The alternating-current resistance of hollow, square conductors

An approximate formula for the alternating-current resistance of isolated, hollow, square conductors, including the solid conductor as a special case, is developed theoretically. Experimental results are given to show that this formula is correct to within about 2 % at all frequencies. Formulae for the proximity effects in single-phase and 3-phase systems are also developed. These formulae are based partly on theoretical development and partly on experimental results. The experimental results cover most of the values likely to be encountered in practice.