Connect cables directly to 3/8" threaded rod in trapeze installations for seismic bracing. Predrilled tabs allow attachment directly to concrete deck. Spacing must be at least every 30'. High-seismicity projects place much greater demands on cable tray systems than ordinary installations. During an earthquake, cable trays are exposed not only to gravity loads and normal service loads, but also to lateral movement, vertical acceleration, vibration, and building drift. When an earthquake happens, the ground really shakes. These guidelines summarise the design parameters, criteria.