Spacing Standards: Electrical (power) and instrumentation (signal/control) cable trays should maintain a minimum vertical and horizontal distance. Dividers or Partitions: Where. a) In general, vertical spacing for cable trays should be 12 in (30. 5 cm), measured from the bottom of the upper tray to the top of the lower tray. A minimum clearance of 9 in (22. Unlike power cables, instrumentation cables generally transmit. maintain spacing or to keep cables in place when the tray is ect the minimum bend ra-dius for cables as they exit the bottom of the cable tray.