The metal casing of a distribution box must be grounded using a properly sized copper wire connected to designated studs and the main grounding system to ensure safety and low resistance.

Grounding Requirements

Each distribution box and controller must be grounded. In the US, a 10 AWG (5.26 mm²) copper wire is typically used, while in other markets a 6 mm² wire is standard . The grounding system should maintain a resistance of less than 0.1 Ohm between all connected parts .

Connection Points

1. Threaded Studs on the Housing: Attach a ground wire from one of the factory-installed threaded studs at the bottom of the metal enclosure to the mounting plate .
2. Mounting Plate to Central Ground: Connect a second wire from the mounting plate to the factory central grounding point or main electrical panel ground bus .
3. PE Bus Connection: Inside the box, the metal casing and all components requiring grounding should be connected to the PE (Protective Earth) bus using copper core wires or flexible braided wires .
4. Flexible Connections for Moving Parts: For doors or hinged panels, use flexible copper braided tape to maintain low-resistance contact despite movement .

Installation Considerations

• Wire Material: Use copper to prevent corrosion and ensure conductivity .
• Contact Surface: Remove coatings or oxide layers at connection points to reduce resistance .
• Mechanical Stability: Use anti-loosening washers and ensure proper torque on threaded studs to prevent loosening over time .
• Bonding: All metal parts, including threaded conduits or pipes connected to the box, should be electrically bonded to the casing .

Practical Tips

• Test the grounding resistance after installation to ensure it meets the <0.1 Ohm requirement .
• For long tool cables or multiple spindles, consider additional grounding wires between mounting plates and equipment to maintain low resistance .
• Ensure all connections comply with local electrical codes and standards, such as NEC guidelines in the US . Proper grounding of a distribution box casing is critical for electrical safety, preventing shock hazards, and ensuring reliable operation of connected equipment.