Current Transformers (CT’s) can be used for monitoring current or for transforming primary current into reduced secondary current used for meters, relays, control equipment and other instruments. CT’s that transform current isolate the high voltage primary, permit grounding of the secondary, and step-down the magnitude of the measured current to a standard value that can be safely handled by the instrument. To determine which CT is appropriate for a particular application, it is important to understand the following characteristics that are used to classify current transformers.