is arranged on a bearing bush 23 respectively of the square sleeves 19 its control tracks 24 actuate a longitudinally moved control rod 27 acting on electrical switches 26 the supply of current to the electric motor 3 or 4 is switched off by switches 26 if the toothed segment 16 is located in its end positions determined by the stops 17 this end disconnection of the electric motors 3 and 4 is accessible from outside by using the clamp rings 25 when the adjusting device 1 is in its assembled state without its insulating protective casing 2 having to be opened for this the worm gear 13 in engagement with the drive worm 12 of the electric motor 3 or 4 respectively the thrust plate 14 forming a slip coupling therewith and its pinions 15 are provided with an axle 28 which may be displaced longitudinally in the gear frame 22 said axle passing through the gear wheel 13 which is mounted unchangeably in its position by a stop 29 so that the axle is freely movable a spring fixed to the gear frame 22 and pressing towards the worm gear 13 is located at its end taken up by the clutch plate 14.