What must the branch-circuit panelboard be sized to serve?

The correct answer emphasizes that the branch-circuit panelboard must be sized according to the calculated load, which is generally determined by volt-amperes per square foot basis for the intended application. This approach ensures that the panelboard can adequately handle the expected load, providing safe and reliable operation for the electrical system.

In practice, sizing the panelboard based on calculated load takes into consideration various factors, such as the type of occupancy, the expected usage of electrical devices, and any applicable demand factors outlined in the NEC. This ensures that the panelboard can accommodate all connected loads without risk of overloading, which can lead to hazards like overheating or electrical fires.

By considering the calculated load—rather than just aesthetic load, service load, or any additional load—the installation meets safety standards and operates efficiently, which is key to compliance with the National Electrical Code. This methodology protects both the electrical system and the facility it serves, ensuring long-term functionality and safety.