Galvanized steel wire strand for ACSR (Aluminum Conductor Steel Reinforced) conductors is specified to ASTM A475 Class A or Class B. This guide compares the two classes on strength, zinc coating and typical applications, with selection guidance for transmission line and distribution conductor projects.
ACSR conductor uses a galvanized steel wire strand as the core that carries the mechanical load, while the outer aluminum strands carry the current. The galvanizing protects the steel core from corrosion, which is the dominant failure mode for ACSR in service. ASTM A475 covers the zinc-coated steel wire strand used in ACSR, and the Class designation (A, B, or C) refers to the zinc coating weight per unit length of wire, not to the strength grade. Choosing between Class A and Class B is one of the most consequential specification decisions for ACSR conductors.
What ASTM A475 Class A and Class B Specify
ASTM A475 Class A is the lightest zinc coating of the three classes, with minimum coating weights ranging from about 0.15 oz/ft² (46 g/m²) for the smallest wire sizes to 0.40 oz/ft² (122 g/m²) for the largest. Class B is heavier, with coating weights roughly 2.0 to 2.5 times Class A, ranging from about 0.30 to 1.00 oz/ft² (92 to 305 g/m²). Class C is the heaviest, used for the most corrosive environments. The wire strength grade (Common, Siemens-Martin, High-Strength, Extra High-Strength) is specified separately from the coating class.
When Class A Is the Right Specification
Class A galvanized wire strand is the right specification for ACSR conductors in dry inland environments, for distribution lines in temperate climates, and for any application where the conductor will see minimal chloride or industrial pollution exposure. Class A is the most widely specified class globally because the majority of transmission and distribution networks are in environments where the lighter coating is adequate for the 40–50 year design life of the line.
When Class B Is the Necessary Upgrade
Class B galvanized wire strand is the right specification for ACSR conductors in coastal regions (within roughly 5 km of the sea), in industrial areas with sulfur or chloride pollution, in humid tropical climates, and for transmission lines designed for 60–80 year service life. The heavier coating doubles or triples the time to first corrosion of the steel core, which is the critical failure mode for ACSR. For long river crossings, heavy industrial corridors, and any project where line replacement cost is very high, Class B is the conservative specification.
Strand Construction and Wire Strength Grade
ACSR core strand is typically 7-wire (1x7) or 19-wire (1x19) construction, with wire diameters from 2.0 mm to 4.0 mm. The wire strength grade (Common at 1,240 MPa minimum tensile, Siemens-Martin at 1,520 MPa, High-Strength at 1,720 MPa, Extra High-Strength at 1,960 MPa) is selected based on the mechanical load on the conductor: long spans, heavy ice load, or wide river crossings require higher strength grades. The zinc coating class and the wire strength grade are independent specifications, and both should be stated explicitly in the RFQ.
What to Specify on the ACSR Strand RFQ
State the standard (ASTM A475), the coating class (A, B, or C), the wire strength grade (Common, Siemens-Martin, High-Strength, or Extra High-Strength), the strand construction (1x7 or 1x19), the wire diameter or the overall strand diameter, the reel weight, and the lay direction (right or left lay). For most transmission and distribution projects in temperate climates, Class A Common grade is the standard; for coastal or industrial environments, default to Class B. Always confirm the mill supplies the test report per EN 10204 3.1 with the actual zinc coating weight and the strand breaking strength.
Related Resources from Baobin Steel
- Steel wire catalog – galvanized strand and ACSR wire
- Mild steel overview – grades and standards
- Request a quote – send your conductor spec for ACSR strand pricing