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Boards for multiple circuits.

each generator were connected with the same circuit at all times, but such is not the case in practice; for one reason or another the machines are frequently shifted from one circuit to another, so that machine No. I may be connected with circuit No. I one day and with circuit

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No. 20 the next day; hence, an arc light switchboard should be so arranged that any machine may be connected with any circuit, with the least amount of trouble and the least liability to create confusion in the connections, or to produce grounds, short circuits or cross connections.

The sockets on switchboards of the type illustrated in

Plugs for arc Switchboards.

Figs. 50 and 51, are made in various forms, and this is also true of the plugs that form the terminals of the connecting cables. In every case, however, the parts are arranged so that when brought together a good and

Figure 56

The Derry Collard Co.

Figure 55

permanent electrical connection is made, and some kind of catch or retaining device is attached to either the plug or the socket to hold the two together firmly, which can be easily disengaged when it is desired to remove the plug, by simply turning the latter around its axis, by lifting or depressing or by giving it a side movement.

By an elaboration of the principle of construction employed in Fig. 51 a switchboard can be made so that all possible combinations of machine and circuit connections can be effected without the use of cables. As can be readily understood, such a modification will greatly simplify boards arranged to control a large number of circuits, and it is the construction that is used at the present time in almost every case.

From an examination of Fig. 51 it can be seen that if vertical bars are placed a few inches back of the horizontal bars in line with the vertical rows of sockets, any one of the bars of one set can be connected with any one of the bars of the other set by inserting in the proper

Arc light Switchboards.

socket a connecting plug long enough to reach through to ⚫ the vertical bars, and provided with arrangements to make contact with both sets of bars. This is the construction used in switchboards in which cables are dispensed with. Fig. 52 shows a board of this type. In the details of construction, however, a considerable difference can be found between boards made by the various manufacturers. The switchboard, Fig. 52, is the type made by the General Electric Company, and the actual construction can be made clear by the aid of the line drawings, Figs. 53 and 54, which show the front and back of a single panel arranged for three circuits and three machines. The machines are connected with one end of the vertical bars, and the lamp circuits with the other ends. It makes no difference which end the machines are connected with, whether the top or the bottom. With plugs inserted in the socket as shown in Fig. 53, the vertical bars are connected from top to bottom, so that top A is connected with bottom A, top B with bottom B, and so on for the other bars. If the plugs in the row IO are taken out the three circuits will be opened, each one at two points, as can be clearly seen from Fig. 54, if it is understood that the tubes connecting the vertical and horizontal bars are made of insulating material. The circuits will also be opened if the plugs in row 2 or row 6 are removed. When all the plugs are removed, each side of each circuit is opened at three points. Owing to the fact that the vertical bars are disconnected at lines 2, 6 and 10, it is possible to connect the lower end of one pair of bars with the upper end of another pair by simply inserting plugs in the proper sockets on lines 3, 4, 5, 7, 8, 9. To illustrate the

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