This paper presents a brief theoretical discussion on the issue of the wire-grid representation of surfaces using the Numerical Electromagnetics Code (NEC). Different approaches for the determination of the parameters (in particular, the segment radii) of a wire-grid representation of a metallic surface are presented. These approaches are tested vs experimental data on electric field distribution inside a Transvers Electro-Magnetic (TEM) cell. The obtained data are compared to simulation results showing reasonable agreement for models featuring rectangular meshes.