Basis for repeated grounding of terminal distribution boxes

Repeated grounding ensures safety, system stability, and proper fault current management by connecting the distribution box and neutral lines to multiple ground points.

Purpose of Repeated Grounding

Repeated grounding is implemented to enhance personnel safety, protect equipment, and stabilize the electrical system. By connecting the neutral point and the distribution box enclosure to multiple ground points, fault currents are safely channeled into the earth, reducing the risk of electric shock and preventing damage from transient overvoltages or lightning strikes. It also ensures that protective devices like circuit breakers operate correctly during faults.

Implementation Guidelines

Neutral Line Grounding: In a low-voltage three-phase four-wire system with a directly grounded neutral, the neutral main line should be grounded at multiple points along its length. For distribution lines exceeding 50 meters, the neutral line connected to the user should also be grounded repeatedly, with a grounding resistance not exceeding 10 ohms. Distribution Box Enclosure: The metal enclosure of the distribution box should be connected to the grounding grid using galvanized steel or flat steel, driven at least 2 meters into the ground.

All metal parts inside the box, including mounting boards and doors, should be bonded to the protective earth (PE) to ensure continuity. Grounding Grid and Conductors: A centralized buried grounding body is recommended for cable overhead lines, while indoor installations should use a ring or network-shaped grounding system. Protective neutral lines and repeated grounding devices should be connected at least at two points, including the farthest corner from the power supply line.

Resistance and Material Considerations: Grounding resistance should be kept low, ideally below 0. 1 ohm for industrial distribution boxes, using copper or galvanized steel conductors. Joints should be treated for corrosion protection to maintain long-term reliability.

Benefits

Safety: Reduces touch and step potentials, minimizing the risk of electric shock. Equipment Protection: Prevents damage from fault currents, surges, and lightning. System Stability: Maintains voltage levels and ensures proper operation of protective devices.

Fault Detection: Provides a clear path for fault currents, enabling rapid isolation of faults. Proper repeated grounding is a critical aspect of electrical distribution design, ensuring both operational reliability and safety for personnel and equipment.