In general, vertical spacing for cable trays should be 30 cm (12 in), measured from the bottom of the upper tray to the top of the lower tray., to facilitate installation of. Cable tray (or cable ladder) systems are a popular alternative to electrical conduit systems, as they have an outstanding record for dependable service, design flexibility and cost savings in commercial and industrial applications. A properly designed and installed cable tray system will provide. When installing two cable trays in parallel at the same height, the distance between them should be no less than 0. The Ladder Tray features light, rugged, tubular steel construction. The NEC has a requirement for ladder-type cable trays.