GB479516A - An improvement relating to street fire alarm systems - Google Patents

Abstract

479,516. Fire - alarm systems. STELJES, W. S. May 7, 1936, No. 12876. [Class 40 (i)] In a fire-alarm system of the kind wherein signals are transmitted from street boxes over a closed line circuit under normal working conditions and over an earth return under fault conditions, an indicating device is provided in each street box and is adapted to be operated from the fire station. As shown, the street box apparatus B is connected to the fire station C over a normally closed loop circuit including relays j, j<1>, resistance h and short-circuiting contacts g, g<1> of a relay d. When the transmitting apparatus of the box B is operated contacts g, g<1> are opened, but relay d remains inoperative to the normal signal current. Upon receipt of the signal at the fire station, key i is operated to shortcircuit the resistance h and cause operation of relay d and indicator lamp f. In order to ensure correct operation when the system is working under emergency conditions, relays j, j<1> pull up to earth the line through resistances j<2> and thus prevent inadvertent operation of relay d due to the decrease of line resistance and the consequent increase of the line current. The Provisional Specification describes a system wherein the indicating lamp is directly included in the line circuit and is operated by switching into the circuit an additional battery in the fire station.