The use of single-core sheathed cables for alternating currents

Abstract

It is frequently a matter of convenience to use single-core lead-covered cables for transmitting power by means of alternating current, and in such cases the magnitude of the loss arising from the eddy currents induced in the lead sheath becomes a matter of importance. Recently some power-supply authorities have refused to connect to their lines any distributing system depending upon the use of such cables.The eddy losses in the sheaths of these cables may be divided into two groups, called herein “sheath eddies,” and “sheath circuit eddies.” The latter occur only when one or more cables have their sheaths connected at more than one place.The losses are analysed for a single cable, a pair of single-phase cables, and a set of three-phase cables.It is shown that the sheath eddies are in all cases negligible, and that the sheath circuit eddies may be kept within reasonable limits by proper regulations regarding the spacing of the cables.It is suggested that the I.E.E. Wiring Rules should contain such regulations, and that so long as these are adhered to there is no justification for refusing to connect single-core lead-covered cables to any ordinary a.c. system. The necessary data are given for the framing of the regulations.Similar questions arise regarding armoured cables. The results in this case are awaiting the conclusion of the experiments now being carried on at the University of Birmingham.