Abstract: A preset block assembly adapted for use with an underfloor electrical distribution system having one or more electrical conductors enclosed in elongated, laterally spaced cells. The block assembly includes a housing having a terminal portion that rests on the top wall of one of the cells and encloses an opening therein. In one embodiment, the housing has depending portions at each end thereof which seat in valleys defined by cells on each side of the central cell of a set of three. In another embodiment, the housing has only one depending portion which seats in the valley between a pair of the cells. In both embodiments, an outwardly extending sleeve on the side wall of the depending portion or portions extends into an opening in the side wall of the cell or cells adjacent to the cell underlying the terminal portion.