Which ground fault detection method involves sensing current in only one conductor?

The method of ground fault detection that involves sensing current in only one conductor is the residual sensor. This type of sensor measures the current flowing through the single conductor and, in doing so, can determine if there is a ground fault present by comparing the current in that conductor to the return path, which is typically grounded. If there is a discrepancy between the current moving out through the conductor and the current returning, it signals that some current is leaking to ground, indicating a fault.

The residual sensor is particularly effective for identifying ground faults in systems where an imbalance in current flow can be indicative of an unsafe condition. This method is essential in protecting electrical systems by providing timely detection of faults that could lead to electrical shocks or fires.

In contrast, grounding electrode systems, differential sensors, and current transformers either do not focus solely on one conductor or utilize different methodologies that involve multiple conductors or a more complex analysis of current flow. Therefore, the unique capability of the residual sensor to detect imbalances based solely on one conductor makes it the correct choice for this question.