Yes, distribution boxes in power distribution rooms must be grounded to ensure safety, equipment protection, and compliance with electrical standards.

Importance of Grounding

Grounding distribution boxes provides a low-resistance path for fault currents, which helps protect personnel from electric shock, prevents equipment damage from transient overvoltages or lightning, and stabilizes system voltage levels for reliable operation . Proper grounding also facilitates fault detection and isolation, allowing protective devices like circuit breakers to operate effectively .

Grounding Requirements

• Metal Enclosures: All metallic distribution boxes and their components, including doors, must be bonded to ground. This prevents the enclosure from becoming live if a fault occurs inside the box .
• Internal Components: Controllers, mounting plates, and other conductive parts inside the box must also be grounded to the central grounding point .
• Wire Sizing: In the US, a 10 AWG (5.26 mm²) ground wire is typically used, while other markets may require a 6 mm² wire . The total ground resistance between system parts should be less than 0.1 ohm to ensure effective fault current flow .

Grounding Methods

1. Bonding the Box: Attach a ground wire from a designated grounding stud on the box to the mounting plate, and then from the mounting plate to the central grounding point .
2. Door Grounding: Even if the box body is grounded, metal doors should have a dedicated grounding wire or clip to prevent static discharge and protect against accidental contact with live components .
3. Continuous Grounding System: All metallic enclosures, raceways, and equipment grounding conductors should be bonded into a continuous system to maintain equal potential and reduce step and touch hazards .

Regulatory References

• NEC 250.148: Requires metallic junction boxes and cabinet doors to be bonded to ground.
• NEC 314.28: Mandates reliable grounding of metal boxes.
• IEEE Recommendations: Suggest using equipment-grounding conductors sized equal to phase conductors for improved safety and power quality .

Summary

Grounding distribution boxes is mandatory for safety and compliance. Both the box body and any metal doors must be properly bonded to the grounding system, and internal conductive components should also be connected to the central ground. Using appropriately sized grounding conductors and maintaining low resistance ensures effective fault current management, personnel safety, and equipment protection .