A GFCI will open a circuit if it senses an imbalance between supply and _______ current?

A GFCI, or Ground Fault Circuit Interrupter, is a critical safety device designed to prevent electrical shock by monitoring the flow of electricity in a circuit. It specifically detects any imbalances between the current coming into the circuit (supply current) and the current returning from it. If the GFCI senses that the return current is less than the supply current, it indicates that some current is likely escaping the circuit, which could potentially lead to a shock hazard.

This imbalance can occur if current is leaking through an unintended path, such as through a person's body into the ground. Upon detecting this imbalance, the GFCI quickly disconnects the power to prevent injury.

The other terms, such as bypass current, control current, and ground current, do not represent the correct concept in this context. Bypass and control currents are not standard terminology related to how GFCIs operate, and ground current, while related to overall earth grounding practices, does not specifically define the imbalance that the GFCI uses to determine when to trip the circuit. Thus, the reference to return current captures the essential function of GFCIs effectively.