Abstract: The apparatus includes a housing having electrical bus conductors therein and a plug-in module for providing an electrical connection between selected ones of the bus conductors and a circuit board having electrical contacts thereon. The module has an opening therein to receive the circuit board and the module is detachably secured to the housing. The module has leaf-type conductors therein forming the connection between the selected bus conductors and the electrical contacts on the circuit board inserted therein. A camming lever is included in the module to expand the leaf-type conductors to permit removal of the circuit board and side insertion of the circuit board, which camming lever also locks the circuit board to the module to prevent its removal except when the leaf-type conductors are expanded.