ACAR Conductor (Aluminium Conductor Alloy Reinforced)

How ACAR works

Every overhead conductor balances two jobs: carrying current with low loss and holding mechanical tension across the span. AAC (all 1350) is excellent at the first and weak at the second. AAAC (all 6201) is strong but about 15 % more resistive. ACSR uses a steel core for strength. ACAR blends the two aluminium wires in one concentric construction, so the designer can choose almost any point between AAC and AAAC.

In most ACAR constructions the 6201-T81 wires form the centre and inner layers and the 1350-H19 wires form the outer layers, although ASTM B524 permits other arrangements. Because all wires have the same diameter and the same density, the conductor is geometrically identical to an AAC or AAAC of the same size and uses the same fittings, dampers and stringing practice.

The ACAR concept is popular where utilities want better strength than AAC without introducing steel, for example on coastal distribution and sub-transmission lines, or where a line must be re-conductored on existing structures that cannot carry the weight of a heavier ACSR.

ACAR stranding and wire materials

Examples of common constructions. ASTM B524 tabulates many combinations by size; the designer or utility selects one from the line study.

How the wire ratio changes resistance

Consider a 37-wire conductor with every wire 3.00 mm in diameter (7.07 mm² each, about 262 mm² in total). Using minimum conductivities of 61.0 % IACS for 1350 and 52.5 % IACS for 6201, the approximate DC resistance at 20 °C, including about 2 % for stranding lay, is:

Each 6201 wire carries roughly twice the tensile load of a 1350 wire of the same size, so moving from 30/7 to 18/19 raises rated strength markedly while increasing resistance by only about 5 %. Those figures are illustrative; the rated breaking strength, resistance and mass of a real conductor come from the tables of the standard named in the specification.

ACAR compared with AAC, AAAC and ACSR

A common misconception is that ACSR has "higher conductivity" than ACAR. It does not: the steel core adds strength but carries almost no current. Two conductors with the same aluminium area have similar resistance, and the ACSR is heavier. ACAR's limitation is strength and high-temperature sag, not conductivity.

Where ACAR is used

• Medium-span transmission and sub-transmission: where AAC would sag too much but steel is not wanted
• Coastal and industrial areas: all-aluminium construction avoids corrosion of a steel core in salt or chemical pollution
• Re-conductoring: raising capacity on existing structures with limited load capacity
• Lines sensitive to losses: no magnetic losses and a chosen balance of resistance and strength
• Industrial and mining networks: long-life overhead distribution where maintenance access is difficult

Standards and specifications

Ampacity depends on conductor resistance, diameter, surface condition, ambient temperature, wind speed and solar radiation; it is calculated for each project using IEEE 738 or CIGRE methods rather than taken from a catalogue table.

Supply, testing and packing

Related conductors and materials

ACAR conductor: frequently asked questions