A subsystem (200) for a circuit breaker unit (100) and a circuit breaker (10) includes a base assembly with a base plate (108) carried by a bottom surface (104), the base plate (108) being dimensioned to receive the circuit breaker (10), and the bottom surface (104) being configured to form a part of a shelf section (102) of the circuit breaker unit (100). An adapter assembly includes an adapter plate (202) and a plurality of conductors (114) detachably connected at a first side to the adapter plate (202), the adapter plate (202) being detachably connected to the base plate (108). When assembling the circuit breaker unit (100), the adapter plate (202) is removed from the base plate (108) and replaced with the circuit breaker (10) including detaching the plurality of conductors (114) from the adapter plate (202) and attaching the plurality of conductors (114) to the circuit breaker (10).
