Standard Specification for Concentric-Lay-Stranded Aluminum 1350 Conductors (AAC) — the governing North American specification for bare all-aluminum overhead phase conductors built from hard-drawn EC-grade aluminum 1350-H19 wires, offering the highest electrical conductivity of any mainstream overhead conductor family.
ASTM B231 covers bare concentric-lay-stranded conductors made entirely from hard-drawn aluminum 1350 wires (per ASTM B230), constructed with a straight round central wire surrounded by one or more helically-applied wire layers. Unlike ACSR (B232) or ACS (B416), AAC contains no steel core and no bimetallic wires — every wire is pure EC-grade aluminium, giving the conductor the highest current-carrying capacity per unit weight of any ASTM overhead conductor family.
AAC is the workhorse phase conductor for urban and suburban overhead distribution (typically ≤69 kV), short transmission spans, substation bus work, and aerial feeders in coastal and industrial atmospheres where the absence of a steel core eliminates galvanic corrosion risk. Because its low tensile strength limits span length, AAC is generally preferred where supports are closely spaced and mechanical loading is moderate. Higher-strength overhead applications usually specify AAAC (B399), ACSR (B232), or ACSR/AW (B549) instead.
AAC per ASTM B231 is a homogeneous concentric-lay-stranded conductor. All wires share the same aluminum 1350 material and the same nominal diameter within a given size. Successive layers are helically applied with alternating lay direction; the direction of the outer layer is right-hand for Classes AA and A and left-hand for Classes B, C, and D.
Each wire is round, solid, and drawn from 99.5%+ pure electrical-grade aluminium (UNS A91350). 1350-H19 wire meets ASTM B230/B230M: minimum 61.2% IACS conductivity and specified minimum tensile strength that decreases slightly with increasing wire diameter.
A single central wire with each successive layer having 6 more wires than the previous. Standard configurations: 7 (1+6), 19 (1+6+12), 37 (1+6+12+18), 61 (1+6+12+18+24), and 91 wires. Adjacent layers have opposite lay direction to prevent birdcaging.
Class AA is the standard class for bare overhead lines and specifies 1350-H19 wire. Class A is used for covered conductors and flexible bare conductors (also 1350-H19). Classes B / C / D offer progressively greater flexibility for insulated cable applications, with tempers H14/H16/H24/H26 as appropriate.
Cold-pressure or resistance-butt welds in individual aluminum wires before stranding are permitted, provided no two joints occur within any single wire layer at the same cross-section and the welded-wire tensile strength meets the specification minimum. This distinguishes AAC from B416 ACS, which allows no wire joints.
Representative Class AA (bare overhead) sizes with standard flower code names per Aluminum Association Publication No. 50. Rated breaking strength (RBS) is calculated from the sum of component wire strengths per ASTM B230. DC resistance corrected to 20 °C.
| Code Name | Size (AWG / kcmil) | No. of Wires | Wire Dia. (mm) | OD (mm) | Mass (kg/km) | RBS (kN) | DC Resist. (Ω/km @ 20 °C) |
|---|---|---|---|---|---|---|---|
| Rose | #6 AWG | 7 | 1.38 | 4.14 | 18.3 | 1.94 | 2.173 |
| Iris | #2 AWG | 7 | 2.47 | 7.41 | 58.5 | 5.73 | 0.6832 |
| Poppy | #2/0 AWG | 7 | 3.78 | 11.35 | 137.5 | 13.5 | 0.2908 |
| Phlox | #4/0 AWG | 7 | 4.77 | 14.31 | 218.9 | 20.7 | 0.1828 |
| Daisy | 266.8 kcmil | 7 | 5.89 | 17.66 | 334.6 | 28.6 | 0.1196 |
| Tulip | 336.4 kcmil | 19 | 3.85 | 19.27 | 424.6 | 40.9 | 0.09488 |
| Cosmos | 477 kcmil | 19 | 4.59 | 22.95 | 602.4 | 55.6 | 0.06691 |
| Mistletoe | 556.5 kcmil | 37 | 3.55 | 24.88 | 704.9 | 66.7 | 0.05736 |
| Orchid | 636 kcmil | 37 | 3.80 | 26.60 | 805.0 | 76.1 | 0.05021 |
| Lilac | 795 kcmil | 61 | 3.32 | 29.90 | 1008 | 97.3 | 0.04017 |
| Bluebell | 1033.5 kcmil | 61 | 3.78 | 34.05 | 1308 | 126.3 | 0.03090 |
| Columbine | 1351.5 kcmil | 61 | 4.32 | 38.86 | 1711 | 165.1 | 0.02361 |
ASTM B231 requires the following tests on individual 1350-H19 wires (per ASTM B230) and on the completed stranded conductor:
AAC per ASTM B231 remains the conductor of choice for overhead distribution in urban, suburban, and coastal networks where spans are short, wind and ice loading is moderate, and the galvanic corrosion of an ACSR steel core would shorten service life. Utilities across North America, the Caribbean, the Middle East, Southeast Asia, and Africa routinely specify AAC for 11–33 kV feeders in salt-fog and industrially polluted atmospheres, and for low-voltage aerial mains in densely built urban grids. Because AAC's rated breaking strength is significantly lower than ACSR or AAAC of equivalent cross-section, span selection and sag-tension design are tighter — but when spans and loadings allow it, AAC delivers the maximum current-carrying capacity per kilogram of any ASTM-rated overhead conductor, making it the most material-efficient choice for the electrical duty it is designed to perform.
Official Standards & References
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