What is the minimum size of aluminum THW ungrounded service-entrance conductors required for a dwelling unit with a load of 120 amperes on a 120/240-volt system?

For a dwelling unit with a load of 120 amperes on a 120/240-volt system, the National Electrical Code (NEC) provides guidelines for the sizing of conductors to ensure safety and efficiency in electrical installations. In this scenario, using aluminum THW (Thermoplastic Heat and Water Resistant) conductors, the minimum size required is determined by the ampacity tables.

According to NEC tables, for aluminum conductors, the minimum ampacity for a 120 amp load indicates that 1/0 AWG is sufficient. The reasoning is based on the conductor's ability to safely carry the current without overheating and ensure proper performance under load conditions. Each conductor size has a specific ampacity rating that corresponds to its thermal and physical characteristics and how it can operate within a circuit.

More specifically, when dealing with a 120 amp load, 1/0 AWG aluminum conductors can carry the necessary current while maintaining safe operating temperatures and comply with all relevant safety standards. Larger sizes like 2 AWG or 3/0 AWG would exceed the requirements, and 4/0 AWG is significantly over-sized for this load.

Understanding the relevant NEC tables and determining ampacity is crucial in selecting the correct conductor size