Circuit, External. A portion of the circuit not included within the generator, such as a secondary telegraph key and sounder.
Circuit, Grounded. A circuit in which the ground is used as a conductor. This is common in telegraph and telephone lines, particularly for short distances where the conductivity of the earth does not offer too much resistance.
Circuit, Incandescent. A circuit in which incandescent lamps are installed.
Circuit Indicator. A pocket-compass, galvanometer, or other device for indicating or detecting the condition of a wire, whether it is active or dead, and, if active, in which direction the current is flowing. It may also give a general idea of its strength.
Circuit, Internal. That portion of an electric circuit which is included within the generator.
Circuit Loop. A minor circuit introduced, in series, into another circuit by a switch or cut-out, so that it becomes a part of the main circuit.
Circuit, Main. a circuit or main line, includes the apparatus supplying current to it. Thus distinguished from a local circuit.
Circuit, Metallic. A circuit in which the current outside the generator passes through metal parts or wire, but not through the ground. Electric light and power lines are always metallic circuits. An electro-plating apparatus may be properly termed a metallic circuit, although a part of the circuit is formed by the electrolyte in the bath. The essential meaning of the words metallic circuit is that the earth does not form a part of the return circuit.
Circuit, Open. A circuit in which a switch has been opened to prevent the continuous flow of current, such as an electric-bell circuit, which normally remains open, and which is active only when the push-button is pressed, thereby closing the circuit and operating the bell. An open-circuit battery is one that remains inactive when the circuit is open.
Circuit, Parallel. A term signifying a multiple circuit.