A method for insulation fault monitoring in unearthed electrical networks, said method comprising the following steps: - measuring an insulation resistance (8, 18) of the unearthed electrical network, - determining a responding value for the insulation resistance, - triggering a warning signal if the measured insulation resistance falls below the responding value (14, 28), - wherein the responding value is determined dynamically as a momentary responding value in a warning value establishment process downstream of the insulation resistance measurement, characterized in that - the momentary responding value is determined in the warning value establishment process as a function of a base value (R B), of setting parameters (R min, R ADY, R LIM), of ambient data and of an insulation resistance value averaged over time, and - the base value (R B) is a specific, fixed value of the insulation resistance for the network to be monitored, and - the following are used as setting parameters: a minimum responding value (R min) as a lower response limit value, an auxiliary value in the form of a responding value dynamic (R ADY) for defining a dynamic range in which the momentary responding value may change dynamically, and an auxiliary value in the form of responding value limits (R LIM) for determining a difference of the momentary responding value from the insulation resistance value averaged over time, and wherein - the momentary responding value is determined starting from the base value (R B) by a correction according to the ambient data, wherein the momentary responding value adopts the minimum responding value (R min) at its minimum and the value in the form of a responding value dynamic (R ADY) at its maximum and, within this dynamic range, lies below the insulation resistance value averaged over time, at least by the difference of the responding value limits (R LIM), and - the following influencing variables are incorporated as ambient data, either individually or in any combination, into the warning value establishment process: time, light intensity, temperature, atmospheric moisture, dew, salt content of the air, speed of change of the insulation resistance, number of people present in the region of the electrical plant, and additionally, with use of the method in photovoltaic plants: electrical conductivity of the module glass surface, supplied voltage of the photovoltaic modules, electrical output of the photovoltaic modules. - measuring an insulation resistance (8, 18) of the unearthed electrical network, - determining a responding value for the insulation resistance, - triggering a warning signal if the measured insulation resistance falls below the responding value (14, 28), - wherein the responding value is determined dynamically as a momentary responding value in a warning value establishment process downstream of the insulation resistance measurement, - the momentary responding value is determined in the warning value establishment process as a function of a base value (R B), of setting parameters (R min, R ADY, R LIM), of ambient data and of an insulation resistance value averaged over time, and - the base value (R B) is a specific, fixed value of the insulation resistance for the network to be monitored, and - the following are used as setting parameters: a minimum responding value (R min) as a lower response limit value, an auxiliary value in the form of a responding value dynamic (R ADY) for defining a dynamic range in which the momentary responding value may change dynamically, and an auxiliary value in the form of responding value limits (R LIM) for determining a difference of the momentary responding value from the insulation resistance value averaged over time, and wherein - the momentary responding value is determined starting from the base value (R B) by a correction according to the ambient data, wherein the momentary responding value adopts the minimum responding value (R min) at its minimum and the value in the form of a responding value dynamic (R ADY) at its maximum and, within this dynamic range, lies below the insulation resistance value averaged over time, at least by the difference of the responding value limits (R LIM), and - the following influencing variables are incorporated as ambient data, either individually or in any combination, into the warning value establishment process: time, light intensity, temperature, atmospheric moisture, dew, salt content of the air, speed of change of the insulation resistance, number of people present in the region of the electrical plant, and additionally, with use of the method in photovoltaic plants: electrical conductivity of the module glass surface, supplied voltage of the photovoltaic modules, electrical output of the photovoltaic modules.