What conductor size is recommended for aluminum conductors in a residential service-entrance at 120 amperes?

The recommended conductor size for aluminum conductors in a residential service entrance rated at 120 amperes is 1/0 AWG. This sizing ensures safe and efficient performance while minimizing the risk of overheating.

Aluminum conductors require larger sizes compared to copper to carry the same amount of current because they have a higher resistance. According to the National Electrical Code (NEC), for an application like a residential service entrance with a 120-ampere load, 1/0 AWG aluminum is appropriate. This size provides the necessary current-carrying capacity and is compliant with safety standards.

Using a larger size conductor, such as 4/0 AWG or 3/0 AWG, might be overkill unless there are special conditions or future load increases expected, which could lead to unnecessary costs and complexity in installation. On the other hand, smaller sizes like 2 AWG would not meet the necessary current ratings and could pose a safety hazard due to the risk of overheating under continuous load. Thus, 1/0 AWG represents a balance of safety, compliance, and cost-effectiveness for this application.