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

The correct answer, which identifies the maximum sum of cross-sectional areas of all conductors and cables at any cross-section of a non-metallic wireway, reflects standard guidelines established for safe and effective wiring practices.

The rationale for selecting 20% is based on the principle that in non-metallic wireways, the total area occupied by conductors should not exceed a certain threshold to ensure proper heat dissipation and prevent overheating. Cable and conductor installations must allow for adequate spacing and airflow to maintain the integrity and performance of the electrical system.

In this instance, maintaining the total cross-sectional area of the conductors at 20% of the wireway's total cross-sectional area is essential for promoting safety and reliability. It mitigates the risk of overheating that can occur if too many conductors are crammed into a confined space, leading to a potential failure of the electrical system. This limit helps uphold both code compliance and best practices in electrical installations.