Pole-top fires can occur when moisture in the air combines with dust and dirt built up on power lines or insulators (used to attach lines to wooden poles) and creates a path by which electricity can travel from lines to the wooden pole or cross arm they are attached to. This is known as "tracking."
When this happens, the pole or cross arm can heat up and catch fire. The fire damage or the resulting short circuit can cause an outage, as poles damaged by fire usually need to be replaced, or the line may need to be repaired. Drought and humid weather (without rain) contribute to the risk of pole top fires, and fog, light rain, or light, wet snow can provide the right conditions for pole-top fires to occur. Insulators damaged by lightning or other issues may also cause a pole fire.