Which of the following category ratings would a meter need to have to take voltage readings at the service switch gear of an industrial facility?

In industrial settings, particularly when dealing with service switch gear, the appropriate category rating for a meter is CAT III. This rating signifies that the equipment is designed to be used in environments where it can be subjected to higher transient voltages, which are typical in service switch gear applications.

CAT III meters are suitable for use on building installations, including distribution panels, feeders, and branch circuits, all of which are common in an industrial facility's service switch gear. This rating indicates that the equipment can handle voltages up to 1000V and is designed to provide a higher level of safety and reliability when measuring electrical parameters in these environments.

Using a meter with a lower category rating, such as CAT I or CAT II, would not provide the necessary protection or safety margin, making it unsafe and potentially damaging under the high voltage conditions present at an industrial service switch gear. CAT IV meters are intended for higher-risk environments, such as outdoor overhead lines and transformers, but they are typically not needed specifically for switch gear applications, where CAT III is appropriate.