The method of volume averaging is used to examine the form of Maxwell's equations in two-phase systems. The volume averaged equations for the individual phases are developed and used to identify the condition of local electrodynamic equilibrium. When this condition is satisfied, the electric and magnetic fields in the two phases are close enough so that single equations can be used to describe these fields. The one-equation model for the electric and magnetic fields is obtained without the need for closure problems; however, the constraints associated with the principle of local electrodynamic equilibrium are very severe and are not satisfied for many processes.