What is the minimum size THWN aluminum service conductor permitted by Code to supply a 400-ampere, 120/240-volt service to a single family dwelling?

To determine the minimum size of a THWN aluminum service conductor suitable for a 400-ampere, 120/240-volt service to a single-family dwelling, it is essential to refer to the National Electrical Code (NEC) ampacity tables and consider any applicable derating factors.

For a 400-amp service, the NEC specifies that THWN aluminum conductors have a certain ampacity based on their size. According to the NEC, a 600 kcmil THWN aluminum conductor has an ampacity that meets or exceeds the requirements for a continuous load at 400 amps.

This size ensures that the conductor can handle the load without overheating or causing safety hazards, allowing for a margin of safety and compliance with the Code. Additionally, it's important to consider that different conditions, such as the installation environment and temperature, can affect the effective ampacity.

When assessing a service load like this, choosing a conductor that is not just sufficient for the load, but also accounts for these potential variables is crucial for safe and reliable electrical service. Therefore, a 600 kcmil conductor is the minimum size deemed appropriate by the Code to supply safely and efficiently the required 400 amps for the specified dwelling service.