Earthing (grounding) is one of the most safety-critical parts of any electrical installation, yet it's often the least visible — buried electrodes and cable connections rarely get a second look once commissioned. Here's why it matters and what to know.
Why Earthing Matters
- Shock protection: Provides a low-resistance path for fault current to flow back to source, allowing protective devices (fuses, breakers, RCDs) to operate quickly and disconnect a faulty circuit before it becomes a serious shock hazard.
- Equipment protection: Limits the voltage that can appear on exposed metal parts (enclosures, frames) during a fault, protecting both equipment and personnel.
- Stable reference: Gives the electrical system a stable zero-voltage reference point, important for consistent protection relay operation and equipment performance.
- Lightning and surge protection: Provides a discharge path for lightning strikes and switching surges, reducing damage to sensitive equipment.
Common Earthing System Types (per IEC 60364)
- TN-S: Separate neutral and protective earth conductors throughout — common in industrial installations with a dedicated earth conductor run alongside supply cables.
- TN-C-S: Combined neutral-earth conductor from the source, split into separate neutral and earth within the installation — common in many LV distribution systems.
- TT: The installation has its own local earth electrode, independent of the supply's earthing — common where the supply authority doesn't provide a reliable earth terminal.
- IT: The system has no direct connection to earth (or only through high impedance) — used in specific applications like hospital operating theatres or process plants where a single earth fault shouldn't cause immediate disconnection.
Earth Electrodes
Common electrode types include earth rods (copper-bonded steel, driven vertically), earth plates, and earth mats (grids of buried conductor, common in substations for step/touch voltage control). Multiple electrodes are often bonded together to achieve a lower overall earth resistance than any single electrode.
Earth Resistance Testing
Periodic testing (typically annually) using an earth resistance tester (fall-of-potential method or clamp-on tester) confirms the earthing system still provides a sufficiently low resistance path — soil conditions, corrosion, and connections can degrade earth resistance over time even if the installation is otherwise unchanged. Acceptable resistance values depend on the application and local code requirements, but lower is generally better for both safety and equipment protection.
Common Mistakes
- Relying on a single earth electrode with no bonding to a second electrode or the building's structural steel.
- Loose or corroded earth connections at equipment enclosures — a visual inspection during routine maintenance catches this early.
- Undersized earth conductors relative to the fault current they may need to carry.
TEKTOW supplies earthing accessories, CT/PT, and protection equipment for industrial installations. Get in touch for your earthing system requirements.