PLAN No. 1218. TELEPHONE COMPANIES
Telephone systems have grown phenomenally. A few years ago the telephone was a luxury. To-day it is a necessity. It has been predicted that the time will come when there will be at least one telephone in every house, just as practically every city building is now piped for water, so that it appears probable that there will be in the future a steadily increasing demand for trained telephone men.
The type of equipment used in a telephone system is determined to some extent by the size of the town or city in which the system operates. Systems serving small towns are relatively simple. The small community telephone system usually has for its lines individual wires strung on poles. There is a pair of wires for each subscriber. To call central, a hand crank on the sides of the telephone is turned which causes a shutter or drop on the switchboard to fall and expose the line number. Each line has its own drop. Thus the operator’s attention is attracted. She answers the call and by means of cords with plugs on their ends she connects the calling with the called subscriber. Such a system is called “magneto” system, because a magneto generator turned by hand crank is used for calling. Dry cells located at each subscriber’s station supply the electrical energy for talking. While a magneto system like that just described is the most desirable and economical for a small town, its application in a city would be both impractical and prohibitively expensive to operate.
Modern city telephone exchanges operate on the central-energy system. With it there are no dry cells or magnetos at the subscriber’s stations. Electrical energy for both signaling and talking is supplied by a storage battery located in the central office. For this reason an arrangement of this type is called a “central energy” or “common-battery” system. Instead of the switchboard having a drop for each subscriber’s line, it has a small incandescent lamp which is associated with the line. This lights when the subscriber removes his telephone receiver from its hook. For city telephone lines it would be infeasible to use open wires on insulators because there could not be placed on the poles a sufficient number of cross arms to support even a small proportion of the telephone lines which radiate from an exchange. Furthermore, open-line construction for city conditions would be very expensive and difficult to maintain. Hence, in the city exchanges, lead-covered cables, each containing from 20 to 1,200 pairs of conductors, are employed. Where a number of these cables are routed parallel to one another, they are carried in ducts in underground subways. In the residence sections they are supported on poles. It follows that the circuits and connections in a large city telephone exchange are exceedingly complicated. There are thousands of small wires, each of which serves a different purpose. Considered as a whole telephony involves careful work and attention to detail. Much of it is of the same order as fine instrument making.
Departments of telephone companies include: Engineering department, commercial department, auditing department, plant department, traffic department.