Why we supply electroplated copper-clad steel tape but do not recommend it

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

Conclusion: where the drawings specify electroplated copper-clad steel flat tape, we supply it and it is accepted to the standard; but we do not recommend choosing it. The shape of a tape and the electroplating process together bring four problems – uneven copper thickness, extra copper spent to protect the thinnest point, cracking at the edges when bent, and poor fit in the exothermic welding mould. For horizontal conductor we recommend round wire of the same section instead.

1　Why plated tape is thick at the corners and thin in the middle

In electroplating the current is not evenly distributed over the workpiece: at edges and corners the field lines concentrate, the current density is high and copper deposits fast; at the middle of a broad face the current density is low and it deposits slowly. This is the edge effect of electroplating. A round wire has the same curvature everywhere and no edges, so its copper is naturally uniform; a tape has four edges, and the finished product is inevitably thick at the corners and thin at mid-face.

Auxiliary cathodes, shields, anode placement and current waveform control reduce the unevenness a great deal, but cannot remove it. It takes experience: in years of production we have brought the thick–thin difference down to a level at which exothermic welding is not affected. That is not the general level of plated tape, and how far any product on the market controls it depends on the maker's process.

2　To protect the thinnest point the corners must be thicker – more copper, higher cost

Copper thickness is accepted on the minimum at any measuring point (DL/T 1312: three sections, three points each, minimum taken). What sets the life of a tape is the thinnest point at mid-face. To bring that point to 0.25 mm the corners have to be plated noticeably thicker, and that extra copper adds cost without adding life. The same copper on a round wire is spread evenly: minimum and average are almost the same.

3　The edges crack more easily when bent

Tape is bent on site to change direction. In bending, the outer fibres stretch most, and the edges sit exactly where the strain is highest – which is also where the plated layer is thickest. Plated copper is not annealed and has limited ductility, so the thick parts crack more readily at the edges. Once the copper cracks, the steel core is in direct contact with the soil, corrosion starts at the crack, and the life of that length is no longer governed by copper thickness.

4　Exothermic welding: the mould bears on the corners and leaves a gap at mid-face

Welding moulds are machined to nominal size. With a tape that is thick at the corners and thin at mid-face, the closed mould bears on the four corners and leaves a gap between the broad face and the mould. During the weld, molten metal leaks through the gap; the joint is not full, the enclosure is incomplete and weld quality suffers (figure ②). With the thick–thin difference under control the problem is avoided – our tape achieves this; with a poorly controlled product it shows up only when welding on site. Round wire meets the mould on a curved surface and has no such problem.

5　Rolling round wire into tape does not help either: 30–50 % less copper

There is another way to make tape: rolling copper-clad steel round wire flat. The same material, flattened, has a longer perimeter, so the copper layer is spread 30–50 % thinner and corrosion resistance falls accordingly. For example, a Ø 14 / 0.8 mm round wire rolled to a 30:4 tape keeps only about 0.44 mm of copper even under the most favourable assumption of an even layer; in real rolling the broad faces are thinner still, and the minimum point smaller. The calculation is in round wire vs flat tape.

6　Our recommendation

• Use round wire for horizontal conductor. Choose the diameter from the thermal-stability section, and the copper layer from the soil corrosivity class – 0.6 / 0.8 mm continuous-cast, annealed. The equal-section substitution table is in round vs flat; in the assessment we work it out for your project.
• Where the drawings require tape, we supply it: copper declared and accepted on the thinnest point at mid-face of the finished product, with the thick–thin difference held to a level that does not affect exothermic welding. Whoever you buy from, write "minimum copper thickness at any measuring point" into the specification and spot-check the mid-face on delivery.
• For low-corrosivity soil and vertical electrodes only, the 0.25 mm plated ground rod (round) remains a mature and reasonable choice – the problem lies in the tape shape, not in electroplating itself.