0.25 mm plated copper-clad steel wire as horizontal earthing: usable, and not

Appendix to the Copper-Clad Steel Earthing Selection Guide · Supply position 1 / 3

The conclusion first: 0.25 mm electroplated copper-clad steel round wire as a horizontal earthing conductor – we supply it, and we do not recommend it. When people ask whether it "can be used", both answers are right. It can, because it has twenty years of project history. It should not, because the place those twenty years finally gave it is no longer "first choice for horizontal conductor". Here are both sides, so that the designer can decide.

1. Usable: it has a real history, and it is still in use

Copper-clad steel earthing in China began with 0.25 mm electroplated product. The company that brought it in, built the first demonstration projects and persuaded design institutes for the first time that a steel core with a copper layer could serve as an earthing conductor was ERICO. We entered the industry after that, and the thick-layer continuous-cast product we make today follows the road they opened. We acknowledge that here.

0.25 mm plated wire is still used in China – mainly in low-corrosivity soil, for equipotential bonding and where the design life is modest. It is also used in a number of countries in Asia and Africa, and that is directly linked to Chinese EPC exports: the contractor takes the sizes it is used to at home, the local code has nothing more specific, and 0.25 mm stays. So where a project is specified at 0.25 mm, or the soil is genuinely low-corrosivity and the design life short, it can be used, and we supply it.

2. Not recommended: after twenty years, its position has changed

2.1 The Chinese codes left it in the middle: less economical than galvanised steel, less reliable than thick-layer

DL/T 2650-2023, the technical-supervision guide for earthing metals in power projects, is the Chinese power industry's final word on material selection: hot-dip galvanised steel for low-corrosivity soil; 0.6 / 0.8 mm copper-clad steel for medium and high corrosivity (alongside copper at high). There is no line for 0.25 mm. In low-corrosivity soil galvanised steel is enough and cheaper; in medium and high, 0.25 mm is not enough. At the same time both copper-clad steel product standards – DL/T 1312-2023 and State Grid's Q/GDW 10466-2021 – recommend the annealed soft temper for horizontal conductor after their revisions, and electroplating cannot deliver an annealed product (the heat breaks the plated bond). That is what we mean by "its position changed": it did not fail; after years of practice the codes found a better material at each end.

2.2 The US: UL 467 has no category for plated-steel horizontal electrodes, and the reason is the NEC

Overseas buyers often ask whether our wire is UL listed. Frankly, no – and nobody's is, because UL 467 has no category of "copper-clad steel horizontal earthing conductor". The reason lies not with UL but with the NEC: NEC 250.52(A)(4) requires a ground ring to be a copper conductor not smaller than 2 AWG; 250.62 limits grounding electrode conductors to copper, aluminium or copper-clad aluminium; copper-coated steel is recognised only in 250.52(A)(5), for rod electrodes. UL 467 lists equipment for use under the NEC; where the NEC has no place for a copper-clad steel horizontal conductor, UL has nothing to list. (Substations are outside the NEC, and IEEE 80 Table 1 does carry constants for copper-clad steel wire – so US utilities can use it in substation grids, but that is a different system.)

2.3 The practical problems

• Too thin to be dragged. A 0.25 mm plating is easily scored down to bare steel when the wire is dragged along a trench over stones or rebar. Bare steel next to copper forms a corrosion cell; the core corrodes from the scratch outward, and after backfill nobody sees it.
• Cannot be annealed, so it is hard to lay. A plated layer does not survive annealing, so 0.25 mm plated wire is supplied hard-drawn. Hard wire springs back when bent, will not hold its shape in the trench, and is awkward to align for exothermic welding; site crews call it hard work. The codes' preference for the annealed temper is aimed at exactly this.
• Almost no corrosion allowance. Sizing the copper layer as corrosion rate × design life, 0.25 mm does not cover thirty years in medium-corrosivity soil – and that is before the scratches above.

3. What we do about it

We keep 0.25 mm plated round wire, tape and rods in the range for three reasons: some specifications call for 0.25 mm; low-corrosivity soil and equipotential bonding genuinely use it; and rods are electroplating's home ground anyway. But when a customer asks what to use for horizontal conductor, our recommendation is 0.6 / 0.8 mm continuous-cast, annealed round wire – not because it costs more, but because twenty years and millions of kilometres of Chinese practice ended there. In the free assessment we put the two options side by side: what 0.25 mm costs and how long it lasts; what 0.6 / 0.8 mm costs and how long it lasts. Which to choose is the designer's and owner's decision. Setting out both sides is ours.