'Diagrams of switches.

former design is that the swiveling point is transferred from the end to the center of the switch blade. With this construction it would be easy for the blade to be raised from b by a downward pressure of the hand of the operator, and to avoid any trouble from such an occurrence the spring f is provided. This spring serves to hold the

blade down, as f and b are electrically connected, therefore the current would pass from S to f and thus to b.

In Fig. 90 is shown a switch that can be used for two purposes, one to connect one terminal of a line with two wires, and the other to open or close the circuit at two points at the same time. If the center stud a is connected with one terminal of the line, and b b are connected with separate wires, then it can be readily seen that when the switch blade is moved to the closed position as shown in the figure, the current entering through the wire connected with a will divide and pass out through two wires connected with b and the other with b1. If one

Multiple switches.

end of the line wire is connected with b and the other with b1, then if the switch blade is moved in the direction of arrows C, there will be a break in the circuit between S

and b and another one between S and b1, hence the two points in the circuit will be opened at the same time.

Diagram Fig. 91 represents what is called a singlethrow, single-break switch.

Diagram Fig. 92 represents a single-throw, doublebreak switch, and it will be noticed that the difference between it and Fig. 91 is, that S is not pivoted at a, hence when it is in the open position S is entirely disconnected from the circuit. When S is lowered it connects a with b, and when it is raised from this position, two breaks are

Double throw switches.

made in the circuit, one between S and a and one be

Diagram Fig. 93 shows a double-throw, singlebreak switch and diagram Fig. 94 is a double-throw, double-break switch. In these two figures it will be seen that if S is moved in the direction of arrow e, wire P will be connected with wire N; and if it is moved in the direction of arrow f, P will be connected with N1; hence there are two directions in which the switch can be moved to close the circuit.

Diagram Fig 95 shows a multi-throw, single-break switch, and diagram Fig. 96 is a multi-throw, doublebreak switch. In the first figure the wire P can be connected with any one of the six wires leading off from contacts b, c, d, e, f, g, by the movement of S, but in each case the circuit is only opened at one point.

In Fig. 96, however, wire P connects with all the contacts of the inner circle, these being joined by the ring R, and S is not directly connected with P, hence when it is moved so as to connect any two contacts it closes the circuit at two points, just as in the case of Fig. 92.

The switches so far explained are of the single pole type—that is, they open or close the circuit at one place only. The wire P, in these diagrams may be considered as one of the leads coming from the generator.

Single and double throw switches.

In Fig. 97 to 100 switches of the two pole type are shown.

The switches used on switchboards are almost invariably of the type known as knife switches. They are given this name from the fact that the blade moves in a plane perpendicular to the switchboards surface, like a meat shaver. Switches in which the blade moves in a plane parallel with the surface of the board are occasionally employed, when it is desired to connect one terminal

Figure 104.

Figures 101-104. Different types of switches.

with any one of three or more other terminals. Switches of this latter type are designated as side-throw switches. The appearance of a simple knife switch, seen from the side, is shown in Fig. 101, in which S represents the switch blade, A and N the terminals, M the switchboard surface, and f g the studs by means of which the terminals are secured in place and are connected with the conductor bars, back of the board.