A transformer for current supply and/or signalling purposes, in particular for use in a connector arrangement for electrical circuits in underwater installations, includes a magnet circuit, a first winding having a plurality of turns and a second winding having one or very few turns, whereby turn portions of both windings pass essentially in parallel through one or more openings in the magnetic circuit. For obtaining advantageous electrical properties, turn portions of the first winding are so arranged that along a major part of their length which is surrounded by the magnetic circuit they are individually enclosed by that or those conductors which constitute the turn portions of the second winding that are surrounded by the magnetic circuit.