What does a Ground Fault Circuit Interrupter (GFCI) monitor?

A Ground Fault Circuit Interrupter (GFCI) is designed to monitor the amount of current flowing through the circuit, specifically the current between the hot and neutral wires. It continuously measures this current and will trip and cut off the electrical supply if it detects an imbalance, which indicates that some current is leaking to the ground. This can help prevent electric shocks or electrical fires due to ground faults, which are often caused by moisture, worn insulation, or other factors that could affect the safety of the circuit.

Understanding the other options provides additional context: the GFCI does not monitor voltage or temperature; these functions are more appropriate for circuit breakers or thermal overload devices. It also does not measure the frequency of electrical signals, as this is typically relevant in alternating current systems but not by GFCIs specifically. The crucial function of the GFCI centers around current discrepancies, highlighting its role in enhancing electrical safety.