<p>The actuated nonlinear beam model is widely used in the analysis of both static and dynamic pull-in in micro- and nanostructures. Conventional approaches typically utilize a simplified model that neglects axial inertia. However, assessing the impact of this factor on the nonlinear beam dynamics and dynamic pull-in is of significant interest. This paper is devoted to determining the limits of applicability for such simplifications, with primary focus directed toward the pull-in phenomenon. An analytical and numerical investigation into the influence of axial inertia on pull-in values is performed. Based on nonlinear mathematical models and numerical algorithms previously developed by the authors, an asymptotic simplification of the nonlinear beam vibrations is conducted. Both the zeroth- and first-order approximations of the initial-boundary value problem are considered. Their leading terms allow accounting for axial inertia in an approximate form. A small parameter for the asymptotic expansion is defined as the reduced ratio of the plate bending stiffness to its tensile/compressive stiffness. It is demonstrated that pull-in occurs at relatively small displacements, where the influence of higher-order nonlinear terms in the curvature and strain expressions remains marginal. The accuracy of the proposed model and numerical algorithm is validated against experimental data. The results of this study establish that for plates of standard dimensions under typical operating conditions, the effect of axial inertia is negligible, and the simplified model is well-justified for practically relevant scenarios.</p>