A technician is installing a new 45 A, 208 V, three-phase motor on a permanent basis in a dry industrial environment. The motor leads are connected to a junction box containing the circuit conductors, which are run in rigid metal conduit (RMC). The circuit conductors are 75 °C insulated copper. Which of the following conductor sizes is the minimum permissible for this motor branch circuit, considering continuous operation and standard overcurrent protection?

Question: A technician is installing a new 45 A, 208 V, three-phase motor on a permanent basis in a dry industrial environment. The motor leads are connected to a junction box containing the circuit conductors, which are run in rigid metal conduit (RMC). The circuit conductors are 75 °C insulated copper. Which of the following conductor sizes is the minimum permissible for this motor branch circuit, considering continuous operation and standard overcurrent protection?

Answer options:

• No. 10 AWG copper
• No. 8 AWG copper ✅ No. 6 AWG copper
• No. 4 AWG copper

Correct answer: No. 6 AWG copper

Explanation: CEC Rule 28-106(1) states that conductors for motor branch circuits must have an ampacity not less than 125% of the motor's full-load current (FLC). For a 45 A motor, 1.25 x 45 A = 56.25 A. According to CEC Table 2 (75 °C column), a No. 6 AWG copper conductor has an ampacity of 65 A, which meets this requirement. No. 8 AWG has an ampacity of 50 A, which is insufficient.