Base element for accommodating an overvoltage protection module, and modular bus system

The invention relates to a base element (ST1, ST2, ST3) for receiving an overvoltage protective module (M1, M2, M3) for use in a bus system, having a first bus connection arrangement (BK1) for contacting a first bus potential (L1), a second bus connection arrangement (BK2) for contacting a second bus potential (L2), a third bus connection arrangement (BK3) for contacting a signal bus (L3), wherein the signal bus in a first state indicates the occurrence of a fault and in a second state indicates the non-occurrence of a fault, wherein a fault indicates a missing or incorrectly received or faulty overvoltage protective module (M1, M2, M3), wherein the first and second bus potential are to be used to supply arrangements on the overvoltage protective module (M1, M2, M3), wherein the base element further comprises an electronic monitoring arrangement (UE1), wherein the electronic monitoring arrangement (UE1) identifies whether an overvoltage protective module (M1, M2, M3) is received, wherein, if an overvoltage protective module (M1, M2, M3) is received in the base element (ST1, ST2, ST3), the second state is signalled via the signal bus, and, if no overvoltage protective module (M1, M2, M3) is received in the base element (ST1, ST2, ST3) or if the overvoltage protective module (M1, M2, M3) is received incorrectly or if the overvoltage protective module (M1, M2, M3) is faulty, the state of the signal bus remains unchanged, wherein the base elements (ST1, ST2, ST3) can be clipped onto a mounting rail (TS1, TS2), and the first bus potential (L1), the second bus potential (L2) and the signal bus (L3) are guided in a recess in the mounting rail (TS1, TS2).