All distribution boxes must be grounded

Yes, all distribution boxes, especially metallic ones, must be grounded to ensure safety, equipment protection, and code compliance.

Mandatory Grounding

Grounding of distribution boxes is required for all metallic enclosures. According to NEC 314.28, metal boxes must be reliably grounded and bonded, and NEC 250.148 specifies that metallic junction boxes and cabinet doors must be connected to ground using a designated grounding screw or clip . Non-metallic boxes generally do not require grounding unless they contain metallic frames, hinges, or components that could become energized .

Purpose of Grounding

Proper grounding serves several critical functions:

• Safety of personnel: It channels fault currents safely into the earth, reducing the risk of electric shock .
• Equipment protection: Grounding protects electrical components from lightning strikes, transient overvoltages, and fault currents .
• System stability: A well-designed grounding system stabilizes voltage levels and ensures protective devices like circuit breakers operate correctly .
• Fault detection: Grounding provides a clear path for fault currents, allowing protective devices to isolate faults efficiently .

Proper Grounding Methods

For high and low voltage distribution boxes, grounding should include the following steps :

1. Connect the PE (protective earth) bus in the box directly to the main power ground or grounding system.
2. Ground the metal enclosure using a dedicated grounding bolt connected to the PE bus with a copper wire or braided conductor.
3. Bond metal conduits connected to the box to the enclosure to maintain continuity.
4. Ground internal components that require protection by connecting them to the PE bus.
5. Ensure low resistance: The total ground resistance between system parts should typically be below 0.1 ohm for industrial applications .

Additional Considerations

• Distribution box doors: Metal doors must be bonded to the cabinet using a dedicated grounding screw and wire .
• Wire sizing: Ground wires should meet local standards, e.g., 10 AWG in the US or 6 mm² elsewhere .
• Inspection and testing: Grounding connections should be tested to ensure continuity and low resistance, preventing potential hazards .

In summary, all metallic distribution boxes must be grounded, and proper grounding is essential for safety, equipment longevity, and compliance with electrical codes. Non-metallic boxes may not require grounding unless they include conductive parts.