1. A microcontroller-based system for automatically measuring a load current via a ground fault sensing transformer in a circuit to which a load is connected, comprising: a resonant circuit that includes a current transformer through which at least two load conductors connected to the load pass, the current transformer having a ferrite core and a secondary winding, the resonant circuit including an output signal responsive to current flow in the load conductors; and a microcontroller operatively coupled to the resonant circuit, the microcontroller being programmed to automatically determine a load current consumed by the load by calculating a resistive core loss associated with the ferrite core and a function that includes a value based on the resistive core loss.