A three-phase, 480 V motor is controlled by a magnetic starter with an across-the-line configuration. The motor is rated for 15 kW (approximately 20 HP). The electrician needs to select appropriate overload heaters for the motor. The motor's nameplate indicates a Service Factor (SF) of 1.15 and a Full Load Amperage (FLA) of 27 A. According to the CEC, which of the following is the correct maximum setting for the overload protection if the motor has a service factor of 1.15 or greater?

Question: A three-phase, 480 V motor is controlled by a magnetic starter with an across-the-line configuration. The motor is rated for 15 kW (approximately 20 HP). The electrician needs to select appropriate overload heaters for the motor. The motor's nameplate indicates a Service Factor (SF) of 1.15 and a Full Load Amperage (FLA) of 27 A. According to the CEC, which of the following is the correct maximum setting for the overload protection if the motor has a service factor of 1.15 or greater?

Answer options:

• 27 A
• 30 A
• 31.05 A ✅ 34.1 A

Correct answer: 34.1 A

Explanation: According to CEC Rule 28-306(1) and Table 30, for a motor with a service factor of 1.15 or more, the maximum setting for the overload protection shall not exceed 125% of the motor's full-load current rating. Therefore, 27 A * 1.25 = 33.75 A. The closest available standard heater size without exceeding this value must be chosen, or in this context, the calculated maximum value is 33.75A, so 34.1 A is the closest option if selecting from standard available settings.