Electric ovens are constructed to utilize electric heat in an insulated enclosure. Heat derived from electricity is more expensive than from other sources but when used in insulated ovens it may be made to conveniently perform the service of that derived from other fuels. In electric ovens the heaters are attached to inside walls. As in other heating elements they are arranged to suit the conditions for which the oven is to be used. The heaters are usually so divided as to permit either all of the heaters to be used at the same time to quickly produce a high temperature, or only a portion of the heat to be used in keeping up the temperature lost by radiation. Ovens of this kind may be provided with regulators by means of which the heat may be automatically kept at any desired temperature. Such heating and temperature regulation may be used to produce any desired condition, but in practice the cost of the heat is the factor which determines its use. Unless electric heat is conserved by insulation it cannot become a competitor with other forms of heating.
Fig. 235.—Electric three-burner hot plate. Electric hot plate.
Electric cooking stoves and ranges are made for every form of domestic and culinary service. They fulfill many purposes that may be obtained in no other way. As conveniences, the cost of heat becomes of secondary consideration and their use is constantly increasing. In Fig. 236 is an example of a time-controlled and automatically regulated electric range. In the picture is shown separately all of the heaters for the ovens and stove top. The part S shows the switches attached to the heaters of the stove top, which is raised to show the connecting wires. In the larger oven there are two heaters of 1000 watts each, and in the smaller oven one heater of 850 watts. Each heater may be controlled separately with a switch giving three regulations of heat—high, medium and low. The advantage of this arrangement lies in the fact that one can set the two heaters in the oven at different temperatures which will permit either a slow or quick heat, but when the predetermined temperature is reached the current will be automatically cut off by the circuit-breakers. Such flexibility of heat control in the ovens permits the operator to apply heat at both top and bottom for baking and roasting at just the desired temperature. This arrangement also avoids the danger of scorching food from concentration of heat, and warping utensils or the linings of the oven. All oven heaters on the automatic ranges are further controlled and mastered by the circuit-breakers.
Fig. 236.—Electric range. Showing how all parts can be removed for cleaning and replacement.
Intercommunicating Telephones.
—This form of telephone is used over short distances such as from room to room in buildings or for connecting the house with the stable, garage, etc. It is complete, in that it possesses the same features as any other telephone but the signal is an electric call-bell instead of the polarized electric bell used in commercial telephone service.
Any telephone is made to perform two functions: (1) that of a signal with which to call attention; and (2) the apparatus required to transmit spoken words. In the intercommunicating telephone or interphone, the signal is made like any call-bell and parts are similar to those described under electric signals. The bell-ringing mechanism is included in the box with the transmitting apparatus and the signal is made by pressing a push button. It is not suitable for connecting with public telephones. Telephone companies, as a rule, do not permit connection with their lines any apparatus which they do not control.