Abstract: An electrical unit for plugging into a mount, in particular a self-contained emergency lighting unit, includes a hollow base the back of which plugs into a mount and has a back wall. It is removably closed at the front by at least one cover with, internally, at least one housing in which there is at least one active unit liable to be live. For fixing it to the hollow base, the cover is equipped with an elastically deformable lug which projects from its inside surface and the back wall of the hollow base has an opening for the elastically deformable lug of the cover to pass through and through which the latter is accessible from the rear of the hollow base, with at least one retaining lug on the hollow base for cooperating with it. Applications include self-contained emergency lighting units.