Per 404.14(A), an alternating-current general-use snap switch used to supply a one-horsepower motor shall be permitted to control a load not greater than what percentage of the ampere rating?

• A. 50%
• B. 80%
• C. 90%
• D. 100%

Answer: (B)

The main idea here is that general-use snap switches used to control a motor must be derated to leave headroom for the motor’s starting surge. Per 404.14(A), the allowable motor load is limited to 80% of the switch’s ampere rating. This margin helps prevent overheating and contact wear when the motor starts and draws a brief higher current than its running load. For example, if the switch is rated at 10 A, you should limit the motor load to 8 A.

The other options aren’t the rule: 50% would be overly conservative and limit capacity, while 90% or 100% would not provide enough margin for startup surges and could damage the switch over time.