What is the key factor in determining the capacity for conduit with three or more cables?

The key factor in determining the capacity for conduit with three or more cables revolves around the filling and packing of these cables within the conduit to ensure they can be safely routed without overheating or becoming damaged. The correct choice provides a formula that incorporates both the diameter of the cables and their arrangement, specifically focusing on how much of the conduit’s internal space is being utilized.

The formula presented is based on the maximum allowable fill based on the National Electrical Code (NEC) standards, which generally stipulates that no more than 40% of the conduit’s internal area be filled when you have three or more conductors. This ensures adequate airflow and cooling, reducing the risk of the cables overheating during operation.

Using the square root of the sum of the squares of the diameters is a part of calculating the effective area that the cables occupy within the conduit. This approach is crucial as it not only considers individual cable sizes but also their number and arrangement, allowing for a comprehensive assessment of the conduit capacity.

Factors like cable length and the number of cables alone provide limited information compared to the nuanced understanding provided by this calculation, making it the most reliable method for ensuring compliance with safety and performance standards in conduit installation.