Which of the following must not enter the service raceway or equipment where overhead service conductors are arranged?

The primary concern with overhead service conductors is the integrity and safety of the electrical system. Water must not enter the service raceway or equipment because it can lead to dangerous conditions, including short circuits, corrosion, and potential electrocution. Water can bridge electrical connections and create unexpected paths for current, which raises significant safety hazards.

Dirt, air, and insects, while they can present concerns in certain situations, do not inherently carry the same level of immediate risk to electrical systems. For instance, dirt may accumulate but can be managed and is less likely to cause a direct electrical failure compared to water. Air is essential for ventilation and does not pose a risk in terms of electrical conductivity or causing shorts. Insects, while they can occasionally cause issues, typically do not lead to the same immediate and hazardous conditions as water can. Understanding this distinction is critical for ensuring safe electrical installations, especially in areas exposed to the elements.