Holding Coil
Holding coil. The holding coil (Coil C-158) is bridged across the line circuit when the screw switch is in the CB position and the lever switch is released. With the lever switch depressed, the coil is disconnected. If the screw switch is in the LB position, the coil is permanently disconnected, independent of the lever switch position. The purpose of this coil is to provide a low resistance d-c path through the telephone for operating the line relay and holding the supervisory relay energized on a common battery switchboard. The holding coil has high impedance to voice-frequency currents to minimize transmission losses.