A hanger for an overhead railway line adapted to be fixed between a carrying cable or a bracket and a power supply contact wire, comprising: a clamp to tighten an undercut portion of the contact wire, and a negative-stiffness elastic device connected to the clamp, the elastic device comprising: an elastic element, a spacer to connect the clamp to the elastic element under traction/compression; a calibrated friction action; characterized in that the elastic device further comprises a pre-compressed elastic assembly along a first direction and having a movable point to shift in a second direction transverse to the first direction so as to decrease the pre-compression following a load disturbance; and in that the elastic element is connected to the pre-compressed elastic assembly to apply, in the second direction, an action onto the movable point when the clamp is moved upon the passage of a pantograph on the contact wire; the calibrated friction action being generated upon the movement of the movable point; and the negative-stiffness elastic device being configured so that the movable point has a neutral position when the hanger is fixed to the overhead line and the contact wire is still, and so that the clamp, acting on the elastic element by means of the spacer, brings the movable point back to the neutral position due to the longitudinal tension of the contact wire after the passage of the pantograph, the movable point moving along the second direction to release elastic energy of the elastic assembly when the passage of the pantograph occurs. a clamp to tighten an undercut portion of the contact wire, and a negative-stiffness elastic device connected to the clamp, the elastic device comprising: an elastic element, a spacer to connect the clamp to the elastic element under traction/compression; a calibrated friction action; characterized in that the elastic device further comprises a pre-compressed elastic assembly along a first direction and having a movable point to shift in a second direction transverse to the first direction so as to decrease the pre-compression following a load disturbance; and in that the elastic element is connected to the pre-compressed elastic assembly to apply, in the second direction, an action onto the movable point when the clamp is moved upon the passage of a pantograph on the contact wire; the calibrated friction action being generated upon the movement of the movable point; and the negative-stiffness elastic device being configured so that the movable point has a neutral position when the hanger is fixed to the overhead line and the contact wire is still, and so that the clamp, acting on the elastic element by means of the spacer, brings the movable point back to the neutral position due to the longitudinal tension of the contact wire after the passage of the pantograph, the movable point moving along the second direction to release elastic energy of the elastic assembly when the passage of the pantograph occurs. an elastic element, a spacer to connect the clamp to the elastic element under traction/compression; a calibrated friction action; characterized in that the elastic device further comprises a pre-compressed elastic assembly along a first direction and having a movable point to shift in a second direction transverse to the first direction so as to decrease the pre-compression following a load disturbance; and in that the elastic element is connected to the pre-compressed elastic assembly to apply, in the second direction, an action onto the movable point when the clamp is moved upon the passage of a pantograph on the contact wire; the calibrated friction action being generated upon the movement of the movable point; and the negative-stiffness elastic device being configured so that the movable point has a neutral position when the hanger is fixed to the overhead line and the contact wire is still, and so that the clamp, acting on the elastic element by means of the spacer, brings the movable point back to the neutral position due to the longitudinal tension of the contact wire after the passage of the pantograph, the movable point moving along the second direction to release elastic energy of the elastic assembly when the passage of the pantograph occurs.