Cables,AC.MC.FMC, bushings
Some questions concerning types and differences of armored cable, type AC; metal clad cable, type MC; flexible metal conduit, type FMC, and insulating bushings. First, I finally used all of my Borders gifts cards and bought an NEC code book. :D That being said I still have several questions. I read through the sections for AC cable (320) and MC (330).
1. While there are obvious differences, permitted uses, etc. the most significant appears to be that under 330.116 for MC, it allows for different sheaths. For example, the smooth metallic sheath, is that actually a flexible metal or a metal impregnated vinyl/metal?
2. Is the AC cable what is commonly referred to as BX? People seem to use terms interchangeably.
Also need info on FMC and the use of the plastic insulating bushings. I was told that these should be used on FMC. However, I have learned that what is sometimes practiced in the field is not necessarily needed per code. Nowhere in 348 do I see this requirement listed. Only in 320.40 for AC do I see a reference to insulating bushings. While the use of the bushings with FMC makes sense, it would appear to conflict with the explanation under 348.26 which states in part”…this flexible wiring method ensures that conductors can be easily installed or withdrawn at any time.” With bushings installed it would seem to me that removing wires wouldn't be a problem, but if using a fish line it could jam against the bushing. Any thoughts, suggestions, pros-cons, etc. on their use with FMC?