Square D PowerPactH, J and L-frame circuit breakers are designed to protect electrical systems from damage caused by overloads and short circuits Molded case circuit breakers are available with either thermal-magnetic or Micrologic electronic trip units. L-frame breakers are performed only with Micrologic electronic units The pocket tester connects to the Micrologic trip unit test connector. It powers up the Micrologic trip unit and the Ready LED. It supplies the screen, allows settings to be made using the keypad, and provides thermal imaging inhibit functions. The pocket tester runs off of two Alkaline AA batteries.