What is the maximum area fill percentage for conductors, including splices and taps, in metal surface raceways?

The maximum area fill percentage for conductors in metal surface raceways is established to ensure safe operation and to avoid overheating caused by the accumulation of heat in confined spaces. The National Electrical Code (NEC) specifies that it is permissible to fill up to 75 percent of the conduit’s internal area with conductors. This percentage accounts for the physical space needed for splices and taps, which can take up additional area within the raceway.

When the fill exceeds this maximum, it can restrict airflow around the conductors, leading to increased temperature and potentially harmful conditions. Maintaining a fill percentage of 75 percent allows for both safe operation and efficient performance of the electrical system while ensuring compliance with safety regulations.

The other percentages provided do not align with the NEC requirements for metal surface raceways as they either under-represent the capacity that can safely be filled (like 50% or 60%) or exceed it (such as 90%), which could compromise safety due to overheating.