Spacing Standards: Electrical (power) and instrumentation (signal/control) cable trays should maintain a minimum vertical and horizontal distance. It also helps reduce the risk of. The following are a few points to consider when dealing with cable tray and the National Electrical Code. Separation of Electrical and Instrumentation Cables Electrical on Top, Instrumentation Below: Typically, electrical trays are positioned above instrumentation trays. Use this tool to estimate sloped section length, horizontal run requirement, cut marks, and installation feasibility.