In the described 480-VAC wall-mounted assembly, the main rating is 600 A and the branch rating is 125 A.

• A. 600 A main and 125 A branches
• B. 600 A main and 600 A branches
• C. 125 A main and 600 A branches
• D. None of the above

Answer: (A)

The main idea is that a panel’s main rating and its branch ratings serve two different protections. The main rating reflects how much current the panel and its main protective device can handle from the source—it's the upward limit for the entire assembly. The branch rating shows the maximum current that any single branch circuit within the panel is allowed to carry, which is determined by the size of the branch breakers and the conductors in those branches.

For this 480-VAC wall-mounted assembly, the main is rated to 600 A, so up to 600 A can flow into the panel before the main device trips. Each branch is rated for 125 A, meaning every individual branch circuit is protected or limited to 125 A. This keeps the wiring and devices in each branch within safe operating limits even though the overall panel can handle more current from the source.

Choosing 600 A main with 600 A branches would imply each branch could carry as much as the main, which isn’t the typical or safe configuration for such a panel. The option "None of the above" would be incorrect because the described combination matches the 600 A main and 125 A branches.