Which condition can lead to thermal overload in electrical systems?

Thermal overload in electrical systems occurs when excessive current flows through the conductors, which generates heat due to the resistance of the material. When the current exceeds the rated capacity of the equipment or conductors, it results in an increase in temperature that can compromise the integrity of insulation and other components, potentially leading to failure or hazardous conditions. This condition is critical to monitor and manage in electrical systems to prevent overheating and ensure safe operation.

The other conditions described, such as lower than normal current, increased resistance, or low operational voltage, do not directly contribute to thermal overload. Lower than normal current would actually reduce the likelihood of overheating. Increased resistance tends to limit the current flow, preventing heat accumulation. Low operational voltage could lead to inadequate power levels but does not contribute to thermal overload in the way excessive current does.