An earth mat (or grounding grid) is a high-conductivity network of interconnected horizontal and vertical electrodes buried in the soil to provide a low-resistance path for fault currents. By spreading electrical energy over a wide surface area, it effectively controls step and touch voltages, ensuring that high-voltage surges from lightning or equipment failure do not pose a lethal risk to personnel or delicate machinery
Earth mats are the foundational safety component for high-stakes electrical environments like substations, power plants, and industrial factories. Unlike a single rod, a grid provides multiple parallel paths to the ground, ensuring system reliability even if one part of the network is damaged.
Key Components and Design
- Grid Structure: Typically constructed using copper-bonded steel strips, solid copper, or galvanized iron (GI) mesh. The size and density of the grid are determined by a "soil resistivity test" to ensure the resistance remains below 1 ohm for critical systems.
- Interconnections: Joints are often made using exothermic welding (cad-welding) rather than mechanical clamps. This creates a permanent molecular bond that won't corrode or loosen over decades of underground service.
- Step and Touch Potential Control: The primary engineering goal is to limit the voltage difference between a person’s feet (step) or between their hands and a grounded object (touch) during a short circuit.
Primary Types
- Horizontal Mesh Grids: Used beneath concrete floors in substations to create an equipotential zone, ensuring the entire floor remains at the same voltage.
- Plate-Type Earth Mats: Large copper or GI plates used in areas with limited space or extremely high soil resistivity.
- Lattice Earth Mats: Prefabricated mesh designs, like those from nVent ERICO, which are faster to install than manual strip-laying.
