The major problems with FMC are those associated with supporting it (keeping it from flopping around or snagging on something) and causing the wiring inside to flex and break. That's remedied by providing the proper number of supports per unit length. If that's done, the overall length isn't an issue.
Proper support is my concern. I see contractor dumping FMC into a congested hung ceiling, sitting on ceiling grid without any proper support. The cable is pulled when nobody around. That should be limited to shorter length and used for connection to equipment for flexibilty only.
As an electrician who has to work on garbage like that, I definitely understand your complaint. But flexible wiring methods are already supposed to be secured and supported, so the guys who are installing it that way are already violating electrical code. Adding additional codes limiting the length would just be one more thing for them to ignore.
The code is written ostensibly for safety, and while I might not like long lengths of FMC, I can't reasonably say they present any hazard when installed correctly.
The upper length limit for any sort of raceway (flex, rigid, whatever) wil be the tension required to pull conductors through it. In any case, as long as the wire manufacturer's limits are adhered to (and the raceway is secured to withstand the forces involved) all is well.
Since pulling tension depends (among other things) on the number and radius of bends, I would suspect that the maximum length of FMC through which a given wire bundle could be pulled is somewhat less than that of rigid conduit. But that's up to the engineer's analysis or experience of the electrician. The code just says don't break it.
The CBC (california) limits FMC to 6' lengths. however, this can be
modified/changed by the EE, by insuring that there is a grounding conductor within the flex.
The reasoning behind the short lengths is grounding (who would have thought).
The CEC, NEC, NFPA all have listed locations where you can not have Flex, not be confused with liquatite, such as, but not limited to, underwater, battery rooms etc.
steve
Inspector Steve
DSA, OSHPD, Inspector
So. California.
