What earthing and bonding do
Earthing connects the installation to the general mass of earth through electrodes. Bonding connects exposed and extraneous metal parts (frames, pipes, structural steel, cable tray) together so they stay at the same potential. Together they let the protective device disconnect a fault quickly, as IEC 60364-4-41 requires, limit the voltage a person can touch, give a stable reference for instruments and electronics, and carry lightning and static charges safely away.
Electrodes, conductors and bars
| Component | Notes |
|---|---|
| Copper-bonded steel rods | The most common electrode: steel strength with a copper layer against corrosion; can be coupled to drive deeper. Components for lightning protection earthing are covered by IEC 62561-2 |
| Solid copper or stainless rods | For aggressive soils where long life matters |
| Earth plates | Where rods cannot be driven, for example on rock |
| Copper tape or bare conductor | Laid in a trench as a ring or mesh around a building or plant area |
| Main earth bar and test link | Collects the earthing and bonding conductors; the link lets an electrode be disconnected for testing |
| Inspection pits | Give access to rod connections for inspection and measurement |
Joints below ground are made with rated clamps or exothermic welds. Conductor sizes are set by the design to IEC 60364-5-54.
Soil resistivity: why Saudi sites read high
Earth resistance depends mostly on the soil. Dry sand, gravel and rock have high resistivity, and resistivity rises further as the soil dries and heats in summer. Measure soil resistivity before the design, usually with the four-pin (Wenner) method, so the electrode layout is based on real data.
- Go deeper: coupled rods reach lower, moister layers with more stable resistivity.
- Use more rods: rods in parallel lower the resistance, but only if they are spaced apart, typically by at least their driven length, so their resistance areas do not overlap.
- Use enhancement compounds: low-resistivity backfill around rods and conductors (see IEC 62561-7) improves contact with the soil. Avoid salt and charcoal, which corrode the electrode and wash away.
What earth resistance should you aim for?
There is no single legal figure that applies to every site. Many project specifications ask for values in the range of about 1 to 5 Ω, depending on the system, with lower values for substations and sensitive installations. The project specification, the utility's requirements and the designer decide the target. Two standard rules are useful:
TT systems with RCDs (IEC 60364-4-41): RA × IΔn ≤ 50 V
For lightning protection, IEC 62305-3 recommends a low earthing resistance, if possible below 10 Ω measured at low frequency. Our earthing calculator estimates the resistance of rods from soil resistivity and rod size.
How to measure
- Fall-of-potential (three-pole): a current spike is driven well outside the electrode's resistance area and a potential spike is placed at 62 % of that distance. Move the potential spike about 10 % of the distance either way; if the readings stay close, the result is valid. The electrode under test is usually disconnected at the test link, with the installation made safe first.
- Clamp-on (stakeless) tester: measures without spikes or disconnection, but only where there is a parallel return path through other earths, such as a multi-earthed system. It cannot test a single isolated rod.
- Continuity of bonding: a low-resistance ohmmeter checks protective and bonding conductors from the main earth bar to each item.
Periodic inspection and testing
Earthing degrades quietly: connections corrode, tapes are cut during civil works, links are left open. Periodic verification under IEC 60364-6, and inspection of lightning protection under IEC 62305-3, should include a visual check of pits, clamps and labels, measurement of each electrode and of bonding continuity, and a written record with the date and soil conditions. Compare each result with the first one; a steady rise points to corrosion or a broken joint. Testing at the end of the dry season shows the worst case. The interval follows the owner's maintenance plan and the project specification.
Lightning protection and surge protection
The earth termination of a lightning protection system (IEC 62305) must be bonded to the installation's main earthing so that the whole site rises together during a strike; separate, unconnected earths create dangerous voltages between them. Surge protective devices on incoming power and data lines complete the protection.
What to send us for a quotation
Rod diameter and length, couplers and driving heads, clamps, tape or conductor size and length, earth bars and test links, inspection pits, enhancement compound, and any testers you need (fall-of-potential, clamp-on, low-resistance ohmmeter). If you have soil resistivity data and a target value, send them with the drawing and we quote the complete material list.
Common questions
What is the maximum allowed earth resistance?
There is no single value for every site. Many specifications ask for about 1 to 5 Ω depending on the system; the project specification, utility rules and the designer set the target.
Why is earth resistance high on sandy sites?
Dry sand has high resistivity, and it rises further in summer. Deeper rods, more rods spaced apart and enhancement compounds lower the resistance.
Can a clamp-on tester replace the three-pole method?
Only where a parallel earth return path exists. It is quick for periodic checks on multi-earthed systems, but cannot measure a single isolated electrode.
Need these items? Send your list or a nameplate photo; your quotation arrives within 24 hours.
This guide is general information. Final selection must follow the project design, the applicable standards and the maker's data.