Overhead lines carry most of the distribution grid, and the choice of conductor is a trade-off between required current, span length and environment. Three bare aluminium conductors cover most applications, alongside a covered option increasingly used on difficult routes.
| Type | What it is | Strong point | Weak point |
|---|---|---|---|
| AAC | All-aluminium conductor, high-purity aluminium strands | Best conductivity for its weight, good corrosion resistance | Low tensile strength, short spans only |
| AAAC | All-aluminium-alloy conductor (6201 type alloy) | Better strength-to-weight and sag than AAC, fully aluminium so corrodes little | Slightly lower conductivity than pure aluminium |
| ACSR | Aluminium conductor, steel reinforced | Highest strength, longest spans, river crossings | Steel core can corrode; heavier |
The selection logic is straightforward. AAC suits short urban spans where poles are close and mechanical load is low. AAAC occupies the middle ground, and its better sag behaviour makes it well suited to coastal and industrial areas that need extra strength without a corrodible steel core. ACSR handles long spans and heavy loading, because the galvanised steel core carries the mechanical tension while the aluminium carries the current.
All three bare types share one limitation: brief contact with a branch, a bird or an illegal hook can short the line or permit theft. A covered conductor encloses the aluminium in an insulating layer, so incidental contact no longer trips the feeder or risks a fire, which is the principal reason for using it on tree-lined and theft-prone routes. See APAR covered conductors (MVCC) for the 11 kV to 132 kV range, and aerial bunched cables where a bundled LV overhead system is more appropriate than open wires. The conductor should be matched to the span and the surroundings; the least expensive conductor is rarely the least expensive line over its service life.