This wiring method is the surface metal raceway. It's a metallic raceway that's supposed to be mounted to the surface of a structure [386.2]. Generally, this raceway has very high aesthetic value. It's meant to be installed as a system, using the couplings, connectors, boxes, and fittings for that particular system.
There are four permitted uses. They are: In dry locations; in Class I, Division 2 hazardous locations as permitted in 501.10(B)(3); Under raised floors, as permitted in 645.29(1), and extending through walls and floors (this last one has conditions for permissibility) [386.10].
There are actually five uses not permitted. Where subject to severe damage; where subject to corrosive vapors; where the voltage between conductors is 300V or more (unless specific special circumstances exist); in hoistways; where concealed (except as permitted in 386.10) [386.12].
- Secure the raceway per the manufacturer's installation instructions [386.30]. Note that deviating from these instructions may well produce an installation that violates the listing of the components. They are meant to be assembled and supported in specific ways, and they are tested with those assembly and support means to get their testing lab listing.
- You can use only listed components [386.6]. Maybe something you'd normally use for EMT would handily solve an installation problem, but using it would render the installation out of compliance with the Code. You can't "field-design" these systems.