Final answer:
The safe current rating for a portable appliance on a 30-amp branch circuit is 24 amps, calculated as 80% of the circuit's capacity due to safety regulations.
Step-by-step explanation:
The maximum permitted current rating of a portable appliance on a 30-ampere branch circuit is 24 amps. This is based on safety regulations that limit continuous use to 80% of the circuit breaker's capacity to prevent potential damage from large currents and to ensure safe operation. Since circuit breakers are designed to protect against overcurrent by interrupting the flow of electricity, adhering to this 80% rule is crucial for the protection of electrical appliances and preventing electrical hazards.