为了保护电子Schnitttstellenschaltung（SLIC），以及用于测试访问电子开关（STA1，STA2，LA，LB）是每一行线（A，B）的第一（线路侧和所述线丝测试访问或分离开关之间的La， 磅）和DT2 / RS2连接在接入交换机STA1，STB12）桥接所述第二阈元件（）的接入交换机（STA1，STB1）（针对相应线路的导线a）首先阈元件（RS1 / DT1）用于消散过电压到大地和一个（， 经由第三阈元件（DT3）及接地电位的连接。

To protect the electronic Schnitttstellenschaltung (SLIC) and of electronic switches for the test access (STa1, STa2, La, Lb) is per core (a, b) a first between the line side and a lying in the line wire test access or isolation switch (La, lb) and the access switch (STa1, STb1) for the line conductor in question (a) first threshold element (RS1 / DT1) for diverting surges to ground and an access switch (STa1, STB12) bridging second threshold element (DT2 / RS2) connected, via a third threshold element (DT3) and ground potential is connected.