Load #3 draws 52 amps; the circuit uses a 300-amp breaker and 350 kcmil conductors with 75°C lugs, 4 ft distance to the fused disconnect. What is the smallest size wire permitted between Pull Box 2 and the fused disconnect for Load #3?

Load #3 draws 52 amps; the circuit uses a 300-amp breaker and 350 kcmil conductors with 75°C lugs, 4 ft distance to the fused disconnect. What is the smallest size wire permitted between Pull Box 2 and the fused disconnect for Load #3?

• A. 12 AWG
• B. 10 AWG
• C. 8 AWG
• D. 6 AWG

Answer: (D)

The key idea is sizing the conductor to carry the load current with the protection that protects it. Since the lugs are rated 75°C, you use the 75°C ampacity values. The load for this segment is 52 A, so you need a conductor with an ampacity at least 52 A. From the 75°C column, 8 AWG copper is about 50 A, which is not enough for a 52 A load. The next size up is 6 AWG, which is about 65 A, comfortably meeting the requirement. The short 4 ft run means voltage drop is not a concern here, so the limiting factor is ampacity, not distance. Therefore, the smallest wire that safely conduct Load #3 is 6 AWG.

The key idea is sizing the conductor to carry the load current with the protection that protects it. Since the lugs are rated 75°C, you use the 75°C ampacity values. The load for this segment is 52 A, so you need a conductor with an ampacity at least 52 A.

From the 75°C column, 8 AWG copper is about 50 A, which is not enough for a 52 A load. The next size up is 6 AWG, which is about 65 A, comfortably meeting the requirement. The short 4 ft run means voltage drop is not a concern here, so the limiting factor is ampacity, not distance.

Therefore, the smallest wire that safely conduct Load #3 is 6 AWG.