What is the minimum conductor size for a circuit with six conductors connected to a 75° C rated circuit breaker, each carrying a 70 amp load?

For a circuit with conductors carrying a 70 amp load each, the minimum conductor size must be determined based on the ampacity provided in the NEC (National Electrical Code) tables, specifically for conductors rated at 75° C.

According to NEC guidelines, a conductor's ampacity can vary based on the number of conductors in a raceway or cable. Among the options provided, 4 AWG is the suitable size for this particular scenario. The 4 AWG conductor typically has an ampacity of around 85 amps when considered under the 75° C rating. This size provides a safe margin above the 70 amp load each conductor is carrying, allowing for some additional capacity to prevent overheating.

Selecting a proper conductor size ensures that the circuit operates safely and efficiently, adhering to the regulatory standards that prevent overheating, possible insulation failure, and potential fire hazards. Additionally, while the other choices are insufficient to handle the load based on NEC guidelines, the 4 AWG conductor chosen has the necessary capacity to safely support the circuit's requirements.