Electric current metal (ideal) resistor (or other ohmic device): where formula_6 is the current, measured in amperes; formula_26 is the potential difference, measured in volts; and formula_27 is the resistance, measured in ohms. For alternating currents, especially at higher frequencies, skin effect causes the current to spread unevenly across the conductor cross-section, with higher density near the surface, thus increasing the apparent resistance. The mobile charged particles within a conductor move constantly in random directions, like the particles of a gas. (More accurately, a Fermi gas.) To create a net flow of charge, the particles must also move together with an average
Aluminium-conductor steel-reinforced cable rise due to the inverse relationship between resistance and conductor cross sectional area. The skin effect benefits the design, as it causes the current to be concentrated towards the low-resistivity aluminum on the outside of the conductor. To illustrate the impact of the skin effect, the American Society for Testing and Materials (ASTM) standard includes the conductivity of the steel core when calculating the DC and AC resistance of the conductor, but the (IEC) and The CSA Group standards do not. In a conductor (ACSR and other types) carrying AC current, if currents are flowing through one or more other