Grounding pin model for secondary distribution box

Secondary distribution boxes should be grounded using a dedicated grounding busbar connected to the main grounding network, with all equipment and metal parts bonded to ensure an equipotential system.

Grounding Requirements

Secondary distribution boxes require proper grounding to protect equipment and personnel from electrical faults, overvoltages, and lightning disturbances. The grounding system establishes an equipotential network that connects all metal parts and devices to the main grounding grid, ensuring safe dissipation of fault currents and minimizing touch and step potentials .

Key Components

• Grounding Busbar: A copper busbar with a cross-sectional area of at least 100 mm² should be installed at the bottom of the distribution box or relay panel. This busbar serves as the central grounding point for all devices mounted on the panel .
• Device Connections: Each device's grounding terminal should be connected to the busbar using multi-strand copper wire with a minimum cross-sectional area of 4 mm² .
• Connection to Main Ground: The busbar must be connected to the main equipotential grounding network using a copper cable of at least 50 mm². In larger installations, multiple copper bars or cables may be used in parallel to maintain low resistance and reliability .
• Ground Rods: For outdoor or consumer-level distribution boxes, copper weld steel ground rods (16 mm diameter, 1x2400 mm long or 2x1200 mm) are recommended, with bare copper conductors of 35–70 mm² depending on voltage level .

Installation Guidelines

• Threaded Studs: Ground wires are typically attached to threaded studs at the bottom of the housing, which are then connected to the mounting plate and finally to the central grounding point .
• Wire Sizing: In the US, a 10 AWG (5.26 mm²) ground wire is standard, while in other markets a 6 mm² wire is used. For longer tool cables or multiple spindles, larger wires (up to 16 mm² or 6 AWG) may be required to maintain total ground resistance below 0.1 Ohm .
• Parallel Connections: When multiple grounding paths exist, the total resistance is calculated in parallel to ensure the overall resistance remains within safe limits .
• Equipotential Mesh: In control rooms or protection panels, a grid or mesh pattern of copper bars or cables ensures all points are at the same potential, reducing the risk of voltage differences that could damage sensitive equipment .

Safety Considerations

• Ensure no discontinuity exists between any load points and the grounding busbar.
• The neutral wire must only be connected to ground at a single point (typically at the service entrance or transformer neutral) to prevent circulating currents .
• All accessible metal parts of the distribution box and connected equipment must be bonded to the grounding system . By following these guidelines, the secondary distribution box will maintain a low-resistance, reliable grounding system, ensuring both personnel safety and stable operation of electrical equipment.