A ground wire provides a conducting path to the earth which is separate and independent from the path of an electrical appliance. Also, a ground wire is an additional pathway for an electric current to safely return to the ground without imposing danger to anyone in the event that a short circuit might occur. This is particularly important for shock hazard since it forces the breaker to trip by supplying a path to the ground if ever a hot wire comes in contact with a metal case of the appliance.
A fuses and circuit breakers limit the current which can possibly flow in a circuit. The metal filament present in the fuse will melt and break the connection. On the other hand, the circuit breaker with its bimetallic strip's heating effect causes a bending and tripping of a spring-loaded switch.
