The use of electric bells on lighting circuits is becoming quite general, as it obviates the necessity of using batteries, and thereby simplifies both installation and maintenance.
There is no fundamental objection to operating make and break bells on electric light circuits. Providing the voltage and amperage are the same, there is little difference between the current from a direct-current dynamo and that from a battery. But owing to the higher voltages of the lighting circuit over that generally employed from batteries, the bell coils must be wound to high resistances to keep down the current strength. There are also other slight changes to assist in suppressing sparking, as have been already treated on.
Where the circuit is not over 220 volts, the bells are wound with fine wire and have also self-contained resistance coils. For 500 volts and over, a resistance lamp is connected in with the bell which in this case is wound for a 150-volt circuit.
These bells up to 6-inch and inclusive will operate on circuits of either direct or alternating current.
Above this size it is necessary to use specially constructed bells on alternating current circuits.
Fig. 63
Most large hotels and office buildings having direct current lighting service are using it for ringing bells and similar work to the total exclusion of batteries.
Where the number of units to be operated justifies it, motor generators are operated in connection with the lighting mains to produce a low voltage most suitable for the bells. The connections in this case are no different to those when batteries are employed.