A leakage current protection device with a single laminated magnetic core transformer that is formed by punch pressing an amorphous metal material, or a nanocrystalline soft metal material, in a high punch velocity press to form the ring laminations for the magnetic core. In a ground fault circuit interrupter, the single laminated magnetic core transformer serves as the input sensor for both the current imbalance detection circuitry and the low impedance ground fault protection circuitry.