Carbon break circuit breakers.

an actual blow, the jar of which is great enough to dislodge the catch at the upper end and thus release switch L. By varying the position of i, the force exerted upon it by the solenoid can be changed so that the device can be set so as to trip with currents of different strengths. This position of i is varied by means of the screw A.

The principles illustrated in Figs. 133 and 134 are those most commonly used in the construction of commercial circuit breakers for continuous current circuits. Fig. 135 is a line drawing of a circuit breaker acting upon these principles. The solenoid coil is at B and C is the plunger, while M is the adjusting screw, by means of which the device is adjusted to trip with any desired current. When C is lifted it strikes E and thus throws up the trigger H, allowing the catch F to release G. The plunger I, which is forced outward by the spiral spring, impinges against the switch at K and throws it open, thus breaking the circuit. The switch contacts are arranged with double breakers, one being made of copper and the other of carbon. The copper contacts separate first, and the circuit is finally broken between the carbon contacts. The carbon break circuit breaker, as manufactured by the General Electric Company, Fig. 137, meets all demands for a small, reliable, automatic, protective device for direct and alternating current systems.

The operation of the circuit breaker is absolutely positive, and it can be adjusted to trip at any predetermined point between its wide limits of calibration. A fuse is inflexible in this respect; its time lag is appreciable and more or less dependent upon climatic conditions; it can never be absolutely relied upon to rupture at its rated capacity.

Through the use of a double or triple pole circuit

A good type of circuit breaker.

breaker with independently operated arms, the usual lever switch in series may be dispensed with, since such a circuit breaker performs the functions of both switch and single pole breaker. Either arm may be closed and is then free to trip, and will trip instantly in response to an overload or short circuit (should such exist) when the second arm is closed.

Circuit breakers of the type shown in Fig. 137 are suitable for every class of service requiring automatic protective devices, and are used extensively in steel mills, machine shops employing electrically driven tools, office buildings, etc. They are indispensable for general motor

Details of Working.

work, automobile charging sets, cranes, and electrically driven machinery in general.

The laminated brush is a feature of this circuit breaker. In closing the breaker a rubbing motion is imparted to the brushes which insures clear contacts.

The circuit is finally broken and the arc ruptured by

Figure 138. General Electric Co.'s circuit breaker.

means of carbon contacts of simple construction securely fastened to metal arms. The carbon blocks may be quickly and easily replaced if burned.

Extreme ease of operation is secured by the use of a toggle movement, and the breaker will not jar out, nor will it open unless purposely tripped by hand or actuated by the automatic tripping device in the event of an overload or short circuit.

The tripping point may be varied by adjusting the air

Another type circuit breaker.

gap between the electro-magnet (overload coil) and its armature. With the exception of those in the underload circuit breaker, no springs are used in the tripping device, the force on the armature being opposed to gravity. The trip is positive, the pull on the armature increasing as the air gap decreases, consequently when the armature begins to rise it will continue to do so with increased force until

the breaker trips. With this construction any danger from "creeping loads" is obviated.

Two other types are shown in Figs. 138 and 139.

It will be noticed that in this circuit breaker each switch blade is held by an independent catch; on this account it can be used as a main switch at the same time that it acts as a circuit breaker.

Why this is the case will be understood from the following: A circuit breaker may act because the current