For a 120/240-volt, 1-ph, 3-wire service to a 100-Amp service, what is the smallest neutral conductor that can be installed?

To determine the smallest neutral conductor size for a 120/240-volt, 1-phase, 3-wire service to a 100-Amp service, it's essential to reference the National Electrical Code (NEC) guidelines, particularly those relating to the sizing of conductors.

When calculating the size of the neutral conductor, one must consider the current-carrying capacity relative to the load. Typically, for feeders and services, the neutral conductor may be sized based on the expected maximum load it needs to handle. The NEC provides specific guidelines that state for non-multifamily dwellings, the minimum allowable size for a neutral wire can be less than that required for ungrounded conductors.

For a 100-Amp service, the neutral size can typically be evaluated based on a percentage of the ungrounded conductors or a dedicated sizing table for service disconnects. In this particular situation, the neutral conductor is sized assuming no significant unbalanced load. According to NEC tables, an 8 AWG copper conductor is adequate for the application, meeting the minimum requirement for current carrying capacity for the neutral conductor in a 100-Amp service.

This means that 8 AWG is indeed the most suitable size for the neutral in this scenario