Should round steel be used for grounding secondary distribution boxes

Round steel rods are generally not recommended as the primary grounding conductor for secondary distribution boxes; proper grounding requires materials and methods that ensure low-impedance, continuous paths in compliance with NEC standards.

Material Considerations

For grounding secondary distribution boxes, the National Electrical Code (NEC) specifies acceptable equipment grounding conductors, including rigid metal conduit (RMC), intermediate metal conduit (IMC), and electrical metallic tubing (EMT), which can serve as grounding paths when properly installed with tight joints. Round steel rods, such as plain steel grounding rods, are typically used as grounding electrodes rather than as conductors connecting the distribution box to the system ground. Using round steel as a conductor may not provide the necessary low-impedance path for fault currents unless it is copper-bonded or otherwise treated for conductivity and corrosion resistance.

Installation and Continuity

Grounding effectiveness depends on continuous, low-impedance connections. In metal boxes, grounding conductors can be attached with ground screws or clips, and if metal raceways like EMT are used, a separate wire-type conductor may not be required inside the box. Any break in the grounding path, loose joints, or corrosion can compromise safety, potentially allowing dangerous voltages to persist on metal parts.

Round steel rods alone, without proper bonding and connection to the box, may fail to meet these continuity requirements.

Recommended Practice

Use copper or copper-bonded steel rods as grounding electrodes driven into the earth, connected to the distribution box via a properly sized copper grounding conductor. Ensure metal raceways or conduits are bonded to the box to serve as effective grounding paths. Test the grounding system to maintain resistance below 25 ohms for safety and compliance.

Avoid using plain round steel rods as the sole conductor between the box and the grounding electrode, as they may corrode and increase impedance over time.

Conclusion

While round steel rods are suitable as grounding electrodes, they should not be used alone as the grounding conductor for secondary distribution boxes. Proper grounding requires continuous, low-impedance paths using approved conductors and bonding methods, typically involving copper or copper-bonded materials, metal conduits, and secure connections to the box in accordance with NEC Article 250. This ensures safe dissipation of fault currents and protection of equipment and personnel.