A cable retaining ring includes a base having at least one mounting opening or at least one mounting projection for connecting the cable retaining ring to a cable support tray, an elongate interior defining a cable retention region, a gap through the ring for allowing a cable to be placed into or removed from the interior, and a slide mounted on the ring and shiftable between a first position substantially blocking the gap to prevent the cable from being placed into or removed from the interior and a second position unblocking the gap.