How are MC, AC (BX) and NM (Romex) cables required to be secured?

     MC (Metal Clad Cables) contains equipment grounding conductors.  The smallest size available according to the NEC that shall be used is # 18 awg copper.  Note that some fire rated conductor material is of nickel or nickel-coated copper.  There is also cable used for Optical Fiber called MC-OF.  The size of the equipment grounding conductor is sized based on Table 250.122 of the National Electrical Code however when part of a cable assembly such as MC, AC, BX, or Romex, NM cable the size required is already determined for you.  The allowable ampacity of the conductors in MC or Metal Clad Cable shall be determined by the appropriate allowable ampacity table.  When securing, MC cable must be supported in new construction within 12 inches of the box and not exceeding 6 feet intervals.  AC or BX on the other hand shall be supported also within 12 inches of the box but not exceeding 4 1/2 ft intervals.  For finished spaces not more than 6 Ft or where its impractical such as in a concealed wall then no supports down or in that wall are required.

     A common mistake is to believe that NMC means nonmetallic conduit which is not true.  NMC is a type of nonmetallic-sheathed cable.  There are three types of nonmetallic sheathed cables.  NM which contains a nonmetallic jacket, NMC a nonmetallic jacket with Corrosion resistance, and NMS which is used for signaling purposes with a nionmetallic jacket.  Romex or NM cable can be used for One and two family dwellings as well as multifamily dwellings.  In NYC Romex can be used when not exceeding three floors above grade.  Romex doesn't have fire protection and is also not allowed in nonresidential buildings in NYC. 

     When passing through a floor NM cables NMC or NMS shall be protected using Rigid, IMC, EMT or Schedule 80 PVC at least 6 inches above the floor.  In unfinished basements and crawl spaces cables containing at least 2 #6 awg or 3 #8 awg or larger shall be secured to the lower edges or the joist.  All other cables shall pass through bored holes.  When securing horizontal or vertical runs securing is the same as AC cable, 12 inches from the box and 4 1/2 feet there after.  But what of underground installations?  Underground wiring or UF cable falls under article 340 Underground Feeder and Brach Circuit Cables which cannot be used in NYC for Direct Burial.