Abstract: The fixing device for fixing onto a symmetrical rail comprises a fastening piece and a blade spring. The fastening piece includes a body having first and second hooks, with a third hook between them. The fastening piece also includes a rod connected to the body by a connection zone including a tooth. The blade spring has a longitudinal slot, a first bridge at one end of a curved part and a second bridge at an arched end of the blade spring; these bridges cooperate with the tooth and the third hook to fix the blade spring. The fastening piece is fixed to a case having an earthing terminal fixed to the rod on the fastening piece thereby providing an earth connection for the rail.