GI vs copper vs copper-bonded earthing electrodes: which should you specify?
How galvanised iron, pure copper and copper-bonded steel electrodes differ in conductivity, corrosion life, installation and cost, and how to choose for your soil and fault level.
Ashima Electrotech technical team · 4 min read
Short answer: GI is the economical choice for general LV work in non-aggressive soil. Pure copper gives the longest corrosion life and is used where fault currents are high or the soil is aggressive. Copper-bonded steel combines copper's surface with a steel core, so it can be driven deep and costs less than solid copper. For long life, specify a copper coating of at least 250 µm.
An earth electrode has one job: give fault and leakage current a low-resistance path into the ground, and keep doing it for the life of the installation. The material decides how long it keeps doing that. The three options most Indian projects choose between are galvanised iron (GI), pure copper, and copper-bonded steel.
How the three compare
| Property | GI | Pure copper | Copper-bonded steel |
|---|---|---|---|
| Conductivity | Lowest of the three | Highest | Copper surface, steel core |
| Corrosion resistance | Depends on zinc coating; weakest in acidic, saline or wet clay soils | Best | Good, as long as the copper layer stays intact |
| Mechanical strength | Good | Soft; not driven, usually set in a pit or bore | High; can be driven to depth |
| Relative cost | Lowest | Highest | Between the two |
| Typical use | Homes, small commercial, LV equipment earthing | Substations, transformer neutrals, high fault levels, aggressive soil | Solar plants, telecom, industrial, lightning protection earths |
GI electrodes
A galvanised pipe is protected by its zinc coating. Hot-dip galvanising matters, because it covers cut ends and drilled holes as well as the outer surface. GI works well in neutral, well-drained soil. In acidic soil, saline soil, or soil that stays wet and clayey, the zinc is consumed faster and the steel underneath starts to corrode. Once that happens, earth resistance rises.
GI is the right answer when the budget is tight, the soil is not aggressive, and the electrode can be inspected and replaced over the life of the building.
Pure copper electrodes
Copper has the best conductivity and the best corrosion resistance of the three. It is the usual choice where the electrode carries high fault currents, such as transformer neutrals, substations and large industrial panels, or where the soil would quickly attack GI. Copper is soft, so a copper pipe electrode is set into a pit or bore and backfilled rather than hammered in.
Copper-bonded steel rods
A copper-bonded rod is a high-strength steel core with copper bonded to its surface, usually by electrolytic deposition. The steel lets the rod be driven to depth, often in coupled lengths, to reach the lower, more stable resistivity soil below the surface. The copper gives the corrosion behaviour of copper at the surface.
The coating thickness is what decides service life. IEC 60364-5-54 calls for at least 250 µm of copper on steel earth rods. Thin-coat rods, around 40 to 50 µm, cost less but have far less copper to lose before the steel is exposed. ACME copper bonded rods come in both classes, 40–50 µm and 250–270 µm. Specify the thicker class wherever the specification references these standards, or where the rod is expected to last decades in the ground.
Questions to answer before you choose
- What is the soil like? Measured soil resistivity, plus whether the soil is acidic, saline or waterlogged.
- What fault current must it carry, and for how long? This sets the conductor and electrode cross-section.
- What resistance does the specification or authority require? Values differ by installation type, so take the number from your project specification.
- How deep can you go? Rock or a shallow water table changes the choice between driven rods, pipe electrodes in a bore, or several shallower electrodes in parallel.
- How long must it last without replacement? This often tips the decision from GI to copper or copper-bonded.
Where backfill fits
In high-resistivity soil, such as rocky, sandy or dry ground, the electrode alone may not reach the target resistance. Backfilling the bore with an earth enhancement compound lowers the resistance at the electrode surface and holds moisture around it. It is often cheaper than adding more electrodes. See our guide to earth enhancement compound.
ACME electrodes
Ashima Electrotech manufactures ACME pipe electrodes in GI pipe-in-pipe, GI pipe with GI or copper strip, pure copper pipe with copper strip, and copper-bonded configurations, in 50 and 80 mm diameters and 2 and 3 m lengths. We also make copper bonded rods in 14 and 17.2 mm diameters and 1 to 3 m lengths. Every catalogue code is listed on the Earthing Systems page.
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Products mentioned
General technical guidance, not a design for a specific site. Follow your project specification, the current editions of the applicable standards and the requirements of the inspecting authority.