The standard return for electrical and electronic circuits is the earth ground. When an electrical or electronic device fails, it may open the return circuit to the earth ground.
DC powers battery operated vehicles and other machines and electronics. Converters can change AC to DC and vice versa. High-voltage direct current transmission uses big converters. That’s it an electrical curcit.
When an open circuit to earth ground is detected, the G.F.I. device immediately opens the voltage source to the device. G.F.I. devices are similar to circuit breakers but are designed to protect humans rather than circuit components.
Electrical and electronic circuits can be complicated. Making a drawing of the connections to all the component parts in the circuits load makes it easier to understand how circuit components are connected.