The standard impedance boundary condition (SIBC) does not constitute an exact model of material coated perfect conductors with edges but may provide sufficient accuracy for engineering purposes. A numerical investigation of the SIBC accuracy is carried out for coated wedges and coated square cylinders for the case of transverse magnetic (TM) illumination. The numerical investigation reveals that although the SIBC model is less accurate for structures with edges than for planar structures, it remains applicable for a wide range of engineering problems. Hence, the TM far field from a large class of coated conductors with edges can be accurately predicted using the SIBC model.