Explain the operation of a 'ground fault interrupter' (GFI) and its role in electrical safety.

A Ground Fault Interrupter (GFI), also known as a Residual Current Device (RCD), is a safety device designed to quickly interrupt an electrical circuit when it detects a ground fault, which is an unintended path of current flow to ground. Its primary role in electrical safety is to protect people from electric shock. A GFI works by monitoring the current balance between the supply conductor (hot wire) and the return conductor (neutral wire) of a circuit. Under normal operating conditions, the current flowing through the hot wire should be equal to the current flowing back through the neutral wire. If a ground fault occurs, some of the current will flow through an unintended path to ground, such as through a person touching a live wire. This creates an imbalance between the hot and neutral currents. The GFI detects this imbalance and quickly interrupts the circuit, typically within milliseconds, preventing a sustained and potentially lethal electric shock. The GFI uses a differential transformer to monitor the current balance. The hot and neutral wires pass through the transformer, and if there is a current imbalance, a voltage is induced in the transformer's secondary winding. This voltage triggers a circuit breaker to trip, interrupting the power supply. GFIs are commonly used in areas where there is a high risk of electric shock, such as bathrooms, kitchens, and outdoor locations. They are an essential safety device for protecting people from the hazards of electrical current.