New building wires recognized by 1940 code

The 1940 edition of the National Electrical Code recognizes 19 different types of building wire. Only 7 of these are rubber-covered building wires, yet when an electrical engineer thinks of building wire he almost instinctively calls to mind rubber-covered wire. This is because rubber insulation has been so generally satisfactory that it is produced and used in a volume vastly in excess of all the other types of wires combined. Within its temperature and voltage limits it has no peer. Most of this article therefore will be devoted to rubber-covered wires, although other types will be mentioned briefly.