MAINTENANCE OF CONTROLS, INSTRUMENTS, AND SWITCHGEAR
SECTION I. ANNUNCIATOR ALARM SYSTEM
10-1. GENERAL. The annunciator alarm system consists of annunciator relay panels A10 and All, the annunciator
panel A9, alarm horn LS1, and related parts. Fourteen fault sensors are located throughout the generator set. Each
sensor opens or doses a switch if a fault occurs, energizing one of 18 alarm relays on annunciator relay panel Al0 or Al1.
Four unused relays on annunciator relay panel All provide for installation of additional fault sensors or for use as spares if
any of the original 1 4 relays and related circuits should fail. The following subparagraphs describe the operation of
atypical annunciator alarm system circuit.
Fault Sensor. Refer to Figure 10-1. Lubricant temperature switch OT2 is a typical fault sensor. Upon an over
temperature condition, OT2 will dose. The dosing action of OT2 connects positive dc voltage to alarm relay Al
OK4, energizing the relay.
Alarm System Self-Latching Relays. Refer to Figure 10-1. Alarm relay Al OK4 is a typical annunciator alarm
system self-latching relay. Whenever energized by the single fault sensor connected to it, self-latching contacts
dose to ensure the relay remains energized, even if the switch in the fault sensor reopens. Once energized, K4
will remain latched until manually deenergized as described in step f, below.
Alarm Relay K26. Refer to Figure 10-1. Whenever a self-latching annunciator alarm system relay such as K4 is
energized, alarm relay K26 is energized through the latching contacts of the alarm relay (K4). The contacts of
alarm relay K26 dose to apply positive dc voltage to flasher DS1 9 and, through the normally dosed contacts of
alarm silence relay K25, to horn LS1. The horn sounds.
Flasher DS1 9 and Annunciator Panel A9. Refer to Figure 10-1. Flasher DS1 9 operates at three cycles per
second and has a 50 percent duty cycle. Three times per second, flasher relay K24 is energized through flasher
DS1 9. Each time K24 is energized, annunciator display light A9D7 is illuminated to provide a visual indication
of which fault circuit has tripped the alarm system. Annunciator display light A9D7 is just one of 18 lights in
annunciator panel A9. Fourteen of the lights are each associated with one of the 14 fault sensors in the
generator set. The remaining four lights are associated with the four unused alarm circuits in the system.
Alarm Silence Relay K25. Refer to Figure 10-1. Horn LS1 will continue to sound until ALARM SILENCE
pushbutton S16 is manually pressed to energize sell-latching alarm silence relay K25. When relay K25 is
energized, its normally closed contacts open, cutting off positive dc voltage from horn LS1. The horn goes dead.
Simultaneously, the normally open contacts of relay K25 dose to connect flasher relay K24 directly to positive
DC voltage, bypassing flasher DS19. Relay K24, which had been receiving positive dc voltage on and off, three
times per second, is now continuously energized. As a result, annunciator display light A9DS4, which had been
flashing, is now continuously on.
ANNUNCIATOR RESET Pushbutton 12A. Refer to Figure 1 0-1. Annunciator display light A9DS4 will remain on
until the annunciator alarm system circuit has been reset via ANNUNCIATOR RESET pushbutton SI 2A When
pushbutton S1 2A is pressed, the following occurs:
Positive dc voltage is disconnected from self-latching annunciator alarm system relay Al OK4. The relay
deenergizes and unlatches. Annunciator display light A9DS4, which has been receiving battery positive
through the latching contacts of Al OK4, goes out.
Alarm relay K26 deenergizes when the latching contacts of Al OK4 open. The normally open contacts of
K26 open to disconnect battery positive from flasher DS19 and flasher relay K24.
Pressing pushbutton S1 2A also disconnects battery positive from self-latching alarm silence relay K25.
Relay K25 deenergizes and its normally closed contacts reset the horn circuit. The normally open contacts
of K25 open to reset the flasher circuit.
ANNUNCIATOR TEST Pushbutton S15. Refer to Figure 10-1. ANNUNCIATOR TEST pushbutton SS is used to
check annunciator alarm system lights and horn operation. The pushbutton is designed to be used in the
absence of a true alarm and works as follows: (1) Pressing pushbutton S15 connects battery positive to horn
LS1. The horn will sound as long as the pushbutton is pressed.