The URC B-291 Secondary Injection Set is a single-phase test set specifically designed for testing the operation of the AC-PRO microcontroller based trip units manufactured by Unity Relay Co. The test set will test the standard AC-PRO trip unit configured for 1-amp secondary current transformers (CTs) or special AC-PRO trip units configured for other secondary CT ratings. The unit can test pick-up and time delays of the various protection functions of driving current into the AC-PRO in the secondary side of the CT circuit. The URC B-291 will test 60, 50, 40, or 25 Hertz AC-PRO trip units. It will test the AC-PRO trip system with the exception of the CTs and associated wiring harness.