This isn't a wiring method in the sense we typically think of one. It's the low-voltage suspended ceiling power distribution system [393.1], and such a system replaces wiring methods. It does away with a lot of ad hoc design and greatly simplifies installation. The result is a neater, more reliable installation at a lower cost. At the heart of it is a "box" that serves as a sort of hub for distributing power to utilization equipment supplied by a Class 2 power supply. See my article on these systems in the May, 2014 edition of EC&M Magazine, www.ecmweb.com
First of all, it has to be permanently connected [393.10]. It can supply listed utilization equipment operating at up to 30VAC or 60VDC in dry locations indoors. It can be used in residential, commercial, and industrial applications. It can be used in other spaces used for environmental air (see 300.22(C)).
You can't use it in damp or wet locations, where subject to corrosive fumes or vapors, where subject to physical damage, in concealed locations, in hazardous locations, as part of a fire-rated assembly (unless specifically listed as part of the assembly), or for lighting in general (or critical patient) care areas.
- Use the mounting hardware that comes with it or the mounting fasteners specified in the instructions [393.30]. You can secure it to the mounting surface of the building by hanging wires, screws, or bolts in accordance with the installation instructions.
- Use listed insulating devices when making connections to busbar grid rails, cable,s and conductors. The connections must remain accessible (see Article 100 definition of accessible). You can use any of the four connector types specified in 393.40(A).