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.