Used controller in Ohio, USA

Verify the nameplate ratio and accuracy class, inspect for physical damage or oil leaks, request recent ratio and insulation test reports, and confirm the CT type (wound/window/bar) and its knee-point if used for protection.

Drain and seal oil-filled CTs if required, protect bushings and cores, short and ground the secondary terminals, secure the unit to prevent shock, and use a carrier experienced with electrical equipment plus insurance.

Perform visual inspections, insulation resistance tests, ratio and polarity checks, check for oil contamination on liquid-filled units, and schedule periodic accuracy and dielectric tests per manufacturer guidelines.