The outer casing of the distribution box must be grounded separately

Yes, the outer casing of a distribution box must be grounded, typically through a dedicated grounding connection to ensure safety and system stability.

Grounding Requirements

The metal casing of a distribution box is considered a conductive part that can carry fault currents. To protect personnel and equipment, it must be connected to the grounding system. This is usually done by attaching a ground wire from a threaded stud or dedicated grounding point on the housing to the mounting plate, which is then connected to the central grounding point of the facility . This ensures that any leakage or fault current is safely directed to earth.

Conductor Specifications

• In the US market, a 10 AWG (5.26 mm²) ground wire is commonly used.
• In other international markets, a 6 mm² wire is standard .
• The total ground resistance between all system parts should be less than 0.1 Ohm to maintain effective fault current dissipation .

Integration with System Ground

The outer casing grounding is not optional and is part of the overall protective grounding system. It may be connected in parallel with other grounding paths, such as the mounting plate to internal equipment, to ensure low-resistance paths for fault currents . Proper grounding stabilizes voltage levels, protects against surges, and facilitates fault detection .

Safety Considerations

• All metal parts inside the distribution box, including the installation board and appliance casings, should also be grounded.
• A leakage protector or residual current device is recommended for additional safety .
• Grounding must be performed by a qualified electrician to comply with local electrical codes and standards . In summary, the outer casing of a distribution box is separately grounded through a dedicated conductor to the facility's central grounding system, ensuring both personnel safety and equipment protection.