When installing the distribution box cabinet, how to ensure reliable grounding of the cabinet?
Publish Time: 2025-03-31
In the low-voltage power distribution system, reliable grounding of the distribution box is a key measure to ensure electrical safety, prevent electric shock accidents and reduce electromagnetic interference. If the grounding is poor, it may cause the equipment casing to be energized, the protection device to malfunction or refuse to operate, and even cause fire or casualties. Therefore, when installing the distribution box, the grounding construction must be carried out in strict accordance with the specifications to ensure the low impedance and long-term stability of the grounding system.
The reliability of the grounding system depends first on the selection of the grounding conductor. The grounding busbar of the distribution box is usually made of copper busbar or galvanized flat steel, and its cross-sectional area must meet the short-circuit current carrying requirements of the system. According to standards such as IEC 60364 and GB 7251, the minimum cross-sectional area of the main grounding conductor should generally not be less than 50% of the cross-sectional area of the phase line, and the cross-sectional area of the copper busbar is usually not less than 25mm² to ensure sufficient conductivity. For high-current systems, thermal stability and mechanical strength must also be considered to avoid melting or deformation of the grounding conductor due to short-circuit current shock. At the same time, the connection between the grounding conductor and the cabinet must be reliably fastened, such as galvanized bolts or welding, to ensure that the contact resistance is lower than the specified value (usually ≤0.1Ω).
The construction quality of the grounding grid directly affects the grounding effect of the entire system. The grounding of the distribution box should be connected to the main grounding device of the building, such as a foundation grounding electrode or an artificial grounding electrode. If an independent grounding electrode is used, it is usually necessary to use a galvanized angle steel or steel pipe to be driven vertically into the ground to a depth of not less than 2.5 meters, and multiple grounding electrodes are connected in parallel to reduce the grounding resistance. In areas with high soil resistivity, resistance reducing agents can be added or deep well grounding can be used to improve the grounding performance. The grounding resistance should be measured using a special grounding resistance tester (such as a megohmmeter or a digital grounding resistance meter), and its value is generally required to be ≤4Ω (for TN systems), and may be lower in lightning protection systems (such as ≤1Ω). If the test results do not meet the standards, it is necessary to check the buried depth of the grounding electrode and whether the conductor connection point is corroded or loose, and take corresponding corrective measures.
The grounding continuity inside the distribution box is also critical. All non-live metal parts such as metal casings, door panels, mounting brackets, etc. must be connected to the main grounding busbar through grounding wires to form a complete equipotential connection. For drawer-type distribution boxes, it is also necessary to ensure that the grounding contacts of the drawer units are in reliable contact when they are pushed in to avoid grounding failure due to vibration or oxidation. The shielding layer of the cables in the cabinet should also be grounded at one end to prevent circulation interference. In humid or corrosive environments, anti-corrosion measures (such as applying conductive paste or stainless steel fasteners) must be taken at the grounding connection points, and regular inspections must be carried out to avoid poor contact caused by rust.
Acceptance and maintenance after construction are key links to ensure long-term reliability of grounding. Before the distribution box is put into operation, a grounding continuity test must be carried out, and a low-resistance ohmmeter must be used to verify whether the resistance of each part of the cabinet and the grounding busbar meets the requirements. After commissioning, the grounding connection points should be regularly inspected for looseness and corrosion, especially during thunderstorm seasons or after earthquakes. For intelligent distribution boxes, the grounding status can also be monitored in real time through online monitoring devices to detect abnormalities in a timely manner.
In short, reliable grounding of distribution boxes is a systematic project, involving multiple links such as material selection, construction technology, test acceptance, and operation and maintenance management. Only by strictly following standard specifications can personal safety and stable operation of equipment be effectively guaranteed. As electrical systems develop towards intelligence, grounding technology also needs to be continuously innovated to meet higher standards of reliability requirements.
