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under 348.26 which states in part”…this flexible wiring method ensures that conductors can be easily installed or withdrawn at any time.”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?

Yes, MC cable does come plain metal and with various vinyl jackets. There is one for example rated to be embedded directly in wet concrete. This is popular for poured concrete floor of parking garages, as the base is usually a precast unit needing a poured covering. Cables go from light to light, no conduit.

The most popular is the metallic used in steel studded and steel frame construction.

AC cable is the technical term for the popular BX, which I understand is a GE brand name from many years ago.

Any metallic raceway with wires #4 or larger all require insulated bushings, per NEC 300.4 (F)

Sec 320.40 refers to insulated bushings in respect to the "Redheads" or anti short bushings, those little split bushings you push into the end of the cable around the wires to keep the cut metal sheathing from cutting into the wires.

As far as FMC, when you must use insulated bushings fall under 300.4 (F). Bushings are made for smaller size conduits as a good installation will exceed Code, and many times are required by the design engineer.

Installing a fish tape does not concern the code, a properly prepared hook on a fish tape will not get stuck anywhere.

FMC is used when absolutely necessary, not used often for runs too long.

Hope this helps

Thanks for the response, it did help. Still navigating and trying to interprete the code :eek: I did initially read the 300 section but still trying to tie all the sections and references together. As for the FMC, only used in short sections and for whips, but I always used the bushings even though I use a professtional cutting tool. I tend to carry my installs to the extreme so to limit the chance for furture problems. I was just wondering if they were really necessary as it appeared not required in the code based on the 14 ga wire-I feel better using them.

Did you get the NEC handbook or just the actual code without photos, diagrams, and commentary?

Did you notice in the "Read First" sticky I provide a link to the NEC, available for review?

I got the NEC book with diagrams and commentary which provides a lot of detail. However, something's still appear open to interpretation. I found another help site (mikeholt.com) where you have to in some manner work in the electrical industry, and there are still tons of code questions. Sorry, I missed the sticky, looks very helpful. Thanks for the info tk...

Something open to interpretation? With the Code? No way!

Sorry for the sarcasm, that is the strong point of the code , open to interpretation,It is difficult for thew code to cover every little thing in the real world, so needless to say, there are a lot of questions.

Tk-no problem-"interpretation" was a poor word choice. I was trying to say what you stated-that there are still a lot of questions in real world applications. Thanks, shader