What is the minimum size THWN-2 ungrounded feeder conductor required to supply a dwelling unit with a load at 110°F?

To determine the minimum size THWN-2 ungrounded feeder conductor required for a dwelling unit with a specific load at 110°F, understanding the relevant ampacity tables from the National Electrical Code (NEC) is crucial. The ampacity of conductors is influenced by the ambient temperature to which they are exposed. For THWN-2 conductors, the ampacity is reduced as the temperature increases.

At 110°F, the calculated ampacity of a conductor is lower compared to standard conditions (usually 30°C or 86°F). Specifically, the ampacity for THWN-2 conductors needs to be adjusted according to temperature correction factors provided in the NEC.

Based on load requirements and considering the temperature factor for THWN-2 conductors at 110°F, a 1 AWG THWN-2 conductor typically has an ampacity that meets the needs of a standard residential load. Conductors of smaller gauge sizes (like 2 AWG or lower) would not adequately support the necessary load, while larger sizes (like 2/0 AWG) would be more than sufficient but exceed the minimum requirement.

Using ampacity charts, one can confirm that a 1 AWG THWN-2 ungrounded