Electrical equipment grounding common sense - Solutions - Huaqiang Electronic Network

Test - lowercase jpg

Kaixin micro test

Test probe P100-M3

A reliable electrical connection between a part of an electrical device and a large conductor, such as the earth, is known as grounding. This process involves metal conductors that are in direct contact with the ground and are referred to as joints. The connections between the equipment and these conductors are called wiring, and together, the joints and wiring form the overall grounding system. Grounding is essential for ensuring both personal safety and the protection of electrical equipment. All electrical devices must be properly grounded according to established standards and regulations. There are two main types of grounding: protective grounding and functional grounding. (1) Protective grounding is used to prevent electric shocks and ensure personal safety. It involves connecting the metal casing of electrical equipment to the grounding system. If a person comes into contact with a live casing, the current will preferentially flow through the low-resistance grounding path rather than through the human body, significantly reducing the risk of injury. (2) Functional grounding ensures the safe and stable operation of electrical systems under normal and fault conditions. Examples include neutral point grounding, repeated grounding of the neutral line, and lightning protection grounding. These types of connections help maintain system integrity during faults or abnormal situations. The total resistance of a grounding system includes several components: (1) Contact resistance between the equipment and the wiring. (2) Resistance of the wiring itself. (3) Resistance of the equipment's internal structure. (4) Contact resistance at the joint and the ground. (5) Resistance of the ground itself. Different applications have varying requirements for grounding resistance: (1) In high short-circuit current systems, the resistance should be ≤ 0.5 Ω. (2) For transformers or generators with a capacity above 100 kVA, the resistance should be ≤ 4 Ω. (3) For valve-type surge arresters, the resistance should be ≤ 5 Ω. (4) For low-voltage metal poles, concrete poles, and chimneys, the resistance should be ≤ 30 Ω. The exact values should be verified against technical specifications and local standards. Installation and maintenance requirements include: (1) Using galvanized flat steel of 40 mm × 4 mm for wiring. (2) Using galvanized steel pipes or angle iron for the grounding electrode. The pipe diameter should be 50 mm, with a wall thickness of at least 3.5 mm and a length of 2–3 meters. Angle iron should be 50 mm × 50 mm × 5 mm. (3) Placing the top of the grounding electrode 0.5–0.8 meters below the surface to avoid frozen soil layers. The number of electrodes depends on the soil resistivity, typically not less than two, spaced 3–5 meters apart. (4) Keeping a minimum distance of 1.5 meters from buildings and 3 meters from independent lightning rods. (5) Using lap welding for all connections between the wiring and the grounding electrode. To reduce soil resistivity, several methods can be applied: (1) Modifying the soil structure by mixing water, moisture-retaining materials like charcoal and slag into the surrounding soil within a 2–3 meter radius. This can improve conductivity. (2) Applying salt and charcoal in alternating layers. Charcoal is placed in layers about 10–15 cm thick, followed by 2–3 cm of salt, repeated 5–8 times. This method can reduce resistivity by up to 60–80%. (3) Using long-lasting chemical resistance reducers, which can lower soil resistivity by up to 40%. Regular testing of the grounding resistance is crucial. It should be tested once a year in spring and autumn using specialized instruments like the ZC-8 ohmmeter or the ammeter-voltmeter method. Additional checks should include: (1) Ensuring that all bolts are tight and free from rust. (2) Inspecting underground wiring and joints for corrosion or disconnection. (3) Checking the condition of exposed wiring for damage, breaks, or corrosion. Proper grounding is a critical aspect of electrical safety and system reliability, and it should be maintained carefully throughout the life of the installation.