Construction: solid conductor vs strand
Copper-clad steel selection guide, part 3 of 8
Rule: where a solid conductor (round or flat) will do, do not use strand. For the buried electrode, solid first; for the bonding conductor between electrode and equipment – mostly at or near the surface – strand may be used where it helps. Based on ASTM B227-04, DL/T 1312-2023, DL/T 2727-2023 and project experience.
Solid conductor – first choice
- Better corrosion resistance. At equal cross-section and copper content, strand has a thinner copper layer, and the more wires the thinner it gets; solid has the thickest.
- Lower cost. Formed in one pass; strand needs single wires first, then stranding and straightening.
- Verifiable quality. Copper thickness is the decisive quality parameter. On solid conductor a hand-held coating gauge measures it on site; on strand it cannot be measured once stranded, and the single wires are below the range of ordinary gauges.
Strand – where it helps
- Its advantage is flexibility. Far more flexible than solid at the same cross-section – tight spaces between equipment and electrode, awkward corners.
- For bonding conductors, not for the buried electrode. Acceptable where corrosion demands are moderate.
- Specify the minimum copper thickness per wire. On strand marked "≥ 0.25 mm" the actual thickness follows from conductivity grade and wire diameter; 0.25 is only the floor.
At equal total section and copper fraction, dividing into more wires of equal diameter reduces the absolute copper thickness per wire; fixing the per-wire thickness instead gives a different comparison. The number of wires alone does not set the life – the minimum copper thickness per wire does. This is why our IEEE P80 contribution asks that strand be specified by number of wires, wire diameter and per-wire minimum copper thickness.
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