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If heat is produced at a sufficient rate, the conductor temperature rises and the insulation can be damaged or ultimately the conductor itself can sag or melt. The ampacity rating for a conductor is based on the conductor diameter, material used (copper or aluminum), the rated maximum application temperature, and the installation conditions.
Aluminium conductor steel-reinforced cable (ACSR) is a type of high-capacity, high-strength stranded conductor typically used in overhead power lines. The outer strands are high-purity aluminium, chosen for its good conductivity, low weight, low cost, resistance to corrosion and decent mechanical stress resistance.
Its light weight and softness result in roughly 30% greater conductivity than an equivalent ACSR conductor, allowing 14% more current to be carried at equal temperature. For example, 1.107 in (28.1 mm) diameter ACCC "Drake" conductor at 75 °C has an AC resistance of 106 mΩ/mile, [ 7 ] while equivalent ACSR conductor has an AC resistance of ...
Similarly, if two conductors are near each other carrying AC current, their resistances increase due to the proximity effect. At commercial power frequency, these effects are significant for large conductors carrying large currents, such as busbars in an electrical substation, [2] or large power cables carrying more than a few hundred amperes.
An additional wire, called the bond (or earth) wire, is often connected between non-current-carrying metal enclosures and earth ground. This conductor provides protection from electric shock due to accidental contact of circuit conductors with the metal chassis of portable appliances and tools.
In electrical engineering, Neher–McGrath is a method of estimating the steady-state temperature of electrical power cables for some commonly encountered configurations. By estimating the temperature of the cables, the safe long-term current-carrying capacity of the cables can be calculated.
The carbon core conductor's reduced thermal sag allows it to carry up to twice the current ("ampacity") compared to all-aluminum conductor (AAC) or ACSR. The power lines and their surroundings must be maintained by linemen , sometimes assisted by helicopters with pressure washers or circular saws which may work three times faster.
Comparison of SWG (red), AWG (blue) and IEC 60228 (black) wire gauge sizes from 0.03 to 200 mm² to scale on a 1 mm grid – in the SVG file, hover over a size to highlight it. In engineering applications, it is often most convenient to describe a wire in terms of its cross-section area, rather than its diameter, because the cross section is directly proportional to its strength and weight ...