This report deals with an investigation of eddy-current losses in multi-core circular-conductor and shaped-conductor paper-insulated wire-armoured cables, and the development of formulae by means of which the losses can be computed. The experimental work covers tests with balanced three-phase currents at frequencies from 25 to 300 cycles per second.The eddy-current losses are divided into four parts, namely, skin effect, proximity effect, lead-sheath effect, and armouring effect. The ratio of a.c. to d.c. resistance of the conductors, calculated by the appropriate formula, is, with one exception, within 5% of the measured value under all the conditions covered by the investigation, the average difference between calculation and measurement being only 1%.