An instance of old electrical wiring in the US with cloth-sheathed NM (nonmetallic sheathed) cable leading along a joist and into a metal box through a knockout. NM cable with cloth sheathing was used from 1930 through 1965; more modern NM cable has a sheath made of PVC material. (See "Black & Decker The Complete Guide to Wiring, 5th Edition", Creative Publishing Intl., 2011, pg. 29.)