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almost every case the connections with the ammeter, voltmeter, and other instruments are made with cables or
wires. It will also be noted, in Fig. 42, that there are five circuit breakers in the middle panel, one for each
Switches for distribution.
machine, and that in the side panels there are as many circuit breakers as there are switches, showing that each one of the distributing circuits is provided with a circuit breaker.
Figure 46 Another form of heavy conductors. Fig. 43 shows the back of the switchboard, Fig. 44. In this board, the switches that make the connections with the distributing circuits, are arranged in vertical rows at the side, and as will be seen in the back view, Fig. 43, the circuit wires are run directly from the switch terminals, and are led off at an angle so as to clear each other. The connections from the generators come up through the floor. It will be noticed, in Fig. 44, that
there are four instruments at the bottom of the board of rectangular outline with cylindrical fronts. These are integrating wattmeters, and are for the electric system what gas meters are for gas systems, that is, they measure the amount of electrical energy that passes through them. One of these meters is connected in the circuit of each generator, and thus the output of each machine can be
read and compared, and by adding the readings of the four instruments the total output of the plant can be ascertained.
When the capacity of a system is large and the e. m. f. rather low, or even if the capacity is moderate, if the e. m. f. is very low, the strength of the current becomes so great, that it taxes the ingenuity of the designer to
Allow access to back of board.
provide room enough at the back of the board for the conductor bars without making the dimensions of the board much larger than they need be for the accommodation of the switches and other devices. As an illustration of such cases is shown Fig. 45, which is the back of a board used in a manufacturing establishment where the e. m. f. is very low, and the current strength runs
up into several thousand amperes. As will be seen, all the connections are of a massive kind, and there is very little waste room between the conducting bars. Another example of a somewhat different design is shown in Fig. 46.
It has already been stated that the switchboard should be set far enough from the wall to allow free access to