Grounding requirements for distribution box bolts

Distribution box bolts must provide a low-resistance, secure connection to the grounding system, typically using properly sized copper conductors, star washers, and clean metal contact surfaces.Bolt Connection and Material ConsiderationsMaterial Matching: Use connectors that match the enclosure material (e.g., stainless steel) to prevent galvanic corrosion .Surface Preparation: Remove coatings, paint, or oxide layers around bolt holes to ensure direct metal-to-metal contact . Star washers or serrated washers are recommended to maintain a reliable electrical connection .Torque and Thread Depth: Ensure bolts are tightened to manufacturer-specified torque values, and pre-drilled threads are deep enough to accommodate multiple wires if needed .Conductor Sizing and ConnectionGround Wire Size: For U.S. installations, a minimum of 10 AWG (5.26 mm²) copper wire is used; in other markets, 6 mm² is typical .Connection Path: Attach a ground wire from the threaded stud on the distribution box to a mounting plate, then from the mounting plate to the central grounding point . For multiple spindles or long tool cables, larger conductors (e.g., 16 mm² or 6 AWG) may be required to maintain low resistance .Bonding Jumpers: Use flexible copper braid or jumpers across moving parts, such as hinged doors, to maintain continuity .Resistance and TestingTarget Resistance: The total grounding resistance should be very low, typically