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?

To determine the minimum size of aluminum THW ungrounded service-entrance conductors required for a 120-ampere load on a 120/240-volt system, it is important to refer to the National Electrical Code (NEC) and the ampacity tables which provide guidance on conductor sizing based on current-carrying capacity.

In this scenario, a load of 120 amperes is specified. For aluminum conductors, one would typically refer to NEC Table 310.16 (or an equivalent resource), which lists the allowable ampacity for different wire sizes based on conductor insulation type and temperature ratings. For service-entrance conductors, it is common to consider a minimum of 75°C insulation for calculating ampacity.

For a 120-ampere load, the NEC indicates that a minimum of 1/0 AWG aluminum conductor is required for this current level. Conductors larger than 1/0 would certainly suffice, but 1/0 AWG meets the minimum requirement for the specified load. Therefore, the inclusion of 1/0 AWG in the correct answer reflects compliance with NEC requirements for safe and effective electrical installations.

The other sizes offered, while larger than 1/0, exceed