| 摘要 |
PURPOSE:To simultaneously compensate both the maintenance of a call at the time of a power failure and an outgoing incoming/operation after the power failure by controlling the connecting operation of an exchange connection path so that the connection between a trunk line in the course of a call and a telephone set for power failure is held at the time of the power failure, and besides, at least one telephone set for the power failure is connected to the respective trunk lines. CONSTITUTION:The trunk lines 2a and 2b are connected to the speech lines 120 and 130 of an exchange switching part 10 respectively. In addition to these, the speech line 140 for an extension is provided. The telephone sets 4A-4N are connected to the lines 3A-3N respectively, and among them, the telephone sets 4A, 4B are specified to be the telephone sets for the power failure, and the exchange connection path consisting of latching relays 150, 151, and relays 152, 153 respectively controlled by a CPU 11 is formed between both the telephone sets and the speech lines 120, 130 and the speech line 140. As for the latching relays 150, 151, their contacts are held in the same state as the time of a live power, even after the occurrence of the power failure. As for the relays 152, 153, their contacts are always restored to a predetermined tilting direction (direction shown by full line) at the time of the occurrence of the power failure.
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