Overvoltage and overcurrent protective circuit with high earth balance

An overvoltage and overcurrent protective circuit for a terminal circuit or net terminal which has two input terminals (a, b) and a number of output terminals (T1-T4), wherein the input terminals are intended for connection to a two-wire line and the output terminals are intended for connection to equipment to be protected by the overvoltage and overcurrent protective circuit, said terminal circuit being intended for two-way transmission of digital and analogue signals over the line, comprising a line transformer (LT2) having a primary winding (L1, L2) a secondary winding (L3, L4) and a core, wherein the primary winding has two winding halves (L1, L2), a first earth-symmetrical protective circuit arranged on the primary side of the transformer and including a capacitor (C) and two current limiting resistors (Ra1, Ra2), wherein the capacitor is intended to be connected in series between the two winding halves such as to form a series combination which is connected across the input terminals (a, b), and a second earth-symmetrical protective circuit arranged at the secondary winding of the transformer and including zener diodes (Z5, Z8) for limiting the voltage across the output terminals, characterized in that the first protective circuit includes a varistor (V1) and two temperature-dependent semiconductor resistors (PTC1, PTC2), of which one resistor is connected in series between one end of the varistor and one coating of the capacitor, and the other resistor is connected in series between the other end of the varistor and the other coating of the capacitor;

• and in that the series combination is connected directly across the input terminals (a, b) in the absence of an intermediate series resistance.