A coupling (6) to attach an impeller (32) of a compressor to a shaft (16) of an electric motor. The coupling has a coupling body (100) that is attached at a first of the ends thereof to the impeller and at the opposite second end, to the motor shaft. The coupling body has a deformable section (106) between the first and second ends of the coupling body. The deformable section is configured such that under an unbalanced loading exerted against the coupling body upon a failure of the impeller, the deformable section will permanently deform without the ultimate strength of a material forming the coupling body being exceeded and prior to a permanent deformation of the shaft. In such manner, the electric motor is protected from damage upon a failure of the impeller.