Abstract: An apparatus for enabling the performance loop resistance and DC balance checks on a subscriber line includes relay contacts coupled across the line terminals. The apparatus includes circuitry for detecting the application of an activating signal to the line and for optically coupling a resulting trigger signal to a pair of monostable timers. The timer output pulses are arranged so that the relay is energized subsequent to the removal of the activating signal and remains energized during an interval established by the relative durations of the timer output pulses.

Abstract: A remote isolation apparatus includes double-position switch for selectively coupling or isolating a telephone company central office and a multi-wire subscriber line. The switch operates according to a remotely originated activating signal so that, until the switch is operated, the central office is connected to the subscriber line through normally closed contacts. When the switch is operated, the central office TIP and RING leads are coupled to a reference terminal, and the central office is isolated from the subscriber line.The apparatus includes circuitry for detecting the application of an activating signal to the line and for optically coupling a resulting trigger signal to a pair of monostable timers. The timer output pulses are arranged so that the relay is energized subsequent to the removal of the activating signal and remains energized during an interval established by the relative durations of the timer output pulses.