An experimental investigation of the eddy-current losses in cables when carrying alternating current at power frequencies has been carried out at the National Physical Laboratory. Measurements were made with single-phase current on two parallel cables of equal length, and of 1.4 sq. in. conductor section, forming “go and return”.Formulae are put forward for estimating the a.c. resistance of a cable from the design data, and these formulae are shown to give good agreement with the experimental figures.