A terminal block assembly is provided, comprising a plurality of terminal blocks mounted on a common horizontal support member, including a supply terminal block connected with a voltage source, and a plurality of distribution terminal blocks connected with a plurality of loads, respectively, characterized in that the length and height dimensions of the terminal blocks are the same, but the width of the supply terminal block is greater than that of the distribution terminal blocks, and that the supply conductor contact arrangements of the supply terminal block are designed for connection with a supply conductor having a relatively large cross-sectional area, while the distribution conductor contact arrangements of the distribution terminal blocks are designed for connection with distribution conductors having a relatively small cross-sectional area. A conductive comb member extends transversely across the assembly to interconnect the electrical circuitry contained within the terminal block housings.