Abstract: The monitoring system of the conduction of a low voltage A.C. mains system comprises at least one measuring module creating a D.C. current component between two mains system conductors. The measuring module computes a value representative of the line resistance of the mains system which is proportional to the ratio between the measurement of the D.C. component of the voltage at its terminals and the measurement of the D.C. component of a voltage at the terminals of a resistor through which the D.C. current flows. An increase in this measured value indicates a loss of conduction and, therefore, such an increase is detected and indicated as soon as it exceeds a preset thereshold. A servo module delimits, may also be provided for delimiting the portion of the mains system to be monitored enabling looping of the D.C. current component and regulating the D.C. component of the voltage at its terminals to zero.