A device for estimating the insulation impedance of an alternating TT or TN electrical network comprising a neutral conductor connected to ground, at least one phase conductor and a ground conductor connected to the ground of the network, the network further comprising a load connected at least to the phase conductor and to the neutral conductor, the insulation impedance being the impedance between the load and the ground conductor, the device being intended to be connected to the neutral conductor, to the phase conductor and to the ground conductor upstream of the load, the device comprising: - an electrical circuit having an impedance of predetermined value and being connected between the phase conductor and the ground conductor, - a first switch configured to switch between an open state in which the first switch blocks the passage of a current between the phase conductor and the ground conductor through the electrical circuit and a closed state in which the first switch allows the passage of a current between the phase conductor and the ground conductor through the electrical circuit, - a first sensor configured to measure a first value of a voltage between the phase conductor and the ground conductor when the first switch is in the open state and to measure a second value of the voltage between the phase conductor and the ground conductor when the first switch is in the closed state, - a second sensor configured to measure a third value of a voltage between the neutral conductor and the ground conductor when the first switch is in the open state and to measure a fourth value of the voltage between the neutral conductor and the ground conductor when the first switch is in the closed state, and - a processing module configured to estimate the impedance of the insulation from the predetermined value of the impedance and the first, second, third and fourth measured values, the processing module being characterized in that it is configured to estimate a frequency of the current flowing in the phase conductor, to control the measurement, by the first and second sensors (60, 65), of first voltage samples with a multiple frequency of the calculated frequency and to estimate the first, second, third and fourth values from the first measured samples. - an electrical circuit having an impedance of predetermined value and being connected between the phase conductor and the ground conductor, - a first switch configured to switch between an open state in which the first switch blocks the passage of a current between the phase conductor and the ground conductor through the electrical circuit and a closed state in which the first switch allows the passage of a current between the phase conductor and the ground conductor through the electrical circuit, - a first sensor configured to measure a first value of a voltage between the phase conductor and the ground conductor when the first switch is in the open state and to measure a second value of the voltage between the phase conductor and the ground conductor when the first switch is in the closed state, - a second sensor configured to measure a third value of a voltage between the neutral conductor and the ground conductor when the first switch is in the open state and to measure a fourth value of the voltage between the neutral conductor and the ground conductor when the first switch is in the closed state, and - a processing module configured to estimate the impedance of the insulation from the predetermined value of the impedance and the first, second, third and fourth measured values, the processing module being characterized in that it is configured to estimate a frequency of the current flowing in the phase conductor, to control the measurement, by the first and second sensors (60, 65), of first voltage samples with a multiple frequency of the calculated frequency and to estimate the first, second, third and fourth values from the first measured samples.