The Code uses the phrase "insulating bushing or its equivalent protection shall be provided between the conductors and the armor". For type AC (as previously mentioned)See section 320.40
3/8" FMC is addressed in Article 348 of the NEC.Conductor fill is covered in Table 348.22 make note as to whether you are using connectors that are internal or external.
Grounding requirements are covered in 348.60 Where used to connect equipment where flexibility is required, an equipment grounding conductor shall be installed. If you install one it counts as conductor fill.
Also Article 250.118 recognizes FMC as an equipment grounding means if the conduit and the fittings are listed as such. Or you could be useing FMC that is listed, but not listed as a grounding means(and it’s probably not) under the following conditions. The total length (return path) is not greater than 6 feet, the fittings are listed for the purpose (few check), and the conductors are protected at 20 A or less. Of course it can not be installed to provide flexibility, and function as a EGC.
Note that section 348.42 does not mention insulating bushings. But then again the NEC is only a minimum standard!
[This message has been edited by cpal (edited 08-06-2004).]
[This message has been edited by cpal (edited 08-06-2004).]