What category rating is necessary for three-phase distribution, including single-phase commercial lighting?

A category III (CAT III) rating is necessary for three-phase distribution systems and single-phase commercial lighting because this rating is designed for equipment that is typically subjected to higher voltages and more severe conditions in the electrical distribution environment. CAT III includes systems installed in commercial and industrial buildings, meaning it deals with distribution panels, feeders, and service entrances where three-phase power is common.

This category rating reflects the potential exposure to higher transient voltages and the need for equipment capable of withstanding those conditions. Equipment with a CAT III rating is tested to endure the electrical surges that can occur in commercial lighting and distribution systems, ensuring safety and reliability for personnel working with or near such electrical systems.

In contrast, other category ratings such as CAT I and CAT II cater to less hazardous environments, such as the output of a single outlet or equipment that is directly fed from a low-voltage supply, where the risk of transient surges and higher voltages is significantly lower. CAT IV, while higher than CAT III, is generally reserved for equipment directly connected to the utility service, which isn't applicable for the specified three-phase distribution applications in this question.