of the center rails 14 the bus bars 17 18 which support the circuit breaker stab connectors 19a 19f are secured between the center rails and the side rails by slightly displacing the center and side rails from the vertical as illustrated in phantom to allow the bus bars to fit within the elongated slots then allowing the side rails and center rails to return to their rest positions to trap the edges of the bus bars within the slots the provision of a locking tab 23 at one end of the bus bars and a corresponding vertical slot 24 in the side rails allows the tabs to swing within the slots when the edges of the bus bars are positioned within the elongated slots 15 to assist in lockingly retaining the bus bars on the plastic base prior to securing the bus bars to the plastic base a threaded lug 21 is inserted within the opening 22 formed within each bus bar to provide electrical attachment to the bus bars as shown in fig2 the flattened ends 25 of the lugs 21 are trapped within the opening 20 formed within the plastic base 11 and the bottom of the bus bars 17 and 18 the locking tabs 23 are shown projecting through the slots 24 in the side rails 13.