When metering the load side of a transformer supplying 120/208v 3-phase, what is the minimum category meter to be used?

In electrical testing, particularly when dealing with transformers and three-phase systems like a 120/208V setup, the safety of the technician is paramount. The correct answer is Category III because it is designed for use in commercial and light industrial environments and covers circuits rated up to 1000V.

When metering the load side of a transformer, the conditions present can expose the technician to potential electrical hazards, including transient overvoltages and fault currents. Category III meters are equipped to handle these high energy levels and provide adequate protection against electrical shocks and equipment damage. They are ideal for measuring the output of distribution circuits which is relevant for assessing transformers as these environments may include larger conductors and higher fault currents.

Category I meters are intended for use in protected areas, while Category II covers appliances and portable equipment with lower energy levels. Category IV is meant for measuring at the source of low-voltage installations, including utility connections, and is not typically the environment encountered when working directly with load circuits of transformers.

Using a Category III meter ensures compliance with safety standards and best practices for measuring electrical currents in these settings. Therefore, it is the optimum choice for metering the load side of a transformer in a three-phase system.