86 UNITED STATES NATIONAL MUSEUM 



current received at the generator switchboard as is conveyed to the 

 older buildings or is used for driving machinery throughout the new 

 building, including the elevators and fans, is transmitted directly 

 from this switchboard. All other current passes to the distribution 

 switchboard. 



The main distribution switchboard, which is situated in front of 

 the west wall of the east wing, north of the passageway into the 

 pavilion, receives from the generator switchboard eight cables of 

 500,000 circular mils, eight of 600,000 circular mils, nineteen No. 2-0, 

 and four No, 2 lead-covered cables. This switchboard is composed 

 of twenty-four marble panels — ^twelve for ceiling outlets, ten for floor 

 and wall outlets and two for the rotunda lighting — with twelve 

 switches of 50 ampere capacity on each panel. The switches are 

 arranged in four lines, in the order of the several stories, the lowest 

 representing the ground story; the next, the first story; the third, 

 the second story ; and the upper, the third story. From these switches 

 current is carried to distribution panels throughout the building, and 

 thence to the outlets in the ceilings, walls and floors, for the attach- 

 ment of lamps and incidentally of desk fans. 



Omitting the rotunda, there are in all 213 of the distribution 

 panels, each of which is contained in a sheet iron box with steel door 

 and trim. As a rule, they are placed in pairs set in the walls of each 

 story, one furnishing current to the nearby ceiling lights, the other 

 to the floor and wall receptacle outlets in the adjacent space. The 

 panels for the ceilings have each eleven, and the others 10 switches, of 

 30 ampere capacity. The connection between the distribution switch- 

 board and the panels is made by means of triple conductor cambric 

 insulated lead-covered cables, which are carried through the tunnels 

 under the basement floor in terra cotta conduits, and thence, through 

 2^-inch galvanized iron conduits, up such of the pier chases as pass 

 close to the jDanels. One such cable runs from each switch on the 

 board to one of the panels, where it is connected to the three bus 

 bars of the panel, and the switches are so connected that five furnish 

 current between the neutral and positive, while the other five furnish 

 current between the neutral and negative wires. In this way the 

 system is balanced when all the switches are thrown in with approxi- 

 mately no current passing through the neutral wire. 



Distribution of wires cmd outlets. — For carrying the wires from 

 the panels to the receptacle outlets |-inch galvanized iron conduits 

 have been used. They are covered into the construction of the floors 

 and walls and are therefore inaccessible, so, to provide for the 

 insertion or replacement of wires, pull or junction boxes are inter- 

 posed, being located in the floor, one underneath each distribution 

 panel. The tops of these boxes consist of a brass floor flange in 

 which a brass cover plate is secured by means of bayonet lugs pro- 



