Conductor Requirements
Copper and aluminum are the most common conductor materials used in building
electrical wiring, although other materials can be used. As a general rule, solid copper
conductors are used in small conductor sizes (up to about 8 AWG) because safety issues
associated with aluminum are avoided and weight and cost are not significantly affected.
Medium- and large-gauge stranded aluminum cable (above No. 8 AWG) is safely used
on circuits as long as the terminals or connectors on the circuit are rated CU-AL (copper
aluminum) and an antioxidant paste is used on properly tightened connections.
Conductors are covered with insulation to provide electrical isolation and physical
protection of the conductor material. The type of insulation material determines the
environment in which a wire or cable can be used safely. Wires used indoors are
subjected to less exposure to the elements than those designed for outdoor use. Outdoor
wiring is exposed to water and sunlight, so the insulation is designed to withstand these
elements. Insulation on wires buried in the ground must also be able to withstand the
damp, corrosive environment of the soil. Insulation used to cover electrical conductors
are designated with a set of letters that describes the properties of the insulation.
