In an alternating current pipe-type cable system in which a group of individual insulated conductors are loosely disposed eccentrically within a conduit, an electromagnetic field shaping device interposed between the conductors and the conduit wall, so as to line the wall is configured so as to reduce eddy current losses in the conduit and in the conductors. The device is in the form of a slotted cylinder positioned so that the slot is diametrically opposite the group of conductors thereby to redistribute the magnetic flux induced. The device is preferably laminated in the radial and axial directions.