metallic circuit

metallic circuit

[mə′tal·ik ′sər·kət]
(electricity)
Wire circuit of which the ground or earth forms no part.
References in classic literature ?
In this period came the multiple switchboard, copper wire, girl operators, underground cables, metallic circuit, common battery, and the long-distance lines.
Patchfinder features an integral metallic circuit that connects LED indicators on each end of a premium-grade fiber jumper.
Essentially, three types of telephone lines are used to transmit burglar alarm signals: metallic circuits, voice-grade lines, and a switched network.
Metallic circuits are pairs of copper wires that connect the protected premises directly to the central station.
Voice-grade lines are similar to metallic circuits in that they are leased from the telephone company and dedicated to alarm signal transmission.