Regulations on the Location of Grounding Bolts in Distribution Boxes

Grounding bolts in distribution boxes must be installed to ensure continuity of equipment grounding conductors, with metal boxes requiring a dedicated grounding screw and nonmetallic boxes requiring internal conductor connections.

General Requirements

According to the National Electrical Code (NEC) Article 250, all grounding and bonding work must provide a low-impedance path for ground-fault current and maintain continuity even if devices are removed from the box. Grounding bolts or screws are used to connect equipment grounding conductors to metal boxes, ensuring that the box itself is part of the grounding path.

Metal Boxes

Grounding bolts or screws must be installed in metal boxes to connect one or more equipment grounding conductors. The grounding screw must be used solely for grounding purposes and can be a listed grounding device or part of the equipment listed for grounding. Connections should maintain continuity so that removing a receptacle, luminaire, or other device does not interrupt the grounding path.

Direct metal-to-metal contact between device yokes and the box may sometimes eliminate the need for a separate bonding jumper, provided the connection is reliable.

Nonmetallic Boxes

Nonmetallic boxes cannot provide grounding continuity through the box itself. All equipment grounding conductors entering the box must be connected together inside the box using wire nuts or listed connectors, allowing any device in the box to be grounded. A grounding bolt is not attached to the box itself but may be used to facilitate connections to devices requiring grounding.

Placement Considerations

Grounding bolts should be located where they are accessible for inspection and testing. They must allow for proper connection of all conductors without creating strain or interference with other wiring. The arrangement should prevent hazardous differences in electric potential, as emphasized in OSHA protective grounding guidelines for distribution equipment.

Testing and Resistance

Proper grounding installations should be tested to ensure maximum resistance of 25 ohms or less, confirming effective dissipation of fault currents. Connections must be secure and corrosion-resistant to maintain long-term reliability.

Summary

In practice, metal distribution boxes require a dedicated grounding screw or listed device, while nonmetallic boxes require internal conductor connections. All grounding connections must maintain continuity, be accessible, and comply with NEC Article 250 and OSHA safety standards to ensure protection against electrical faults and hazards.