Is it an accepted standard to use flexible metallic conduit (in a two wire single phase branch circuit -no separate ground wire-)Is it o.k. to use the flex as ground? Or does it have to be EMT? I am tying in some older (2 wire-hot/common EMT as ground)) Circuits to a new load center and wish to no if this is proper by NEC standards. i want to use flex for the new offsets the circuits have to make.
Is it an accepted standard? In my experience, no. Is it NEC compliant? Yes, provided the ground fault return path is 6ft or less and the fittings and flex you use are listed for grounding. Note that the 6ft. or less is for the entire run of the circuit. For example, you cannot run a piece of conduit with a 6ft flex whip into the panel on one end and a 6ft. whip to a fixture on the other end. That would be a fault return of 12ft. I think most here will agree either keep the run in EMT or pull an equipment grounding conductor.
Re: Flexible metallic conduit for grounding purposes?? #5698 12/08/0112:30 AM12/08/0112:30 AM
Flexible metal conduit not listed for grounding can be used as a ground provided it is less than 6 feet and the fittings are listed for grounding and the circuits are protected at 20 amps or less and it is not installed for flexibility.
Flexible metal conduit listed for grounding can be any length provided the fittings are also listed for grounding.
By the way, has anyone seen how much the UL description of flex fittings listed for grounding and flex fittings not listed for grounding has changed from the 1999 book to the 2000 book? It is quite significant. There appears to be no special determination for steel vs. aluminum using set screw type connectors in the 2000 book like there was in the 1999 book.