Electrical equipment grounding common sense - Solutions - Huaqiang Electronic Network

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A reliable electrical connection between a part of an electrical device and a large conductor is known as grounding. This connection ensures safety by providing a low-resistance path for fault currents to flow into the earth. Grounding is essential in electrical systems to protect both people and equipment from electric shocks and damage caused by overvoltage or short circuits.

There are two main types of grounding: protective grounding and working grounding. Protective grounding is used to safeguard individuals from electric shock by connecting the metal casing of electrical devices to the ground. If a fault occurs, the current will flow through the grounding system instead of through a person, significantly reducing the risk of injury. Working grounding, on the other hand, ensures the proper functioning of electrical equipment under normal and abnormal conditions. Examples include neutral point grounding, repeated grounding of the neutral line, and lightning protection grounding.

The total resistance in a grounding system consists of several components, including the contact resistance between the equipment and the wiring, the resistance of the wiring itself, the resistance of the grounding body, the contact resistance between the grounding body and the earth, and the resistivity of the soil. Different applications have specific requirements for grounding resistance:

• For systems with high short-circuit currents, the resistance should be less than 0.5 Ω.
• For transformers or generators with a capacity above 100kVA, the resistance should be less than 4 Ω.
• For valve-type surge arresters, the resistance should not exceed 5 Ω.
• For low-voltage metal poles, concrete poles, and chimneys, the resistance should be less than 30 Ω.

Proper installation is crucial for effective grounding. Typically, 40mm × 4mm galvanized flat steel is used for the wiring. The grounding electrodes can be made of galvanized steel pipes or angle iron. Steel pipes should have a diameter of at least 50mm, a wall thickness of no less than 3.5mm, and a length of 2–3 meters. Angle iron is usually 50mm × 50mm × 5mm. The depth of the electrode should be 0.5–0.8m to avoid frozen soil layers. Multiple electrodes (at least two) should be spaced 3–5 meters apart depending on soil resistivity.

The distance between the grounding system and buildings should be more than 1.5m, and the distance from independent lightning rods should be more than 3m. All connections must be made using lap welding to ensure a secure and durable bond. To reduce soil resistivity, methods such as soil replacement, adding salt and charcoal, or using chemical resistivity reducers can be applied. These techniques help improve the performance of the grounding system, especially in areas with high soil resistivity.

Regular testing of the grounding resistance is essential. It should be checked once a year during spring and autumn using specialized instruments like the ZC-8 megohmmeter or the ammeter-voltmeter method. Additionally, visual inspections should be conducted to check for loose bolts, corrosion, or damage to the wiring and connections. Ensuring the integrity of the grounding system is vital for maintaining safe and reliable electrical operations.