What is the maximum sum of cross-sectional areas of all conductors and cables at any cross-section of a non-metallic wireway?

The maximum sum of the cross-sectional areas of all conductors and cables in a non-metallic wireway is specified as 20% of the cross-sectional area of the wireway. This percentage ensures that there is adequate space for air circulation and the prevention of overheating, which could occur if conductors are packed too tightly. The 20% limit is a common practice in electrical installation codes and guidelines, helping to maintain safety and compliance in electrical installations.

This choice reflects considerations of thermal management and physical space within the wireway, ensuring that the conductors can operate effectively without risks associated with overcrowding. Lower percentage limits, like 10% or 15%, would be insufficient for typical installations, while a higher limit, such as 25%, could compromise electrical safety standards and heat dissipation capabilities. Therefore, adhering to the specified maximum of 20% allows for safe and efficient operation of the wireway while accommodating necessary electrical conductors.