What is an open circuit fault and how would you locate it using a wiring diagram?

• A. An open circuit is a short to ground; locate by tracing from the load toward the source.
• B. An open circuit is a break preventing current flow; locate by tracing from the power source toward the load on the diagram and performing continuity checks.
• C. An open circuit is a high resistance path that prevents any current flow at all times; locate by resistance measurement.
• D. An open circuit is a fault that creates a closed loop; locate by visual inspection only.

Answer: (B)

An open circuit fault means there’s a break somewhere in the conductor or a connection that prevents current from flowing along the path. Because the path is interrupted, no current reaches the load even though the source may be energizing other parts of the circuit.

To locate it on a wiring diagram, follow the actual current path from the power source toward the load, tracing each segment and connection that should be continuous. Use a continuity check along that path—with the circuit safely de-energized—by testing between adjacent points or nodes. Where continuity is lost (the meter shows no continuity or a very high resistance), you’ve found the open. The diagram helps you know which pieces should be connected in sequence and where the break is likely located.