Cable Types: Only use conductors rated for open-air environments, such as Tray Rated (Type TC) or Metal-Clad (Type MC) cables. These systems, made from metal or plastic, are open structures designed to support electrical conductors, ensuring proper organization and safety. Consider future expansion needs to accommodate additional cables. Layout. This guide will walk you through the simple, clear principles for getting cable trays wiring right. Cable trays are like special roads for wires. Ampacity Derating. Our name originates from the OBO anchor: Until 1952, there was no way around it – anyone wanting to put an anchor into the wall had to drill a hole. However, OBO engineers were not satisfied with this and developed a metal anchor, which could simply be knocked into the wall.