Improvements in Electric Fire Alarum Contact Makers

3860. Hislop, R. G. March 11. Retractive switches. - In fire-alarm switches of the type in which a circuit is automatically completed by breaking the glass in the lid of the switch-box, a lever i controlled by a pushbutton o is provided in order that the lid may be opened without operating the switch. The spring e normally tends to raise the plunger a and contact plate b to close the circuit; but when the lid is open, this movement is prevented by the lever i, one end of which engages the contact plate b, while the other end engages the push-button o, the spring p of which overpowers the spring e. A false alarm may be given for purposes of fire-drill in schools or other institutions by depressing the push-button o when the lid is open. When the lid is closed, the framework of the lid presses down the push-button o and relieves the pressure of the lever on the contact plate b, so that the plunger a can rise to complete the circuit when the glass is broken.