This section is from the book "A Treatise On Architecture And Building Construction Vol3: Stair Building, Ornamental Ironwork, Roofing, Sheet-Metal Work, Electric-Light Wiring And Bellwork", by The Colliery Engineer Co.. Also available from Amazon: A Treatise On Architecture And Building Construction.
85. A simple bell circuit is shown in Fig. 63. A battery of two Leclanche cells c, c connected in series furnishes current to the bell b, located at any part of the house, and the push button p is placed at any convenient point.
86. It is frequently necessary to ring two or more bells from one push button. This may be accomplished by one of two methods. One is to connect the bells in multiple arc across the leads, as in Fig. 64, so that each one is independent of the others, the bells a, b being on separate circuits. The battery B is represented in this diagram in the manner generally adopted, the fine line indicating the carbon of the cell, and the heavy line the zinc. The other method, making use of a series arrangement, is shown in Fig. 65. This is often preferred to the first method, because there is usually a saving of wire in its employment, but it is necessary to change all but one of the bells to single stroke, as already explained. The reason for this is that, unless the bells were exactly similar in their adjustment, the period of vibration, or rate of swing, of the armatures would be different, and the interference would prevent satisfactory ringing of the bells. If, however, one bell is free to vibrate, and the rest are all changed to single stroke, very little adjustment to each one will be required to produce a strong, clear ring.
87. When it is desired to ring a bell from two different places, the simple circuit cannot be used, because there would be a break at each push button, and a current would not flow unless both buttons were pressed at once. The second button must then be in parallel to the first, as in Fig. 66, so that whichever button p or p' is pressed, the circuit through the bell b and battery B is completed.
88. Figs. 67 and 68 show two arrangements of wiring for ringing two bells simultaneously from three different points. The bells a, b are connected in multiple arc (or parallel) in Fig. 67, but they may be put in series, if desired, as in Fig. 68, provided one of them is changed to single stroke. In the case of an actual installation, it might be necessary to run the wires in some other manner than as here laid out, depending upon the construction of the building; but, from the directions already given, it should be an easy matter to devise the best arrangement. The choice between series and parallel connection of the bells will depend upon which is more economical in copper for the line wires. The wire to use will be No. 14, 16, or 18 Office Wire, according to the number of bells on the circuit.
89. When two bells are arranged to ring from one push button, it is sometimes desirable to cut one of them out during some part of the day. For this purpose a small switch, Fig. 69, is used, by means of which the bell may be short circuited.
The wires are run to the back of the switch, one connection being to the lever arm at a, the other to the contact piece b.
90. The connections for the automatic drop are shown in Fig. 70. The circuit obtained, on pressing the push button p, is from the positive pole of the battery B through the push to the terminal a of the drop, through the magnet coils to terminal b, then to the negative pole of the battery by way of the bell. As soon as the drop d falls, the magnet coils are cut out, the current is diverted at e and passes by way of the new contact from terminal c to b, thence through the bell as before to the battery.