All metallic parts of distribution boxes, including doors, must be properly grounded and bonded to ensure safety and compliance with electrical codes.

Key Regulatory Requirements

NEC Standards: According to NEC 250.148, all metallic junction boxes and cabinet doors must be bonded to ground using a dedicated grounding screw or clip, ensuring that every metallic component is electrically continuous . NEC 314.28 requires metal boxes to be reliably grounded, while NEC 110.26 ensures safe access to equipment doors without obstruction . NEC 250.122 specifies minimum sizes for equipment grounding conductors, though using a full-size conductor is recommended for improved safety and power quality . OSHA Guidelines: OSHA 1926.962 mandates protective grounding of transmission and distribution equipment to protect employees. Temporary protective grounds must prevent hazardous differences in electric potential, and grounding is required whenever equipment is de-energized for work . OESC Requirements: In Ontario, grounding connections for service boxes must be made at a single point, typically at the meter base, to prevent objectionable currents and ensure proper bonding between service boxes .

Practical Grounding Methods

Metallic Doors and Enclosures: For stainless steel or aluminum distribution boxes, bonding the door to the cabinet frame is essential. Flexible copper braided tape is commonly used to maintain low-resistance contact despite door movement . Pre-reserved points on the door and frame should be used, with anti-loosening washers to prevent loosening from repeated opening . Conductive paste can be applied to reduce oxidation and maintain reliable contact in high-humidity or outdoor environments . Equipment Grounding Conductors: All metal enclosures, raceways, and boxes should be bonded into a continuous grounding system. Using equipment grounding conductors sized equal to the phase conductors improves fault clearing times and overall safety . Connections should be tight, corrosion-free, and made with compatible materials to prevent electrochemical degradation . Outdoor and High-Humidity Considerations: Stainless steel enclosures may still experience oxidation at contact points. Proper surface preparation, conductive paste, and secure bonding help maintain low-resistance grounding and reduce the risk of localized overheating .

Summary of Best Practices

1. Bond all metallic parts, including doors, hinges, and frames, to the grounding system.
2. Use dedicated grounding screws or clips rather than relying on mounting bolts.
3. Ensure conductor sizing meets or exceeds NEC 250.122 recommendations.
4. Maintain low-resistance connections using flexible copper braids, anti-loosening washers, and conductive paste where necessary.
5. Follow single-point grounding for service boxes to prevent circulating currents.
6. Regularly inspect and maintain grounding connections, especially in outdoor or corrosive environments. Proper grounding of distribution boxes is critical for employee safety, equipment protection, and code compliance, ensuring that fault currents are safely diverted and voltage differences between metallic components are minimized .