| 摘要 |
PROBLEM TO BE SOLVED: To provide a switchboard adequate to an anti-lightning and anti-noise measure. SOLUTION: When a lighting surge comes in from a communication line 20, a voltage applied to a grounding electrode 13A at the contact of a PNPN lightning-protecting element 15 and the communication line is raised by the inductance of a common-mode choke coil 16 20 before the surge current becomes so large as to destroy apparatus in a building. Thereby, the PNPN lightning- protecting element 15 woks (brought into conduction) at high speed. Furthermore, a current-control element in a subscriber's protector 13 controls an increase of a current before such a large current that may destroy the PNPN lightning-protection element 15 is made to flow. Then, a gas-filled lightning conductor in the subscriber's protector 13 works (brought into conduction).
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