This accessory is intended for wire cable trays comprising longitudinal warp wires and transverse weft wires linking the warp wires, the wire cable tray having a bottom adapted to receive electric cables or the like and two side flanges. The accessory comprises an upper face (4) raised by at least two feet (2). The upper face (4) comprises not only two first housings (10) disposed parallel to each other and each adapted to receive a weft wire but also at least one housing (12) substantially perpendicular to the first two housings (10). At least one locking device (16) is provided on each side of a median line between the first two housings (10).