Series alternating Switchboards.

rangement of voltmeters is quite common, specially with long boards. The line panels are provided with three fuses each, located at the bottom. The sockets seen at the bottom of the generator panels are for the purpose of controlling the exciter circuits. The small sockets, just below the rheostat wheels, are for connecting the voltmeter between any pair of lines. To the right of the first generator panel is seen a ground detector switch by means of which this instrument is connected with the circuits.

Switchboards for series alternating current

arc lighting.

Arc lights are operated in series by alternating currents derived from transformers provided with mechanical means to maintain the current constant. The switchboards used for this service are constructed upon the same general principle as those used with continuous currents, but, as a rule, each board is arranged to control one circuit only, although there is no difficulty in arranging the lighting and the transformer circuits so that they may be interchanged if desired. The differences between the regular arc switchboards and those used for alternating current service are simply those required on account of the difference in the nature of the currents.

The front and back, respectively, of an alternating current arc switchboard for a 35-light circuit are shown in Figs. 77 and 78. The plugs and sockets are substantially the same as those shown in Figs. 53 and 54. The only devices shown on this board that are not used on continuous current boards are two transformers, one of which

Figure 81. Wiring diagram of same.

Figures 79-80. Outline diagrams of alternating current arc light boards.

How they are made.

A re

furnishes a current to actuate the ammeter, and the other furnishes one of the currents for the wattmeter. sistance is also provided with the last-mentioned transformer, to adjust the current it delivers. The ammeter transformer is seen at the top of the board in Fig. 66, and the wattmeter transformer is located directly above the resistance used in connection with it, this resistance being located at the bottom of the board as shown in the figure. The construction of the board, and the arrangement of the circuits and various apparatus can be more fully understood from the explanatory outline drawings, Figs. 79 and 80, and the wiring diagram, Fig. 81. The location of the various devices in Fig. 61 is not the same as in Fig. 79, but as each part is clearly marked, there will be no difficulty in understanding the diagram. As will be seen, the primary current that energizes the transformer, that furnishes the current for the arc lights, runs to the two lower plugs of the switchboard, and the light circuit is connected with the two upper plugs.

The wattmeter shown in these illustrations is an instrument very rarely used in connection with continuous current arc switchboards; this, however, is not because the wattmeter is a necessary adjunct of the alternating current system, but simply because the conditions under which the current is used are such that it is desirable to measure it. In continuous current arc lighting, the switchboard and generators are located in the station, and it would be of no special benefit to provide wattmeters. With alternating series arc lighting, the transformer that furnishes the current, as well as the switchboard, may be located on the premises of the consumer, and in that case it is necessary to have a meter, so as to know what amount of current to charge for.