When plans were first formulated for the lighting of the grounds of the World's Columbian Exposition, it was decided that all electric wires and conductors, not only for arc and incandescent lighting but for power transmission, police signals, fire alarm, telephones and telegraph lines should be placed underground out of danger to the public and yet be accessible. For this purpose, the electric subway was designed and constructed. The original plan was to build such a subway of solid brick, but as this was found unnecessary for temporary service and expensive, the plans were changed to a wooden framework lined with cement, plaster and concrete floors. The approved and executed projects called for a subway connecting the electrical plant in Machinery Hall with Mines and Mining, Electricity, manufacturing, Government and Fisheries buildings.
The main subway starting from Machinery Hall was 15 ft. 8 in. wide by 8 ft. 4 in. high and was divided in the center by a fireproof partition, making two divisions 6 ft. 6 in. square on the insides. This subway was run to within 50 feet of the Electricity building where, from the west division, extended two branches 8 ft. 4 in. high by 6 ft. 1 in. broad—one to Mines and Mining and the other to the Electricity building. These were so arranged that all the wires on the west wall turned west to Mines and Mining, and those on the east wall were run directly into the Electricity building without crossing. The east division at the 50-foot point turned east to the bridge at the southwest corner of the Manufactures building, where it widened out into a fan shape the width of the bridge, and the wires were carried across on supports placed between the bridge girders. From the bridge, the subway extended 100 feet east to the western loggia of the Manufactures building, where it turned north, going the entire building length. Still, since all the wires on the east wall turned into the building at branches near the southwest corner and center, the size of the subway changed just north of the west center to a section the same size as the branch to the Mines and Mining building. At the northwest corner of the Manufactures building, the subway turned east to the north center, where it changed to a section 5 ft. 9 in. wide by 6 ft. high, reducing the capacity by one-third. From this point, it turned north, running under the Government building and across the north inlet bridge to the Fisheries building, where the subway ended. In Machinery Hall, there was a large double subway opposite the Thomson-Houston switchboard of the power plant and running 825 feet east under the south aisle, where it connected at the east entrance with the main subway and the west end with a duct trunk line. The general construction of all the subways consisted of a framework of 3 inches by 8-inches material placed 1-foot centers and covered on top, bottom and sides with 2-inch matched planking.
The inside was lined with standard metal lath and Acme cement mortar on top and sides, and the bottom was covered with 4 inches of sand and 6 inches of concrete. The cross-section of the main subway at Machinery Hall showed two bodies of wires in each of the two divisions, supported by arms projecting from the wall. These cross-arms, twelve in number, two feet two inches long, were held in position by cast iron uprights, lagged to the framework of the subway. Each cross arm supported five pins and insulators, making a total capacity of 240 insulators in a cross-section. These uprights were placed at about 30 feet apart through the entire subway and consisted of six different types, known as types 4, 6, S, 8 a, 12 and 12 a; the number indicating the number of cross arms each supported. Types 8 and 8 a, 12 and 12 a, were used around the corners. The cross arms projected into the subway 2 ft. 2 in. from either side, giving a clear passageway of 2 feet in the center. About 6,000 cross arms and 30,000 pins were used throughout the subway. For access to the subway and for convenience in pulling in wires, manholes were placed at distances of about 150 feet apart. These consisted of a round cast-iron box 20 in. in diameter and 20 in. high, resting on the framework of the subway and supplied with a cast-iron cover.
The first contract, which called for the construction of the central part of the subway, was awarded on January 23rd, 1892, to T. C. Brooks & Co., of Jackson, Michigan, for the sum of $35,094.49. Work began the first day of February 1892 and was to have been completed by April 15th, 1892. It was considerably delayed due to frozen ground and rainy weather. The bottom of the subway was only a little above datum, so considerable difficulty was experienced in putting in the concrete and flooring on account of water, but this was overcome by using a portable electrical pump. This contract did not include the subway running east and west under Machinery Hall, the portion under the Government building, the branches under Manufactures, nor the bridge approaches. This work was done by the Exposition Company, except for the plastering on the subway under the Government building, which was done by Wm. Pickland & Co., for the sum of $1,010.00. The east and west subway under Machinery Hall was difficult, chiefly because of the necessity to follow the building aisles and steam and water pipes. The total length of the subway, including the east and west subway under Machinery Hall, all the branches and approaches to the bridges, was 6,195 feet. The subway's wiring began in February 1893 and continued for about six weeks. It was found that there were so many arc wires for Manufactures building that had to be placed on the east wall of the east subway that it was necessary to run two wires on one insulator. For that purpose, a special two-wire insulator was designed and laid the glass insulation between the two wires. Wires were also arranged so that no two wires of different potential would come on the same insulator. The wiring of the subway required 4,000 of the special two-wire insulators and 20,000 of the regular single glass insulators. The subway contained 25 2-10 miles of power, 28 7-10 miles of incandescent and 51 miles of arc wires, making a total of 104 5-10 miles of wire for lighting and power transmission. Besides these were telephone and telegraph cables, fire alarms and police signal wires.
For the convenience of drainage, the profile of the floor of the subway was arranged so that all water that might collect would flow to four points, namely, north of Machinery Hall, south of the Electricity building, and west end of the north railroad bridge and north center of Manufactures building. At the bridge, an opening was made into the lagoon so the water would flow out, but marine pumps were installed at the other three places, and the water was pumped to the nearest catch basin. In this way, the subway was kept comparatively dry except on one or two occasions when a water pipe burst, completely flooding everything.
The subway was lighted with 225 110-volt 16-c.p. Edison incandescent lamps placed at distances of about 30 feet apart throughout the entire length. The lamps were placed five in series and supplied with current from the 500-volt power circuit. The lights of different circuits alternated in location so that in case one lamp burned out, it did not leave the subway in total darkness. For the convenience of keeping a meticulous record of every wire's position throughout the entire subway course, they used a card cataloging system. The cards were printed showing the exact position of all the cross arms and insulators supported by one set of uprights. Each insulator on a cross arm was numbered, and each cross arm was also numbered. On each card was marked the position of the wire on the insulator, and the circuit number of every wire, at any given point of uprights. The uprights were also numbered; a card was made for every set of cross arms and arranged consecutively in a file. By this means, it was always possible to tell the exact position of any wire at any point in the subway. Wires that ran north from the Fisheries building were carried from the subway into a duct trunk line that ran east to the Intramural railroad and thence north, following the road line around the Montana State building. This trunk line was 2,250 feet long and contained 15,270 feet of pump logs.
A clause in the contract of the Intramural railroad reserved the right for the Exposition Company to carry light and power lines along the structure underneath the roadbed on extension insulators, and lines were run this way wherever they were desired along the route of the road.
Compiled by Dr. Neil Gale, Ph.D.