Figs. 226-229.
[Fig. 230] is designed to illustrate the front of a continuous current two wire switchboard with circuit breakers; these are made up usually of marble or slate so that they will not burn; the Insurance Underwriters require a non-combustible material at this place, as well as hangers, and insulators used for conductors.
The Switches shown in the middle of the board, are enlarged in [Fig. 232], and are used for closing the connections with the generators and lines running to various parts of the field to be lighted or furnished with power.
The switch handles are made usually of wood or hard rubber; the blades are of copper. The connections are soldered into the sockets shown upon the ends of the screws which project beyond the back of the switch-board.
The upper row of figures as shown in [Fig. 230] and enlarged in the engraving, [231], are circuit-breakers. The use of these is analogous to that of the safety-valve upon a steam boiler, so that when the pressure in the circuit exceeds that at which it is set the “breaker” opens the circuit and thus prevents damage.
Fig. 230.
In this case, the main contact is formed by means of a laminated brush while the final stroke is made on carbon, the motion of this breaker is by means of a toggle-joint which so multiplies the power applied that it does not require much of an effort to close it; this device maintains the same speed in operating the breakers when the circuit-breaker is tripped.