Electrical appliances in the bathroom may generate dangerous potentials, or may introduce dangerous potentials from other places. When bathing, the wet impedance of human skin decreases, and the safe voltage that human body can bear at this time is 12V. If this voltage is exceeded, people's heart will have ventricular fibrillation, blood circulation, especially the blood supply of the central nervous system, will not be maintained, and people will die of systemic hypoxia in a very short time, so the bathroom is a highly dangerous area. However, as long as there is no potential difference, there will be no current. For example, a bird standing on a single high-voltage line will not be shocked, which proves that as long as the object is in an area with equal local potentials, no matter how high the voltage in this area is, it is safe.
According to this principle, all conductive appliances in the bathroom are connected to the LEB junction box through equipotential bonding wires, so that they are at the same potential, which can prevent dangerous contact voltage.
2. The reason for the potential danger in the bathroom.
2. 1 A good conductor of electricity installed in the bathroom through metal pipes and metal objects, such as metal water supply riser, cast iron drainage pipe, gas pipe, solar hot water metal water supply pipe, metal bathtub, metal washbasin, etc. , will introduce dangerous potential factors in other places. For example, the pipeline extending out of the roof conducts lightning, and the dangerous potential of the upper and lower floors is conducted to the bathroom of this floor through the metal water supply riser.
2.2 Transmission through wires. (1) When the electrical equipment in the bathroom is short-circuited, the insulation is aging, the neutral point of the power line is offset, the leakage protector in the sub-box fails, and the PE line is disconnected, the equipment shell and the pipeline connected with the equipment may be charged, resulting in dangerous potential in the bathroom. At this time, the human body will get an electric shock when it touches a charged body. (2) If the bathroom is equipped with weak current lines such as telephone, cable TV, network and call button, its low voltage can also cause electric shock when taking a bath, and there may be dangerous potentials (such as lightning waves) invading the bathroom through these lines.
2.3 Lightning induces a dangerous potential. Generally speaking, the whole building has formed a faraday cage by welding lightning protection downlead, equalizing ring, foundation beam, pile foundation and other measures. Because of the shielding effect, there is no current in the bathroom in the building. The metal window of the bathroom outside the building is hit by lightning from the side, and the lightning current flowing through the down lead will induce voltage and current to the metal objects in the bathroom. For tall buildings, the down conductor is very long, the induced voltage drop of lightning current will be great, and there will be a counterattack phenomenon to conduct dangerous potential to the bathroom.
3. Misunderstanding of local equipotential in medical care.
(1) The electrical appliances in the bathroom have been grounded through the PE line. (2) On page 16 of Equipotential Connection Installation 02D50l-2, the LEB line is covered with BVR- 1× 4mm2 conductor on the ground or in the wall, but the PE line of some sockets in the bathroom is BV-2.5mm2, which violates the regulation that the PE branch line shall not be larger than the main line. (3) The concrete itself is not conductive, so there is no need to weld steel mesh in it. (4) As long as the bathroom floor steel mesh is welded through, it does not need to be welded into a grid of not more than 0.6m×0.6m (5) After the bathroom floor steel mesh is connected, it should be welded with the vertical main reinforcement in the nearby column, and then led to the total equipotential plate by the main reinforcement. (6) The ground steel mesh in the bathroom must be welded with the lightning protection downlead. (7) The grounding resistance should be tested for local equipotential. (8) The bathroom pipeline passes through the floor metal sleeve, and the pipeline metal bracket does not need equipotential connection. (9) The reinforcement of the bathroom floor should be welded with the foundation ground beam. (10) It is not necessary to weld round steel jumper wires on the surrounding ring beams. (1 1) The intersection of steel bars in the bathroom floor has been bound with iron wires to form equipotential, and welding is not needed. (12) There is no need for local equipotential connection for metal pipes with total equipotential. (13) The composite water supply pipe does not need equipotential connection. (14) The floor reinforcement must be welded with round steel, and the length must reach 6 times the diameter of the round steel. (15) grounding resistance tester and insulation resistance tester can be used. (16) Local equipotential bonding lines can be laid through steel pipes.
4. How to ask about local equipotential construction?
4. 1 With the main concrete construction.
Spot welding is carried out at the intersection of floor reinforcement, and the socket PE line is introduced into the bathroom from the household box. (1) After the gluten binding of the toilet floor in civil engineering specialty is completed, spot weld the steel bar intersection with gluten not greater than 0.6m×0.6m, and use 12mm round steel to bridge the surrounding ring beams, so that the toilet ring can be integrated. At the same time, the bracing reinforcement of ring beam reinforcement in grid figure 8 should also be connected with this loop by spot welding. If there is a concrete wall, the reinforcement in the wall should be spot-welded into a grid of not more than 0.6m×0.6m, and the grid reinforcement should also be spot-welded with the ring beam around the floor. If steel bars are connected by straight threaded sleeves, the joints must be bridged. At the same time, we should pay attention to the connection without welding errors. (2) 12mm round steel is welded from the ring beam at the bottom of LEB box, which is convenient for connection with LEB box. The LEB box is generally located at an elevation of 0.5m below the washbasin, because it is easy to maintain and will not affect the beautiful decoration. (3) From the reserved 12mm round steel in the loop to the place where local equipotential bonding is needed in the future (such as the location of various metal pipes in the bathroom, ceiling, floor-to-ceiling metal doors and windows, metal railings, etc.). ), including metal sleeve. In the drawing, the grounding of the bushing is connected to the terminal on the pipeline through the wire after welding the terminal. In fact, the floor reinforcement can be welded with the bushing to improve the impression. (4) The fine decoration project must embed PVC20 pipes according to the example on page 02d501-2 equipotential bonding installation 16.
4.2 During brick wall construction, 25mm×4mm flat steel and reserved 12mm round steel shall be welded to connect the LEB box with the terminal, and the toilet socket box shall be connected with the LEB box with a diameter of 20mm plastic pipe. For the fine decoration project, 86 junction boxes should be reserved at corresponding positions on the wall. For the rough decoration project, the bolts can be welded with the reserved 12mm round steel to lead out of the wall, and then the residents can connect the appliances themselves when decorating.
4.3 In the decoration stage, the terminal board (box) adopts local equipotential connection, and the metal objects in the bathroom include metal bathtub, sewer pipe, water supply pipe, hot water pipe and heating pipe. Connect the grounding pipe clamp and BV——4mm2 conductor to the terminal board of LEB box to realize equipotential. Note that it is not appropriate to lead the connecting wire directly from the wall, and it is not appropriate to directly replace the grounding pipe clamp with a laryngeal cuff. Instead, after the transfer of 86 boxes, use BV-4mm2 conductor and grounding pipe clamp to connect with the places that need to be connected.
The bathroom socket box adopts BV-4mm2 copper core wire, which is connected with the equipotential bonding terminal box through a plastic pipe with a diameter of 20mm. Connect the reserved connection points with metal objects with BVR lines. There is generally no need to add jumpers to the metal pipe joints in the bathroom. If poor conduction is found, jumper wires should be made. When the water pipe in the bathroom is plastic pipe or composite metal pipe, the equipotential jumper can be connected to the end faucet; When metal water pipes are used, jumpers are directly connected to the water pipes. If there is a water meter in the bathroom, it should be bridged. Connect the keel of the bathroom metal ceiling with the connecting bolt reserved on the wall with BVR line. Note that if the water supply pipe in the bathroom is a plastic water supply pipe such as PPR, but the sanitary ware is a metal product, it should also be equipotential connected.
4.4 Materials and methods. According to the requirements of atlas, the connection between connecting conductors in equipotential bonding can be welded, bolted or welded. The equipotential connection terminal board should be fixed with bolts for easy disassembly and regular inspection.
Equipotential bonding wires and equipotential bonding terminal plates shall be made of copper. Bolts, washers, nuts, etc. Equipotential bonding terminal board should be hot-dipped galvanized to prevent corrosion; The equipotential bonding line can be BVR line, and the wiring color should be uniform (i.e. yellow-green line). Connecting wires should be concealed in plastic pipes, and it is forbidden to lay them in metal pipes. The galvanized flat steel hoop used for pipe connection should be more than 4mm thick and should be closed. The contact surface between pipeline and flat steel shall be cleaned with paint, and the contact shall be close. When welding flat steel and round steel, attention should be paid to repainting antirust paint. When connected with chrome-plated copper pipes such as washbasin sewer pipes, stainless steel grounding pipe clamps can be used for equipotential connection.
5, the effectiveness of equipotential bonding inspection and test methods and test time.
(1) According to the relevant provisions of IEC6036-6-6 1 Part 6-6-6l of Building Electrical Devices: Initial Inspection, DC or AC power supply with no-load voltage of 4-24V should be used in the test, and the test current should not be less than 0.2A If the voltage is too low, the measured contact resistance will increase and the test result will be inaccurate. It is also required that the resistance between the equipotential bonding terminal board and the metal ends such as metal pipes within the equipotential bonding range should not exceed 3 Ω. At present, there are special equipotential bonding resistance measuring instruments on the market. (2) When there is no special local equipotential tester on site, it can be measured by voltammetry. The principle of measuring resistance by voltammetry is ohm's law of circuit R= pa. When measuring resistance by voltammetry, in order to reduce the measurement error, there are usually two circuit connection methods: ammeter external connection and ammeter internal connection. If the voltmeter has internal resistance Rv>& gt in Rx and the shunt effect of the voltmeter is small, the ammeter external connection method should be adopted (the measurement result R of this method is true). If the internal resistance of Rx> ammeter is RA and the partial pressure of ammeter is small, the ammeter internal connection method should be adopted (the measurement result of this method is Rrinse >; R is empty). In general, the internal resistance of DC ammeter is 50 ~ 200Ω, and the internal resistance of voltmeter is 5 ~ 20kΩ, so I recommend the external connection of ammeter. At the same time, it should be noted that the average value should be obtained as the measured resistance by changing the voltage value many times. The test time is usually conducted after all potential connections are completed. However, in the fine decoration project, if the local equipotential construction only adopts the method of welding the bottom plate reinforcement and reserving round steel to the connection point, it should be measured before the concrete is concealed. At this time, the resistance between the reserved round steel of LEB box and the reserved round steel of connection point can be measured, and concealment can be carried out only after the resistance meets the requirements. If this requirement cannot be met, it can be corrected by embedding PVC pipes, replacing PE lines and reconnecting.