104123 MAR 1 8 1907 TOL 6933574 Switchboards In a very small, isolated plant, where a single generator is used, the current can be conveyed to the apparatus in which it is utilized in a comparatively crude manner; all, in fact, that is required being suitable conducting wires to complete electric circuit. If there are several generators, feeding into a more or less complicated network of distributing wires, the circuit connections will become complicated unless a systematic way of arranging them is resorted to. There will be considerable complication even if only one generator is used, providing the distributing system is complicated. To simplify the arrangement of the wiring, the best course of procedure is to run the wires leading from the generator, or generators, to a central point, and then from there branch out to the various distributing circuits. This central point to which the generator wires are run, and from which the circuit wires start, is called a switchboard. The general arrangement of a switchboard depends very largely upon the service it is to perform, and also upon the type of current it is to handle. For continuous currents we have the constant potential and the constant current systems, and each one requires a switchboard arranged in a decidedly different manner. For the alternating current systems we have the single phase and the polyphase, both being of the constant potential type. Constant current alternating currents are very seldom Before switchboards were used. used, except for "arc" lighting. As the continuous current systems are the most simple we will start the discussion with these, taking up first the constant potential switchboard. The switchboard, in the strictest sense of the word, is not an indispensable adjunct of an electrical installation, and in fact was unknown for several years after the introduction of electric lighting. It first came into use, in a very crude form, as a matter of convenience; it was gradually elaborated, and at the present time is regarded as a part of the system only second in importance to the generator itself. It belongs to that vast class of apparatus that first come into use as a luxury and finally come to be regarded as a necessity. At the present time we would consider it impossible to operate a boiler without a steam gauge, but they were so used in days gone by, and if we had no gauge we could get along without it. These remarks are equally applicable to the electrical switchboard. In the early days of "arc" lighting the wires from the binding posts of the dynamo were run directly out to the lamp circuit, in most cases not even a switch being used. Whenever it became necessary to discontinue the lights, the dynamo was stopped. Before long it became evident that a switch introduced into the circuit would be a convenience, as then it would be possible to put out the lights without stopping the dynamo, and this certainly would be advantageous in cases where it was desired to suspend the lights for only a few minutes. In this way the switch for opening the line came into use. Very early in the history of "arc" lighting it was discovered that unless the current remained practically uniform, the Voltmeter and ammeter. lamps would not burn steadily; hence it became desirable to have an instrument whereby the current strength could be indicated, and this brought into use the ammeter. With incandescent lighting it was soon found that uniformity. of pressure was the point of vital importance, and thus the voltmeter was introduced in such installations. In "arc" lighting the current remains of constant strength, therefore there is no danger of burning out the generator by overloading. In the incandescent lighting system the case is different; each lamp adds its quota to the current strength required, and if the number of lamps is sufficiently increased, the current will become strong enough to burn out the generator, providing there is enough power behind it to keep it running. To prevent burning out generators of the incandescent type, by overloading, safety devices were gotten up; these acting by opening the circuit and thus stopping the flow of current whenever the danger limit is reached. There are two types of safety devices used to avoid the destructive effects of overloads; one is the "safety fuse," which is simply a piece of wire of such size that it will be melted by a current of sufficient strength to injure the generator, and the other is the "circuit breaker," which is actuated by a magnet, the strength of which is exerted in opposition to a spring or some other counteracting force. strength of the magnet increases with the current, and when the predetermined point is reached, the device acts, as at that point the force of the magnet is sufficient to overcome the reactive force. Generators used for incandescent lighting are designed to develop the required pressure at a certain velocity of rotation, but it frequently happens that for one reason |