An electrical coupling unit having: an electrical connector for push-fit electrical connection in an axial direction of the coupling unit to a mating electrical connector of a receiving unit, the electrical connector and the mating electrical connector having respective engagement formations (22, 22') which permit the push-fit connection only when the electrical connector is in a predetermined rotational alignment about the axial direction with the mating electrical connector; a backshell in a fixed rotational relationship with the electrical connector and extending rearwardly therefrom to house, in use, one or more electrical leads extending rearwardly from the electrical connector; and a coaxial actuation sleeve surrounding the backshell, the actuation sleeve being axially movable to effect the push-fit connection; wherein the backshell and the actuation sleeve are operatively connected such that: movement of the actuation sleeve in a forward axial direction towards the receiving unit is resisted by contact of the electrical connector with the mating electrical connector to produce rotation of the backshell, thereby rotationally aligning the electrical connector with the mating electrical connector and allowing push-fit electrical connection of the electrical connector to the mating electrical connector; and characterised in that the backshell and the actuation sleeve are operatively connected by one or more cam formations which, on contact of the electrical connector with the mating electrical connector, convert forward axial movement of the actuation sleeve into the rotation of the backshell. an electrical connector for push-fit electrical connection in an axial direction of the coupling unit to a mating electrical connector of a receiving unit, the electrical connector and the mating electrical connector having respective engagement formations (22, 22') which permit the push-fit connection only when the electrical connector is in a predetermined rotational alignment about the axial direction with the mating electrical connector; a backshell in a fixed rotational relationship with the electrical connector and extending rearwardly therefrom to house, in use, one or more electrical leads extending rearwardly from the electrical connector; and a coaxial actuation sleeve surrounding the backshell, the actuation sleeve being axially movable to effect the push-fit connection; wherein the backshell and the actuation sleeve are operatively connected such that: movement of the actuation sleeve in a forward axial direction towards the receiving unit is resisted by contact of the electrical connector with the mating electrical connector to produce rotation of the backshell, thereby rotationally aligning the electrical connector with the mating electrical connector and allowing push-fit electrical connection of the electrical connector to the mating electrical connector; and characterised in that the backshell and the actuation sleeve are operatively connected by one or more cam formations which, on contact of the electrical connector with the mating electrical connector, convert forward axial movement of the actuation sleeve into the rotation of the backshell.