An appliance includes a cabinet and a shelf assembly. The shelf assembly includes a lead screw mounted to the cabinet such that the lead screw is rotatable. A shelf support is mounted to the cabinet such the shelf support is translatable relative to the lead screw. The shelf support has a housing. A nut is disposed within the housing of the shelf support and is threaded on the lead screw. The nut has a plurality of teeth at an outer surface of the nut. A locking plunger has at least one tooth. An actuator is coupled to the locking plunger. The actuator is operable to selectively mesh the at least one tooth of the locking plunger with the plurality of teeth of the nut.