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Grades and construction
Three conductivity grades, each with a controlled copper volume around a steel core.
The three grades
| Grade | Copper volume | Where it is used |
|---|---|---|
| 21% IACS | 10% – 20% by volume | Grounding, guy strand, overhead ground wire |
| 30% IACS | 20% – 30% by volume | Coaxial drop wire, CATV messenger, shield wire |
| 40% IACS | 30% – 40% by volume | RF feedline, weight-critical conductor |
Conductivity and copper volume are not the same number and are not interchangeable. Two constructions can reach the same IACS with different cladding thickness, and the thinner cladding is the one that fails first at a cut end or in a corrosive run.
Construction
| Core | Steel, grade per the tensile the application needs |
| Cladding | Copper, metallurgically bonded, concentric |
| Ratio | Controlled per lot and measured on a cross-section |
| Standard | ASTM B227 / B452 |
Why copper-clad steel instead of solid copper
- Higher tensile for the same diameter, so a messenger or guy strand spans further without extra support.
- Less copper by weight for the same surface conductivity, which is the reason the grade exists.
- The steel core carries the mechanical load; the copper carries the current, and both are stated separately on the certificate.