The unified symmetry of mechanico-electrical systems with nonholonomic constraints of non-Chetaev’s type are studied, and the definition and the criterion of unified symmetry of mechanico-electrical systems are deduced from the Lagrange-Maxwell equations. The Noether conserved quantity, the Hojman conserved quantity and a new conserved quantity deduced from the unified symmetry are obtained. An example is given to illustrate the application of the results.