If a single-phase feeder load is calculated at 100 amperes, what is the minimum size THWN copper conductor that must be installed?

To determine the minimum size THWN copper conductor required for a single-phase feeder load of 100 amperes, it is essential to refer to the National Electrical Code (NEC) and the ampacity tables that indicate the current-carrying capacity of different conductor sizes.

In general, according to NEC Table 310.16 (and considering typical conditions such as three conductors in a raceway at an ambient temperature of 30°C), a No. 1 AWG copper conductor has an ampacity rating of 130 amperes. This rating indicates that it can safely carry 100 amperes without overheating, making it the appropriate size for this load.

Choosing a conductor that is rated above the calculated load (in this case, 100 amperes) not only ensures safety but also provides a margin for any potential increases in load due to future expansion or unforeseen circumstances. The other conductor sizes, such as No. 2 AWG, No. 3 AWG, and No. 4 AWG, have lower ampacity ratings (for instance, No. 2 AWG is rated for 115 amperes, No. 3 AWG for 100 amperes, and No. 4 AWG for 85 amper