What is the permitted cross-sectional area fill for a 4" x 4" metal wireway?

To determine the permitted cross-sectional area fill for a 4" x 4" metal wireway, you need to understand the concept of fill capacity as outlined in electrical codes and standards. A metal wireway is typically designed to manage and protect electrical conductors, and the fill capacity is essential for safety and functionality.

A 4" x 4" wireway has a total cross-sectional area of 16 square inches. However, the National Electrical Code (NEC) specifies the maximum allowable fill for wireways to prevent overheating and ensure safe operation. This is generally calculated by taking a percentage of the total area, considering factors like the types of conductors and their insulation types.

The calculation for fill allows a maximum of 20% occupancy by conductors, but some specific guidance may adjust this percentage depending on factors like cable insulation and types. Given that 20% of the total area would result in a maximum fill of 3.2 square inches, the correct answer represents the maximum cross-sectional area that would be safely permitted without exceeding this occupancy limit.

Therefore, 3.2 square inches is the maximum fill that permits safe thermal and mechanical conditions within the wireway, making it the right answer.