National Electrical Code Articles and Information

1. Armored Cable (Type AC).
    

2. There are five: for feeders and branch circuits in concealed or exposed installations, in cable trays, in dry locations, embedded in plaster or brick or other masonry but not in wet or damp locations, in the air voids of masonry where dry [320.10].
    

3. There are five: where subject to physical damage, in damp or wet locations, in voids subject to moisture, where exposed to corrosive conditions, embedded in plaster or brick or other masonry if in wet or damp locations [320.12].
    

4. It can't be less than five times the diameter of the cable [320.24]. However, this doesn't mean the "final" bending radius. It means that you do not exceed this at any time during the installation process. Once this radius is exceeded, the AC Cable is irreparably damaged.
    

5. Support is a huge issue. Support requirements are not reduced by dint of using Type AC Cable. Subsection 320.30, which provides the support requirements for Type AC Cable, is the largest subsection in Article 320. Type AC cable isn't indestructible. It may help to think of is as a flexible version of wire that's been run in EMT or rigid. The walls of the raceway (the metal jacket is really an integrated raceway, making the wire and jacket a wiring system) are thinner, in this case. So the need for support and damage protection are, if anything, greater than for tubing or conduit.