How to Install Electric Bells, Annunciators, and Alarms. / Including Batteries, Wires and Wiring, Circuits, Pushes, Bells, Burglar Alarms, High and Low Water Alarms, Fire Alarms, Thermostats, Annunciators, and the Location and Remedying of Troubles

by Norman H. Schneider

A three-point push has three contact springs. One is movable by means of the button, one is below the movable spring, and the third is above it.

Fig. 20

When the push button is not being depressed, the movable spring makes contact with the upper spring. But when the button is depressed, these two springs part, and the movable spring makes contact with the lower one.

This style of push is used for special bell and annunciator work, as will be described later.

The form of combination floor and table push in [Fig. 20] is the most solidly constructed device of its kind. The lower part is set in a hole bored in the flooring, the metal flange keeping it in place and preventing its slipping through.

The floor push attachment works as follows: The central metal rod is divided into two parts B D, by an insulating piece of hard rubber. When depressed against the action of the spiral spring by the foot, the upper part B connects together the contact springs A C, closing the circuit of bell and battery. These contact springs are insulated from each other by a hard rubber block R.

From the table push a cord containing two insulated wires leads to the two parts of the rod at B and D. When the push centre is pressed down, the push springs come together and practically short circuit B and D, which completes the circuit of bell and battery. At any time the centre rod may be removed, leaving a surface almost flush with the carpet, or floor, over which furniture may be moved without injury to the mechanism of the push.

For a floor push alone a shorter form of the centre rod is also sometimes furnished which is not divided by insulation. The spiral spring keeps it clear of the lower contact A but enables it to always make connection with the upper contact B. Pressing this rod down will also short circuit the bell and battery so that the signal is given.

A door pull attachment, like [Fig. 21], is made so that the ordinary form of lever pull bell may be changed into an electric bell. Being screwed up near the door pull, a wire is run from the latter and fastened to lever L. When the pull is drawn out the lever L turns on a pivot and a projection presses the insulated spring S against the metal base B. The circuit of the bell and battery being thus closed, the bell rings.