Interior Fire Alarm System.
Another system suitable more particularly for indoor operation is illustrated in [Fig. 69]. Here the alarm is given by breaking the glass front of an alarm box and releasing or pressing an electrical contact.
The box sounded indicates by causing a drop to fall on an annunciator and at the same time rings an alarm bell. The latter are generally provided with constant ring attachments, which keep the bell sounding until shut off.
The annunciator shown in the diagram has switches for controlling each individual bell circuit, and also for control of the entire system.
There is no practical limit to the number of stations in this system, it being determined by the size of the annunciator used or by other obvious factors.
The reference letters on the diagram are as follows: A, alarm bells which may be located wherever desired. B, break-glass alarm boxes also located at convenient points. C, annunciator drops, D, switches on annunciator which control each individual bell circuit, enabling any circuit to be cut out, cut in or tested without disturbing any other circuit. E is a general alarm switch, causing all bells to ring at once when it is operated.
The battery F varies with the number of bells and boxes and the length of line, from three cells upwards. A cut-out switch H is added to cut out the entire system by opening the battery wire. The annunciator bell is at I, an auxiliary bell being added in multiple with it when necessary.
Fig. 69
Fig. 70