FLEXIBLE-METAL-CONDUIT WIRINGFLEXIBLE-METAL-CONDUIT WIRING166. Flexible metal conduit can be used for many kinds of wiring, being in some cases preferable to rigid conduit (see Fig. 9.73). Its installation is much easier and quicker than the installation of rigid conduit, the latter coming in short pipe lengths, whereas flexible conduit may be had in lengths of 25 to 250 ft (7.6 to 76.2 m), depending on the size of the conduit. The rules governing the insulation on the wires are the same as for rigid conduit: outlet or switch boxes must be installed at all outlets or switches, and the conduit must be continuous from outlet to outlet and be securely fastened to the boxes.
Terrell Croft; Frederic P. Hartwell; Wilford I. Summers: American Electricians' Handbook, Sixteenth Edition. FLEXIBLE-METAL-CONDUIT WIRING, Chapter (McGraw-Hill Professional, 2013), AccessEngineering