Which of the following is NOT a cause of electrical circuit fires?

Understanding the causes of electrical circuit fires is crucial for ensuring safety on board. Open flames do not inherently cause electrical circuit fires; instead, they may be a result of igniting other flammable materials that are not directly related to the electrical system.

The other causes listed—poor wiring, worn insulation, and overloading—directly relate to electrical components and their functionalities. Poor wiring can lead to shorts or exposed wires, which can ignite surrounding materials. Worn insulation allows electrical currents to escape, posing a fire hazard. Overloading occurs when too much current flows through a circuit, generating excess heat that can spark a fire. Thus, while open flames can result in fires, they do not directly cause electrical circuit fires in the same manner or context as the other options presented.