| 摘要 |
A fault current circuit apparatus for an auxiliary device connectable to telecommunications terminal devices, particularly a telephone set, in a digital telephone system is provided. In addition, signal lines for connecting electronic circuits in both devices are provided. The signal lines in the auxiliary device are connected via protective diodes to at least one ground line that carries a reference potential. A dc voltage is supplied to the auxiliary device from the telecommunications terminal device via a fault current protection circuit. In case of a fault caused by an inadmissible dc voltage potential on the ground line with reference to the signal lines, the dc voltage is shut off by the fault current protection circuit.
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