What percentage of the branch-circuit rating can cord and plug connected appliances not exceed?

In residential wiring, the National Electrical Code (NEC) states that cord and plug connected appliances should not exceed 80 percent of the branch-circuit rating when calculating load. This limitation is implemented to prevent overheating and to ensure a safe operation of the electrical system.

The rationale behind this is that electrical circuits are typically rated for a certain maximum load capacity. By restricting the load to 80 percent of that capacity, it allows for additional safety margins and limits potential issues that may arise from overheating due to continuous use. Therefore, the safe practice for connecting appliances ensures that the circuit stays within safe operating limits, promoting electrical safety and efficiency.

The other options provide higher percentages that do not account for adequate safety precautions. Using 100 percent of the rating does not allow for any leeway in case of power surges or additional load, which can lead to circuit failure. Similarly, using 90 percent or 70 percent may not sufficiently cover the safety margin advised by industry standards.