What is the maximum percentage of a branch circuit rating that can be used for permanently installed equipment when also supplying cord-and-plug connected equipment?

The correct choice is based on the National Electrical Code (NEC) guidelines regarding branch circuit ratings and their application to permanently installed equipment along with cord-and-plug connected equipment. When a branch circuit supplies both permanently installed equipment and cord-and-plug connected equipment, the NEC permits up to 50 percent of the branch circuit's maximum rating to be used for the continuation of the permanently installed loads.

This percentage helps ensure that the circuit is not overloaded when both types of loads are in use simultaneously. The regulation recognizes that cord-and-plug connected equipment typically has a variable usage, while permanently installed equipment tends to have a more constant demand. Therefore, allowing the use of up to half of the branch circuit's capacity ensures safe operation without exceeding the circuit's rating.

Understanding this context is critical for ensuring that installations remain within safe operational thresholds, assisting electricians in compliant system design. This mainstream practice reinforces safety and efficiency when planning electrical systems.