What is the minimum size ungrounded service entrance conductor for a 120-240 V single phase 200 amp service in a commercial building?

For a 120-240 V single-phase 200 amp service, determining the minimum size ungrounded service entrance conductor is critical for safe operation and compliance with the National Electrical Code (NEC) standards. According to NEC guidelines, the size of the conductor must take into account both the ampacity of the conductor material and the application.

In this instance, when using copper conductors, the typical minimum size required for a 200 amp service is 3/0 THWN (Thermoplastic Heat & Water Resistant Nylon). This gauge provides sufficient capacity to handle the load while also taking into account factors such as temperature rating and insulation type.

Using 3/0 THWN copper ensures that the conductor can safely conduct the required current without overheating and maintains a reasonable voltage drop over the length of the run. This is particularly important in commercial buildings where load demands can vary significantly.

The other options, while they may offer different ampacities, do not meet the requirements set by the NEC for a 200 amp service utilizing this specific voltage and phase configuration. Therefore, the choice of 3/0 THWN copper is not only compliant but also prudent for ensuring operational safety and efficiency in commercial applications.