Copper Conductors
Copper conductors are what the electric industry used when we started building the grid in the late 1800s and it saw continued use through the mid 1900s. These copper conductors are strong, highly conductive and they were readily available during that time period. Although copper has some superior qualities, it is also heavy which causes it to have increased sag and larger structures to carry the weight. Copper also is limited to a maximum operating temperature of 80°C (176°F) before it begins to anneal and loose strength. Copper wires have a high salvage value and can often significantly offset the cost to reconductor lines.
Aluminum Conductors
All Aluminum Conductors (AAC) were used as early as the 1830s due to their low weight, but they lack the strength of other conductors and could not be used for longer spans. In the late 1960s, other alloying elements were added to the aluminum to make it stronger to make All Aluminum Alloy Conductors (AAAC). These were stronger than their predecessors but still had limited use in transmission length spans. Both AAC and AAAC begin to anneal at 93°C (199°F) and loose strength, so most utilities limit their maximum operating temperature to 93°C (199°F) - 100°C (212°F). Aluminum wires have a modest salvage value and can offset some of the cost to reconductor lines.
Steel Core Conductors
In 1908, a revolutionary change happened when steel strands were added to the core of the aluminum conductors to improve their strength. These new conductors were called Aluminum Conductors Steel Reinforced (ACSR), and this change allowed utility companies to have longer spans and fewer structures. Approximately 80% of the conductor strength comes from the steel core and the remaining strength comes from aluminum. The aluminum begins to anneal at 93°C (199°F) and looses strength, so most utilities limit their maximum operating temperature to 93°C (199°F) - 100°C (212°F). In the early 1970s, fully annealed aluminum strands were added to these conductors, and Aluminum Conductors Steel Supported (ACSS) was created. Since these strands were now fully annealed, the steel core carries 100% of the tension and the conductor can operate at temperatures as high as 250°C (482°F). These conductors can carry more current than their ACSR counterparts, but suffer from lower tension limits and increased sag.