Standard Specification for Concentric-Lay-Stranded Aluminum Conductors, Aluminum-Alloy Reinforced (ACAR, 1350/6201) for use as bare overhead electrical conductors in transmission and distribution lines, offering a fully steel-free, lightweight, high-conductivity solution.
ASTM B524/B524M covers concentric-lay-stranded conductors made entirely from aluminium — round 1350-H19 extra-hard aluminum wires concentrically stranded around a core of round 6201-T81 aluminum-alloy wires — for use as bare overhead electrical conductors.
Unlike ACSR, AACSR, ACSS, and ACSR/AW, ACAR contains no steel whatsoever. The 6201-T81 alloy core wires provide mechanical reinforcement, while the 1350-H19 outer wires maximize electrical conductivity. This design eliminates all magnetic hysteresis and eddy current losses associated with steel cores, giving ACAR the highest ampacity-to-weight ratio of any steel-reinforced or alloy-reinforced overhead conductor family. Although the alloy strands typically form the core, the standard permits mixed configurations where 6201-T81 wires are distributed throughout the cross-section.
ACAR is an all-aluminium composite conductor. The 6201-T81 core wires bear mechanical tensile load by virtue of their higher proof strength, while the 1350-H19 outer wires deliver maximum electrical current capacity. Both wire types are round and of the same nominal diameter within a given stranding configuration.
Round aluminum-magnesium-silicon alloy 6201-T81 wires, solution heat-treated, cold-worked, and artificially aged. Minimum tensile strength 295 MPa, minimum 52.5% IACS conductivity. Provides mechanical reinforcement without a steel core. Complies with ASTM B398.
Round extra-hard (H19 temper) aluminum 1350 wires concentrically stranded around the alloy core. Minimum 61% IACS conductivity. Common stranding configurations include 4/3, 12/7, 16/19, 26/7, 30/7, 54/7, and 54/19 (1350/6201 wire counts). Complies with ASTM B230.
The proportion of 6201-T81 to 1350-H19 wires can be varied to balance mechanical strength against electrical conductivity. Higher 6201 content increases rated breaking strength; higher 1350 content increases ampacity. The standard covers both Table 1 (inch-pound) and Table 2 (SI metric) size series.
6201-T81 core wires undergo solution heat treatment → cold working → artificial aging before stranding. Wire joints (electric-butt welds, cold-pressure welds) are permitted in individual wires during stranding; no joints in the finished conductor.
Representative sizes from ASTM B524. Each size is available in multiple stranding configurations varying the 1350/6201 wire ratio to suit project-specific strength or conductivity requirements.
| Size (kcmil/AWG) | Stranding (1350/6201) | Nom. OD (mm) | Mass (kg/km) | RBS (daN) | DC Resist. (Ω/km @ 20 °C) |
|---|---|---|---|---|---|
| 266.8 | 16/3 | 16.8 | 368 | 4,880 | 0.231 |
| 400 | 12/7 | 18.44 | 560 | 4,230 | 0.135 |
| 500 | 30/7 | 20.65 | 700 | 4,795 | 0.117 |
| 795 | 24/13 | 26.0 | 1,112 | 9,000 | 0.0741 |
| 954 | 42/7 | 28.5 | 1,330 | 8,760 | 0.0617 |
| 1,100 | 42/19 | 30.70 | 1,540 | 11,010 | 0.0534 |
| 1,800 | 54/7 | 39.30 | 2,520 | 15,140 | 0.0326 |
ASTM B524 specifies the following mandatory tests for both individual wires and the completed conductor:
ACAR per ASTM B524 is extensively specified for high-voltage and extra-high-voltage (EHV) transmission lines where minimising resistive and magnetic losses directly reduces energy operating costs over a 40+ year asset life. Because there is no steel core, ACAR produces no AC magnetic core losses — a meaningful efficiency advantage on large conductors at high current densities. The adjustable 1350-H19 / 6201-T81 wire ratio allows engineers to optimise each project for the specific combination of mechanical sag requirements, conductor weight, and ampacity, without changing the overall conductor diameter or hardware.
Official Standards & References
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