An industrial facility requires the installation of a new 480 V, three-phase, 15 kW motor. The motor is located in an area with an average ambient temperature of 50°C. The proposed conductors are 14 AWG copper, R90 cable. After applying the motor conductor sizing rules and temperature correction factors, which of the following statements is true regarding the conductor sizing based on CEC?

Question: An industrial facility requires the installation of a new 480 V, three-phase, 15 kW motor. The motor is located in an area with an average ambient temperature of 50°C. The proposed conductors are 14 AWG copper, R90 cable. After applying the motor conductor sizing rules and temperature correction factors, which of the following statements is true regarding the conductor sizing based on CEC?

Answer options: ✅ 14 AWG copper conductors are generally too small for a 15 kW motor, even before temperature correction.

• 14 AWG copper conductors are adequate after applying the temperature correction factor.
• A smaller gauge conductor (e.g., 16 AWG) could be used if the motor operates intermittently.
• Temperature correction factors are only necessary for conductors exposed to direct sunlight.

Correct answer: 14 AWG copper conductors are generally too small for a 15 kW motor, even before temperature correction.

Explanation: First, calculate the full-load current (FLA) for a 15 kW, 480 V, 3-phase motor. Using FLA tables (or formula P = √3 * V * I * PF * Eff), a 15 kW (approximately 20 HP) motor at 480 V typically has an FLA around 21-24 A (referencing CEC Table 44 for 460V motors, 20 HP is 27A). Conductor sizing for motors requires 125% of FLA (Rule 28-106(1)). So, 27 A * 1.25 = 33.75 A. 14 AWG R90 has an ampacity of 25 A (Table 2). After correction for 50°C (Table 5C, factor 0.75 for 90°C), its ampacity becomes 25 A * 0.75 = 18.75 A. This is far below the required 33.75 A, making 14 AWG significantly too small, even before considering high ambient temperature. Therefore, statement A is true.