function is to establish the passage of multiphase currents to a load such as a motor and a thermal relay 3 whose function is to react to low but extended current overloads contactor 2 is fixed to a profiled rail 4 which is fixed to a wall or plate such as 5 the contactor has a first set of power switches whose input terminals and output terminals are shown by the references 6 7 8 respectively 9 0 11 a second set of signaling switches possibly only comprising one as can be seen in fig1 has an input terminal 13 and an output terminal 14 the case 12 of the contactor has under its base 15 a recess 16 which is limited by a fixed edge 17 and which receives on the opposite side the end 18 of a resiliently mobile hook or latch 20 see fig2 this end and this edge are engaged on the flanges 21 22 of the profiled rail 4 as can be seen in fig1 this locking hook 20 has a projecting lug 23 and an operating eye or notch 24 which are laterally offset with respect to a plane of symmetry pp 39 of the contactor this offset.