Grounding and Bonding in Subway Stations: Best Practices

In subway station design, grounding and bonding aren’t just technical requirements—they’re the foundation of electrical safety and system integrity. With high passenger density, complex equipment, and confined underground environments, a single grounding oversight can have serious consequences. That’s why I treat grounding and bonding as a design discipline in its own right.

Why Grounding and Bonding Matter

• Safety First: Proper grounding ensures that fault currents are safely diverted to earth, protecting both people and equipment.

• System Stability: Bonding equalizes potential across metallic components, reducing the risk of arcing, electromagnetic interference, and equipment malfunction.

• Code Compliance: Standards like PEC, NFPA 70, and NFPA 130 mandate specific grounding practices for transit environments—especially in tunnels and stations.

Best Practices I Apply in Subway Projects

1. Equipotential Grounding Grids
   I design grounding grids beneath electrical rooms and platform areas using copper conductors in a mesh layout. This minimizes step and touch potentials during fault conditions.

2. Bonding of All Metallic Components
   Every metallic enclosure, conduit, cable tray, and equipment frame is bonded using appropriately sized jumpers. This creates a unified grounding system that prevents dangerous voltage differences.

3. Dedicated Grounding for Sensitive Systems
   For SCADA, fire alarm, and communication systems, I often use isolated or dedicated grounding paths to reduce electrical noise and ensure signal integrity.

4. Use of Exothermic Welding
   In underground environments, I prefer exothermic welds (like Cadweld) for permanent, corrosion-resistant connections between grounding conductors and rods.

5. Fire-Rated and Corrosion-Resistant Materials
   I specify fire-rated grounding conductors in tunnel sections and use tinned copper or stainless steel in areas prone to moisture and chemical exposure.

6. Grounding of Third Rail and Traction Systems
   In electrified rail systems, I ensure that the negative return path is properly grounded and bonded to prevent stray currents and protect against electrocution.

7. Regular Testing and Maintenance Provisions
   I include test wells and access points for periodic ground resistance testing. This ensures long-term reliability and compliance with maintenance protocols.

A Lesson from the Field

In one underground station retrofit, we discovered elevated touch voltages near a metallic handrail during a routine test. The issue? A missing bonding jumper between the handrail and the nearby cable tray. Once installed, the potential difference dropped to safe levels—a small fix with a big impact.

Final Thoughts

Grounding and bonding in subway stations isn’t just about meeting code—it’s about designing with intention. It’s about protecting lives, preserving equipment, and ensuring that every system—from lighting to life safety—operates without compromise. In the underground world, grounding is your invisible shield.