You've described a common and generally sound grounding setup. Let's break down why connecting the MV switchgear enclosure to the main ground bar is generally recommended, even though technically it might seem redundant based on your explanation.Here's the reasoning: Redundancy and Safety

Your equipment grounding conductor coming in with the 3-phase feeder should ground the MV switchgear enclosure. However, relying on a single ground path for safety is risky. The EGC could be damaged, disconnected, or develop high impedance. A separate connection to the main ground bar provides a second, independent ground path. This significantly enhances safety, especially in fault conditions.

Voltage Gradients

During a ground fault in the MV switchgear (e.g., insulation failure), the ground potential rises locally. Without a connection to the main grounding electrode system, this potential difference between the switchgear enclosure and other grounded equipment in the building could be substantial. This creates a shock hazard. Connecting to the main ground bar minimizes these potential differences, improving personnel safety.

Shielding and Noise Reduction

A good grounding system helps with electromagnetic interference (EMI) and radio frequency interference (RFI). Connecting the MV switchgear enclosure to the main ground bar can improve shielding and reduce noise in sensitive electronic equipment.

Code Compliance

While the NEC (National Electrical Code) requirements can be interpreted differently depending on the specific installation and local interpretations, it's generally considered best practice and often required to connect the enclosures of electrical equipment, including switchgear, to the grounding electrode system. This is not only for fault current carrying but also to equalize ground potential and minimize touch potential hazards. Your local inspector will have the final say.

Minimizing circulating currents By connecting both MV and LV gear to a common ground bar, it can minimize the potential for creating circulating ground currents between the two.

Specific Recommendations & Considerations


Direct Connection

The most effective way to ground the MV switchgear is with a dedicated, low-impedance conductor (typically copper) directly from the switchgear enclosure to the main ground bar in your electrical room. Size this conductor according to code and engineering best practices.2.

Consider a Grounding Bus Inside MV Gear

You may have a grounding bus or pad already built into the MV switchgear enclosure. If so, use that as your connection point.3.

Bonding Jumpers

Ensure all sections of the MV switchgear enclosure are properly bonded together internally (if they are separate compartments bolted together). Verify the integrity of these bonding connections.4.

Utility Requirements

Consult with your utility company's requirements. They may have specific grounding standards that you must follow, particularly for MV equipment.5.

Engineering Study

For complex installations, a ground grid analysis or grounding study by a qualified electrical engineer is highly recommended. This helps optimize the grounding system design for safety and performance.

In summary:

While your existing grounding arrangement might* be compliant based on the incoming EGC, adding a separate connection from the MV switchgear enclosure to the main ground bar provides significant benefits in terms of safety, reliability, and potential code compliance. It's considered a best practice and is highly recommended. Consult with a qualified electrical engineer to review your specific installation and ensure it meets all applicable codes and standards. Flag for review