Abstract: A tester for testing a circuit breaker includes a plurality of load elements each having a nominal fixed impedance and an electronic switch associated with each load element. The electronic switch, when turned on, electrically connects a corresponding load element in series with a circuit breaker load terminal and in parallel with none or with a number of other load elements. A controller turns on a number of the electronic switches selected to draw through a corresponding number of the load elements a test current selected as a function of a designated rated current for the circuit breaker and sufficient to trip open the same. A pulse width modulation circuit cooperates with the controller and with the electronic switches. The pulse width modulation circuit provides a constant magnitude of the test current to accommodate variations of the nominal fixed impedance or variations of the voltage of the load terminal.