What percentage of the interior cross-sectional area of the underfloor raceway can the combined cross-sectional area of all conductors or cables not exceed?

The correct percentage for the combined cross-sectional area of all conductors or cables in an underfloor raceway is 40%. This requirement is established to ensure that there is sufficient space within the raceway for proper heat dissipation, accessibility for installation and adjustments, and to maintain the integrity of the electrical installation. By limiting the fill percentage, the risk of overheating and related safety hazards can be minimized.

In practice, keeping the conductor fill at or below this specified limit helps to ensure compliance with electrical codes, which prioritize safety and effective performance in electrical installations. Thus, the answer highlighting 40% reflects the regulatory standards designed to provide safe and efficient operation of electrical systems.