Which of the following is NOT a circuit fault?

A closed circuit refers to a complete electrical path where current can flow freely. In the context of circuit faults, a closed circuit is actually the desired state for operation; it indicates that a circuit is functioning properly.

In contrast, open, shorted, and grounded circuits represent fault conditions. An open circuit means there is a break in the path, preventing current from flowing. A shorted circuit occurs when a low-resistance connection forms between two points, which can create excess current flow and potentially damage components. A grounded circuit can refer to an unintended path between a current-carrying conductor and the ground, which can also create unsafe conditions and malfunctions.

Thus, identifying a closed circuit as not being a fault is rooted in the understanding that it signifies normal operation, while the others are indicative of problems within the circuit.