The unique auto-sensing feature makes these testers easy to operate. Sensing leads, which operate on either normally-open or normally-closed devices, are connected to the test object. The output current level can be easily pre-set. When the output is initiated, the pre-set output current locks on and the timer starts. When the test set senses a change in state of the test object (NO to NC or NC to NO), the current shuts off and the timer stops. For instantaneous trip tests, the memory feature of the currentmeter holds the peak current value until reset by the operator.