Primary Injection Test Sets Designed using the latest technology, these units combine a variable high current output with the appropriate controls and instrumentation. The test set is ideal for testing Current Transformers (CTs), High Current Panel, thermal, magnetic, and solid-state motor overload relays as well as moulded-case circuit breakers and ground fault trip devices. They can also be used in many other applications requiring a high current source. Instrument working on the principle of varying the power in the primary circuit of the matching power transformer and, respectively, varying the output current, flowing through the automatic circuit breaker under the test.