What does a GFCI device do when it detects current to ground exceeds acceptable values?

A Ground Fault Circuit Interrupter (GFCI) device is designed to protect against electrical shock caused by ground faults, which occur when electricity flows through an unintended path to the ground. When a GFCI detects that the current flowing to the ground exceeds a preset threshold—indicating a potential fault—it acts quickly to enhance safety by disconnecting the circuit.

This rapid disconnection of ungrounded conductors reduces the risk of electric shock or fire by interrupting the flow of electricity in the event of a ground fault. The GFCI continuously monitors the current balance between the incoming and outgoing currents; if there is an imbalance—often caused by leakage currents to ground—the GFCI will open the circuit.

The other options relate to different functions and capabilities that a GFCI does not possess. For example, increasing circuit capacity and blocking incoming current are not applicable to the operation of GFCIs, as their primary function is to interrupt flow rather than to manage supply or load. Switching to backup power is also outside the scope of a GFCI's purpose, which focuses solely on providing protection from electrical hazards related to ground faults.