A motor load not exceeding what percent of the amp rating of the snap switch at its rated voltage is permitted to be controlled to this load?

A motor load not exceeding what percent of the amp rating of the snap switch at its rated voltage is permitted to be controlled to this load?

• A. 50%
• B. 60%
• C. 100%
• D. 80%

Answer: (D)

When a switch is used to control a motor, you can’t treat the motor current as just a steady, resistive load. Motors have a high inrush and inductive surge when they start, which can push currents above the running current. To protect the switch from overheating and wear, the motor load must be limited to a portion of the switch’s amp rating at the rated voltage. The established derating is 80%. That means the motor’s running current should not exceed 80% of the switch’s rated amperage. For example, if the motor runs at 6 A, you’d want a switch rated for at least about 7.5 A (6 A is 80% of 7.5 A). Using a higher percentage, like 100%, would leave no margin for startup surges; a lower percentage (like 50–60%) would be overly conservative and could prevent the motor from starting properly.

When a switch is used to control a motor, you can’t treat the motor current as just a steady, resistive load. Motors have a high inrush and inductive surge when they start, which can push currents above the running current. To protect the switch from overheating and wear, the motor load must be limited to a portion of the switch’s amp rating at the rated voltage. The established derating is 80%. That means the motor’s running current should not exceed 80% of the switch’s rated amperage. For example, if the motor runs at 6 A, you’d want a switch rated for at least about 7.5 A (6 A is 80% of 7.5 A). Using a higher percentage, like 100%, would leave no margin for startup surges; a lower percentage (like 50–60%) would be overly conservative and could prevent the motor from starting properly.