An earthing brush assembly including an earthing brush and a brush mounting plate configured to radially and axially retain the brush, the brush having a support and a plurality of conductive individual fibres mounted in the support, the mounting plate providing a radial main body axially delimited by a first front face and by a second front face, and a plurality of tongues for axially and radially retaining the brush, the tongues being circumferentially distributed around the main body of the mounting plate and extending axially from the second front face of the main body. The brush mounting plate includes at least three mounting segments extending radially outwards from an outer surface of the main body, the mounting segments being distributed circumferentially around the main body of the mounting plate, each one of the segments locally surrounding the support of the earthing brush while remaining radially separated from the support.