ring. In short, local equipotential bonding can be regarded as the total equipotential bonding in the local range

now the international community attaches great importance to the role of equipotential bonding, which is very necessary for the safety of electricity gb1499.2 ⑵ 007 (steel for reinforced concrete Part 2: hot rolled ribbed steel), lightning protection, and the normal work and safe use of electronic information equipment. The familiar safety grounding is also equipotential bonding, but it is a wide range of equipotential bonding with the earth potential as the reference potential. According to theoretical analysis, the smaller the action range of equipotential bonding is, the safer it is electrically. If equipotential bonding is made within the scope of a residential building, the effect is of course much better than grounding. The so-called total equipotential bonding means that a copper grounding busbar is set near the power incoming distribution box in the residential building, and the following conductive metal parts are connected with the grounding busbar by equipotential bonding wire, as shown in Figure 1. When there is an artificial grounding electrode in the residential building, the grounding electrode lead-in wire should first be connected to the grounding busbar

according to the statistics of electrical accidents at home and abroad, the short circuit of low-voltage system is mostly the grounding fault (grounding short circuit) that the phase line touches the equipment shell, metal pipeline structure and the earth. It can make these equipment shells, pipelines and structures bring the ground fault voltage to cause personal electric shock or electrical fire accidents. The total equipotential bonding in the house can eliminate or reduce this fault voltage, and its effect is better than simple grounding. Therefore, the international electrical standard iec60364-4-41, the electrical standards of developed countries and China's electrical standards all stipulate it as the basic requirements of electrical safety

the bathroom is listed as a special place with high risk of electric shock by International Electrotechnical standards. Electric shock accidents also occur frequently in bathrooms in China. This is because people are soaked all over when bathing, and the human impedance is greatly reduced. One or twenty volts of voltage introduced into the bathroom along the metal pipe is enough to cause ventricular fibrillation and death. Therefore, an equipotential bonding should be made in the bathroom according to the above requirements. Due to the equipotential effect in such a small range, the potential difference in case of failure is negligible, which effectively ensures personal safety

in order to ensure the reliable conduction of equipotential bonding, the equipotential bonding wire and grounding busbar should adopt copper wire and copper plate respectively. Equipotential bonding, an electrical safety measure, does not require complex and expensive electrical equipment. It consumes only some conductors. It is not as vulnerable to soil corrosion and failure as the artificial grounding buried underground (in fact, it also realizes grounding when implementing equipotential bonding, because the water pipes and foundation reinforcement connected to it have played the role of low resistance and long life grounding), Its role in ensuring electrical safety is far better than the artificial grounding that we used to use in the past. In developed countries, households are not required to enter the artificial grounding, but if the general equipotential bonding and local equipotential bonding in the bathroom are not made in the residential building, the local power supply company also refuses to supply power on the grounds of electrical insecurity, thereby reducing the production cost of the enterprise

2 materials for equipotential bonding

copper materials are recommended for equipotential bonding wires and terminal boards because of their good conductivity and strength. However, when using copper materials to connect with foundation reinforcement or underground steel pipes, full attention should be paid to that copper and iron have different potentials. Due to the formation of electrolyte due to water and salts in the soil, galvanic batteries are formed, resulting in electrochemical corrosion, and the foundation reinforcement and steel pipes will be corroded, Therefore, in the soil, copper wire or steel wire with copper skin should be avoided as the connecting wire. If copper wire is used as the connecting wire, the discharge gap should also be used to connect with the pipe steel container or foundation reinforcement. When connecting with the foundation reinforcement, it is recommended to select steel for the connecting line, which is also best protected by concrete. The connecting part should be welded, and the particularity of the product should be properly adjusted at the same time of welding. The connecting part should be protected against corrosion accordingly, so that it is consistent with the potential basis of the foundation reinforcement and will not form electrochemical corrosion. When connecting with steel pipes in the soil, anti-corrosion measures should also be taken, If the cause of fatigue failure cannot be found out, wrap wires or cables with plastic wires or lead

3 equipotential bonding of microelectronic equipment

equipotential bonding of microelectronic equipment is of great importance in modern housing. Some data define it as the category of auxiliary equipotential bonding, and some define it as the category of local equipotential bonding. In a word, the equipotential bonding of microelectronic equipment has its particularity, which is different from the equipotential bonding of other electrical equipment. The equipotential bonding wire must be connected with the equipotential terminal board through the overvoltage protector, and cannot be directly connected with the equipotential terminal board. Its connection mode is shown in Figure 2