What device stops electricity flow when current-to-ground exceeds a predetermined value?

The correct answer is the Ground Fault Circuit Interrupter (GFCI) or Residual Current Device (RCD). This device is specifically designed to protect people from electrical shock by monitoring the current flowing through an electrical circuit. It functions by detecting any imbalance or leakage of current between the live and neutral wires, which can occur if there is a fault in the wiring or if someone comes into contact with a live wire. When a ground fault is detected, such as when the current flowing to the ground exceeds a predetermined threshold, the GFCI or RCD quickly interrupts the electrical circuit, effectively stopping the flow of electricity and reducing the risk of serious injury or death from electric shock.

In contrast, a circuit breaker serves to prevent overloads and short circuits by tripping when the current exceeds a safe level but does not specifically monitor for ground faults. A fuse also interrupts the circuit but relies on melting a wire when the current exceeds a set threshold, without the advanced sensing capabilities of a GFCI or RCD. A voltage regulator, meanwhile, is designed to maintain a constant voltage level and does not protect against ground faults at all.