Angle steel in a distribution box must be securely bonded to the grounding system using appropriately sized conductors to ensure a low-resistance path and electrical safety.

Purpose of Grounding

Grounding metal components like angle steel in a distribution box provides a low-resistance path for fault currents, preventing the metal from becoming energized and reducing the risk of electric shock or fire. It ensures that any stray current is safely diverted to the main grounding system, allowing protective devices like circuit breakers to operate effectively .

Connection Method

1. Identify Grounding Points: Use the designated threaded studs or mounting plates in the distribution box as connection points for grounding wires .
2. Select Proper Conductors: In the US, a 10 AWG (5.26 mm²) ground wire is standard, while in other markets, a 6 mm² wire is recommended . For connections between the mounting plate and angle steel, larger conductors (e.g., 16 mm² or 6 AWG) may be required depending on cable length and number of spindles to maintain low resistance.
3. Secure the Connection: Attach the grounding wire to the angle steel using a green hexagonal grounding screw, grounding lug, or clip. Ensure the screw bites into bare metal, removing any paint or coating to achieve a solid electrical bond .
4. Bond to Main Ground: Connect a second grounding wire from the mounting plate to the central grounding point of the facility. This ensures continuity and compliance with grounding standards .

Resistance Requirements

The total resistance between all grounded components, including the angle steel, mounting plate, and distribution box, should be less than 0.1 ohm. For longer tool cables or multiple spindles, calculate the parallel resistance of the tool cable and grounding wire to ensure the total resistance remains within safe limits .

Best Practices

• Always use copper conductors for reliable conductivity.
• Ensure mechanical stability of the connection to prevent loosening over time.
• Test the grounding system with an ohmmeter to verify resistance compliance.
• Follow local electrical codes such as NEC (NFPA 70) or equivalent regional standards . By following these steps, the angle steel in your distribution box will be properly grounded, ensuring both personnel safety and system reliability.