528 



ELECTRICAL EQUIPMENT 



by hand and opened either by hand or by some automatic tripping 

 arrangement, a circuit-closing auxiliary switch for closing the alarm 

 circuit is so mounted on the operating mechanism that when the 

 circuit breaker is opened by the hand-closing mechanism, the aux- 

 iliary switch does not operate. But if the tripping is affected by 

 the automatic mechanism, the auxiliary switch will close and 

 throw in circuit the alarm device. 



On electrically operated circuit breakers no arrangement of a 

 mechanically operated auxiliary switch, which will allow it to 



distinguish between nonautomatic 

 and automatic opening, can be con- 

 ventionally made. Consequently, to 

 inform the operator of automatic 

 opening, there is used generally a 

 bell alarm relay with its operating 

 coil connected in the power supply of 

 the circuit-breaker tripping coils, 

 (Fig. 331). The operation of the 

 relay is not affected by the control 

 switch circuits, and is energized only 

 when -current passes through the 

 tripping circuit contacts of one or 

 more of the protective relays. 



Whenever a circuit breaker is 

 automatically tripped, the relay coil 

 is energized for an instant through 

 the circuit of the overload trip. As 

 it may be necessary to ring an alarm 

 bell for some time to attract the 

 operator's attention to the fact that 

 a device has been opened automatic- 

 ally, the relay plunger is notched so 

 that it remains up in the closed posi- 

 tion until pulled down by hand, 

 which shuts off the alarm bell by 

 opening the bell-alarm circuit. 



Control Relays. These are used in connection with the con- 

 trol switches for electrically operated oil circuit breakers, etc. 

 Since these control switches, as a rule, are not constructed to open 

 a current of sufficient capacity to operate the closing coil of the 



T FiQ. 332. Solenoid Control 

 Relay. 



