Fig. 64.
Trolley Wire. The trolley wire is suspended from the span wires or brackets in such a way as to permit of an uninterrupted passage of an upward pressing trolley wheel underneath it. The trolley wire itself may be either round, grooved, or figure 8 in section. Where a round wire is used, No. 00 B. & S. gauge is the most common size. Figure 8 wire, so called from its section, which is shown in [Fig. 64], is designed to present a smooth under surface to the trolley wheel, which will not be interrupted by the clamps or ears used to support it. Clamps are fastened to the upper part of the figure 8. The grooved wire is rolled with grooves into which the supporting clamps fasten. This wire also presents a smooth under surface to the trolley wheel.
Fig. 65. Trolley Wire Clamp and Ear.
Trolley-Wire Clamps and Ears. The trolley is supported either by clamps or by soldered ears. One type of clamp grasps the wire by virtue of screw pressure. A soldered ear is shown at E, [Fig. 65]. This ear has small projections at each end, which are bent around the wire to assist the solder in holding the wire to the ear. Another form of ear, used to some extent, holds the wire by virtue of having the edges of the groove offset or riveted around the wire.
The ear or clamp screws to a bolt which is insulated from the metal ear through which passes the span wire. A cross-section through a common type of trolley-wire hanger is shown in [Fig. 66]. Here there is an outer shell of metal, which is adapted to hook to the span wire. In this shell is an insulating bolt, that is, a bolt surrounded with some form of insulating material which is very strong mechanically and not likely to be cracked by the hammering action of the passing trolley wheel. Most of the insulating compounds used in making trolley-wire insulators are trade secrets. Another kind of insulator called the “cap and cone” type is shown at C, [Fig. 65]. In these insulators, the metal part B which fastens to the span wire does not completely surround the insulation C. Wood has sometimes been used for the insulation of trolley-wire hangers.
Fig. 66. Cross-Section Trolley Wire Hanger.
Span Wires. In city streets, the trolley wire is commonly suspended from span wires stretched between poles located on both sides of the street. These span wires are of ¼-inch or ⅜-inch galvanized stranded steel cable. In order to add to the insulation between the trolley wire and the poles at the side of the street, what is called a strain insulator is placed in the span wire. This is an insulator adapted to withstand the great tension put upon it by the span wire. One of these is shown in [Fig. 67]. Means are usually provided for tightening the span wires as they stretch and as the poles give under the strain. The insulator in [Fig. 67] has a screw eye for that purpose.