  The most general electrodynamic equations of a perfect conducting state are
obtained using a variational principle in a classical framework, following an
approach by Pierre-Gilles de Gennes. London equations are derived as the
time-independent case of these equations, corresponding to the magnetostatic
minimal energy state of the perfect conducting system. For further
confirmation, the same equations are also derived in the classical limit of the
Coleman-Weinberg model, the most successful quantum macroscopic theory of
superconductivity. The magnetic field expulsion is, therefore, a direct
consequence of zero resistivity and not an exclusive property of
superconductors.
