Chicago World's Fair — Pluto insulator

The Electric Subway on the World's Fair Grounds. - I.

BY FRED DE LAND.

When the gates of the World's Fair are formally opened there will be no overhead electric wires to mar or destroy the artistic harmony that, with two or three exceptions, prevails throughout the grounds. So, in planning the extensive electric service that will be afforded, ample ways and means had to be provided for properly taking care of wires for arc lighting, for incandescent lighting, for power circuits, and for the electric fountains; for the long distance telephone system, for the local telephone exchange and for the district messenger service; for the Western Onion telegraph and for the Postal telegraph lines; fur a police signal and a fire alarm signal; and, finally, to supply a number of subsidiary ducts for local service.

The general route of the telephone, telegraph and signal service wires was quickly planned, and pump log duct lines assigned for each class of wires. For this work over 100,000 feet of six-inch pump logs were buried where they would do the most good; in many cases two to six or eight sets of pump logs being placed in the same narrow trench that vas opened to a depth of two feet below the surface.

The next important step was the locating of the main feeders for the light and power circuits, and after thoroughly examining the scope of the work and the location of the main buildings, Mr. Frederick Sargent devised a plan, that met with approval, was adopted, and is now ready for service. One view of this subway was given in THE ELECTRICAL WORLD of July 16, 1892, but some further details of the completed subway will be of interest. Briefly it consists of a main subway, built of 2-inch tarred planking spiked to 3 x 8 inch timbers set 12 inches apart, affording an interior 6 feet 6 inches square that is rendered comparatively tire proof by a coating of cement an inch in thickness forming an artificial plaster board that is supported on expanded metal lathing. This main subway, the top of which is covered by an average depth of 20 inches of soil, commences at a point underneath the power plant in Machinery Hall, continues thereunder nearly 350 feet, and then extends north 1,075 feet to a point near the Electricity Building, where the double subway ends, one section passing 292 feet under that Building, while a branch of that section passes to and under the Mines and Mining Building, a total distance of 320 feet to the west. The other section passes 160 feet to the bridge, near the southeast corner of the Electricity Building, and has a total length of about 1,900 feet.

This subway may be likened to a long narrow shaft, but it is not a straight shaft by any means, curving around the heavy foundations and passing along a route least liable to interfere with work previously planned. In appearance it resembles a long plastered, unwhitewashed hallway, but from each wall, at the distance of every 30 feet, project one above the other out to a distance of 2 feet 3 inches twelve unpainted cross arms, each holding five locust pins that support the Pierce heavy double-petticoated glass insulators designed to hold two wires each. The cross arms are of oak, 2-1/4 x 4 inches, and are driven to the extent of 7 inches, then wedged within the sockets of upright cast iron frames that are bolted to the timbers, thus affording a strong support. In the main subway the plaster work has been so well done that no moisture has found its way through, but in the branch extending to the Mines and Mining Building the seepage will be an unpleasant feature until the new drainage system is installed. Throughout this entire length the subway is lighted by 110-volt incandescent lamps of 16 candle power, placed five in series across the power circuit carrying a 500-volt current, the lamp sockets being suspended from the ceiling to which the special glass insulators supporting these two circuit wires are attached.

The main entrance to the subway is in Machinery Hall, directly north of the space occupied by the big Westinghouse dynamos. The left hand subway leads to the Electricity Building, with a double set of cross arms, hut just before reaching that structure a narrow branch extends to the Mines and Mining Building, with one set of twelve five pin cross arms, into which entrance is secured through a trap door in the floor that is reached with the aid of a short stepladder. From the right hand subway there is no exit from the first section other than the entrance at Machinery Hall and through manholes as it terminates at the bridge, where it branches out in a "V" shaped form corresponding in width nearly to that of the bridge, under which the wires are carried from off the 24 short cross arms to 12 ten-pin cross arms that are supported between the bridge trusses in iron sockets bolted to the latter. This arrangement leaves an open but protected air space affording perfect ventilation, and also enables visitors passing under this bridge in electric launches to note the number and size of the electric conductors.

At the opposite extremity of the bridge, which is 120 feet in width, the funnel-shaped extension narrows down to the standard width of 6 feet 6 inches and extends 334 feet to the Manufactures Building, where it turns and is carried in a straight line 1,600 feet to the north beneath the portico in front of the west side of that building, then 281 feet along under the north portico and across to the United States Government Building, 421 feet under that building, and to the bridge 92 feet distant, making a total length for this second section of the main single subway of 3,808 feet. The entrances, aside from the manholes to this section of the subway are through the Manufactures Building and the Government Building, access in each case being secured through two trapdoors in the flooring of either of these buildings. As 60 wires branch off through laterals or ducts between the bridge and the centre of the Manufactures Building, front that point the number of cross-arms is reduced and those used project but front one side, while after leaving the Government building the number of wires is reduced to 40, and the subway ends at the Fisheries Building. From thence, and also from other points, wires are to be carried beneath the superstructure of the elevated electric railway. Vitrified tile 4-3/4 inches in diameter is used wherever wires enter buildings from the pump logs, the tile being curved to suit the respective cases. Over 1,500 manholes are in service, distributed at various points within the grounds.

The largest feeder wires are 0000, though the power circuits may he run up to one million circular mils built up a these wires, while the other sizes range down to No. 8 B. W. G., rubber-covered, of one-half inch outside diameter for subway and elevated structure work and of lead-covered (5/64 inch, rubber insulation inch) for pump log service.

(to be continued.)