What are common symptoms that indicate a faulty circuit?

A common symptom that indicates a faulty circuit includes burnt odors and flickering lights. When there is a fault in the circuit, it can lead to excessive heat generation, which may cause insulation to deteriorate and components to overheat, thereby emitting burnt odors. Flickering lights are often a direct result of inconsistent power delivery, which can occur due to loose connections, overheating, or failing components within the circuit. Both symptoms signal underlying issues that need immediate investigation to prevent further damage or potential hazards.

In contrast, the other options indicate a lack of issues. Normal operation and consistent lighting suggest that the circuit is functioning properly and is free from faults. Frequent voltage changes without other signs may not always indicate a problem if the changes are within acceptable parameters, and high efficiency with low consumption is characteristic of a well-functioning circuit, further emphasizing that these do not point to faults.