68 engaging the aligned stringers 12 13 and 20 cover panels 16 17 and 17 a are then urged inwardly against the associated panel frame 9 so that the barb 73 on clips 68 engage aligned windows 52 in horizontal stringers 12 13 and 20 to securely yet removably mount the same in place cover panels 16 17 and 17 a are thereby positioned against or adjacent the outer faces 40 of horizontal stringers 12 13 and 20 thereby enclosing or completing the horizontal raceway cavities 14 and 15 each of which has a vertically elongated shape when viewed in end elevation the two horizontal raceway cavities 14 disposed between horizontal stringers 12 and 20 are located adjacent work surface height and define beltway raceway cavities the two horizontal raceway cavities 15 disposed between horizontal stringers 12 and 13 are located adjacent to the panel base and define lower raceway cavities the illustrated stacker panel 6 fig3 and 16 has a construction substantially similar to previously described base panel 5 except that it does not have a foot 11 or an intermediate pair of stringers 13 stacker panel 6 also comes in a variety of different widths as well as various heights and mounts directly on top of an associated.