| 摘要 |
A lockout circuit for connection in a telephone switching exchange utilizes a lockout relay to isolate a telephone line from common switching equipment in the exchange whenever a telephone receiver and/or the connected telephone line form a closed loop path and no attempt is made to complete a call within a prescribed period. Removal of the ground connection to the sleeve lead by the conventional timer in the trunk circuit energizes an operate winding of the lockout relay. The relay also has a hold winding connected through a set of its own contacts and the subscriber's line, and remains held up so long as the line loop remains closed.
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