ACSR or AAAC: identifying overhead conductor

Two ways to make a conductor strong

ACSR is aluminum conductor steel reinforced. Stranded electrical-grade aluminum carries the current and a central steel core carries the tension. The core is galvanized, aluminized or aluminum-clad, and that choice matters more on the coast than anywhere else. The ratio of aluminum to steel sets both the strength and the weight per foot.

AAAC is all-aluminum alloy conductor. There is no steel. Every strand is 6201 aluminum alloy, a magnesium-silicon alloy heat treated to a temper that makes it considerably stronger than plain electrical-grade aluminum. The conductor is homogeneous from the surface to the centre, which removes the dissimilar-metal couple entirely.

A third family causes most of the mislabelling. ACAR is aluminum conductor alloy reinforced: 6201 alloy strands over a core of plain aluminum strands. It has no steel but it is not AAAC either, and a stranding that reads like a core and layers is the clue.

The reel settles more arguments than the surface does. ACSR tags usually carry a code word and the stranding together, and the code word alone is enough if the reader has the table. AAAC tags tend to name the alloy, 6201, with a single-number stranding. Where the tag is gone, the cut end answers in a minute and photographs well.

Stranding is the identifier

Overhead conductor is written as aluminum strands over core strands. A two-part number is reinforced; a single number is homogeneous. That is the whole rule, and it is printed on the tag in a form that does not decay.

Sag, strength and what the core does

Sag follows weight, tension, span and temperature together. Steel expands far less than aluminum when it heats, so an ACSR conductor holds its profile as current and ambient temperature rise, while an all-aluminum conductor of the same size sags further. That is the reason ACSR holds the long transmission spans and AAAC is common on distribution, where spans are shorter and tensions lower.

Strength per unit weight is the other half of the argument. The steel core gives ACSR the highest strength for its weight among the common bare conductors, which is what lets it be pulled to high tension between towers that are far apart. AAAC is stronger than plain all-aluminum conductor and lighter than ACSR at the same diameter, but its ultimate strength is generally lower for the same size.

Creep matters on anything that has been in service. Aluminum takes a permanent set under sustained tension, and conductor that has hung between two structures for years has already crept. It can still be reused, but it will not behave like new conductor on a new line, and a buyer will ask whether a reel is mill surplus or taken down.

Removed conductor is a different lot from mill surplus even when the construction matches. Anything pulled through sheaves, come-alongs and running boards carries the marks of it: kinks, birdcaging where the layers have opened, abrasion on the outer strands and flattened points under the clamps. A buyer looks at those before looking at the family, because they decide whether the conductor can be strung again.

Corrosion in coastal Georgia air

From Savannah and Brunswick down through Kings Bay and the islands, conductor lives in chloride-laden air, and the coastal belt stays humid for most of the year. In that environment the steel core is the weak point of ACSR. Moisture reaches the core through the gaps between strands, at cut ends, and under fittings. The steel rusts, the corrosion products take up more volume than the metal they replaced, and the aluminum layers can be forced apart from the inside.

Aluminum-clad and aluminized cores exist for this service, and they are what a coastal utility specifies. AAAC avoids the problem by having no couple: 6201 alloy resists atmospheric corrosion and there is no steel at the centre to rust. That is why AAAC and ACAR turn up on coastal distribution systems and in industrial atmospheres.

No bare conductor is immune to a bad yard. Aluminum corrodes under wet dirt, and a conductor stored on the ground, in standing water, or with an open cut end exposed to rain will show pitting that has nothing to do with its design. Storage condition and family matter about equally.

Telling them apart at a cut end

One cut end and a magnet answer it, and the answer can be photographed for someone else to check.

• Magnet on the core. ACSR holds a magnet at the centre of the cut. AAAC does not, and neither does ACAR.
• Core pattern. A 26/7 shows seven harder wires in the middle. A 19-strand AAAC is 1+6+12 with every wire the same size and temper.
• Knife test. A steel core wire will not shave. Alloy and aluminum will.
• Lustre. A galvanized core is dull grey against bright aluminum. An aluminum-clad core looks like aluminum, so rely on the magnet.
• Weight for the diameter. Measured against a published table, ACSR comes out heavier per foot because of the steel.
• Surface condition. White powdery corrosion between layers suggests moisture has been in the conductor, which matters more than the family.