A method for monitoring a ground resistance (R PE) of an electric installation which consists of an ungrounded stationary alternating-voltage power supply system having at least one active conductor (L1, L2, L3) and of a consumer connected to the stationary alternating-voltage power supply system via a supply line, the ungrounded stationary alternating-voltage power supply system being supplied by a power transformer and the consumer comprising a leakage capacitor (Ce) connected to a protective conductor, the method comprising the following steps: generating a measuring signal (Us) having a measuring frequency by means of a measuring-signal generator, capacitively coupling the measuring signal (Us) in the stationary alternating-voltage power supply system between the active conductor (L1, L2, L3) and ground via a coupling circuit having a coupling capacitor (C s) and having a series resistance (R shunt), measuring a complex-valued first measuring current (I m0) in the coupling circuit when the consumer is switched off, detecting a complex-valued first measuring voltage (U m0) between the active conductor (L1, L2, L3) and ground when the consumer is switched off, determining a first complex-valued conductance value (Y m0) from the first measuring current (I m0) and the first measuring voltage (U m0), measuring a second complex-valued measuring current (I m1) in the coupling path when the consumer is switched on, measuring a second complex-valued measuring voltage (U m1) between the active conductor (L1, L2, L3) and ground when the consumer is switched on, determining a second complex-valued conductance value (Y m1) from the second measuring current (I m1) and the second measuring voltage (U m1), computing a complex-valued load-side conductance value (Y v) by forming a difference between the second conductance value (Y m1) and the first conductance value (Y m0), computing a complex-valued load-side impedance (Z v) from the inverse of the load-side conductance value (Y v), computing a sum ground resistance (R' PE) by subtracting the series resistance (R shunt) and loss resistances (R ESR) of the leakage capacitor (Ce) and the coupling capacitor (C a) from the real part of the complex-valued load-side impedance (Z v), generating an alarm signal if the sum ground resistance (R' PE) exceeds a ground resistance threshold (R PElim). generating a measuring signal (Us) having a measuring frequency by means of a measuring-signal generator, capacitively coupling the measuring signal (Us) in the stationary alternating-voltage power supply system between the active conductor (L1, L2, L3) and ground via a coupling circuit having a coupling capacitor (C s) and having a series resistance (R shunt), measuring a complex-valued first measuring current (I m0) in the coupling circuit when the consumer is switched off, detecting a complex-valued first measuring voltage (U m0) between the active conductor (L1, L2, L3) and ground when the consumer is switched off, determining a first complex-valued conductance value (Y m0) from the first measuring current (I m0) and the first measuring voltage (U m0), measuring a second complex-valued measuring current (I m1) in the coupling path when the consumer is switched on, measuring a second complex-valued measuring voltage (U m1) between the active conductor (L1, L2, L3) and ground when the consumer is switched on, determining a second complex-valued conductance value (Y m1) from the second measuring current (I m1) and the second measuring voltage (U m1), computing a complex-valued load-side conductance value (Y v) by forming a difference between the second conductance value (Y m1) and the first conductance value (Y m0), computing a complex-valued load-side impedance (Z v) from the inverse of the load-side conductance value (Y v), computing a sum ground resistance (R' PE) by subtracting the series resistance (R shunt) and loss resistances (R ESR) of the leakage capacitor (Ce) and the coupling capacitor (C a) from the real part of the complex-valued load-side impedance (Z v), generating an alarm signal if the sum ground resistance (R' PE) exceeds a ground resistance threshold (R PElim).