Grounding posts for distribution boxes must ensure low-resistance connections using appropriately sized conductors, secure mechanical attachment, and corrosion-resistant materials.

Grounding Wire and Resistance Requirements

For proper grounding, each distribution box must be connected to the factory or building ground using a dedicated conductor. In the US, a 10 AWG (5.26 mm²) ground wire is standard, while in other markets, a 6 mm² wire is recommended . The total grounding resistance between all system parts should be less than 0.1 ohm to ensure safety and effective fault current dissipation . For connections between mounting plates and spindle plates, larger wires such as 16 mm² (or 6 AWG in the US) may be used depending on cable length and number of spindles .

Grounding Post Material and Construction

• Material Consistency: The grounding post should match the enclosure material (e.g., stainless steel) to prevent electrochemical corrosion .
• Thread Depth and Strength: Pre-drilled threads must support the required tightening torque for multiple wire connections .
• Contact Surface: Remove coatings or oxide layers to expose bare metal, reducing contact resistance .
• Anti-Loosening Measures: Use washers or locking nuts to prevent loosening due to vibration or repeated door operation .
• Flexible Bonding: For moving parts like hinged doors, flexible copper braided tape is recommended to maintain stable contact .

Installation Practices

• Connection Points: Attach the ground wire from the threaded stud at the bottom of the housing to the mounting plate, then from the mounting plate to the central grounding point .
• Bonding: All metal parts, including doors, panels, and frames, should be bonded to the ground bus using short-circuiting cables or dedicated ground lugs .
• Cable Specifications: Short-circuiting cables connecting cabinets should have a cross-sectional area of at least 6 mm² and a maximum length of 300 mm .
• Corrosion Protection: Apply conductive paste or zinc electroplating with chromate conversion coating to prevent oxidation at contact points .

Compliance and Testing

• Resistance Testing: Verify that the grounding resistance meets design standards (e.g., <0.1 ohm for industrial distribution boxes, <1 ohm for communication buildings, <5 ohms for ordinary offices), .
• Insulation: Use separate insulated green ground conductors for each feeder and branch circuit, connecting them to the panel ground bus .
• Bonding Jumpers: Install jumpers across expansion or deflection fittings to maintain continuity .

By following these specifications, grounding posts in distribution boxes will provide reliable electrical safety, minimize contact resistance, and prevent corrosion, ensuring long-term performance in both indoor and outdoor environments.