TRANSMISSION OF ELECTRICAL ENERGY 205 



251. Electrical Apparatus. Electrical apparatus work 

 includes the manufacture of all electrical machines, instru- 

 ments, and devices. This work is so varied and widely 

 differentiated that no brief description can cover it. In 

 general, however, it may be said to consist of the skilled elec- 

 trical work required in the manufacture or repair of all forms 

 of electrical apparatus, such as generators, motors, electric 

 meters, rheostats, telephones, switchboards, and testing and 

 signal apparatus. 



252. Outside and Inside Wiring. Outside wiring consists 

 of the installation of all outdoor lines, such as general elec- 

 trical power transmission lines, street lighting, telephone, 

 telegraph, and signal lines. There are two general types of 

 outside wiring: aerial, in which the wires or cables are 

 supported high in the air on poles or other suitable devices; 

 and underground, in which the wires or cables are laid in 

 conduits. 



Inside wiring consists of the installation of electric wires, 

 appliances, and fixtures for all purposes within the confines 

 of some structure. It includes such work as lighting, heat- 

 ing, power, bell, telephone, and signal installation. 



There are four general types of inside wiring: (1) open 

 work, in which the wires are exposed to view, and are mounted 

 on cleats or knobs; (2) molding work, in which the wires 

 are run in a special molding, made either of wood or metal; 

 (3) concealed work, in which the wires are run in partitions 

 and other places not exposed to view, and are insulated by 

 means of knobs and tubes; and (4) conduit and armored 

 cable work, in which the wires are run in metal pipes called 

 conduits or are protected by an integral metal coating or 

 armor. The above classification does not include all forms 



