The invention relates to a cable harness output adaptor (5) for a cable tray including two semi-cylindrical half-shells (5A, 5B) made of plastic material, assembled in a complementary manner to form a cylindrical piece extending along at least one longitudinal axis (X′X) and defining two cylindrical parts (P1, P2): a first cylindrical part (P1) for internal cable harness support (3) and for externally receiving at least one clamping collar for the assembled half-shells (5A, 5B), and a second, cylindrical output part (P2) with external grip (20) of at least one protective sheath of the cable harness.