Self-calibration system for autonomous loop impedance measuring devices, said measuring devices having a loop impedance sensor for a grounding conductor, wherein the self-calibration system comprises a processing device connected to the impedance sensor, wherein said processing device is formed by a containment housing inside which it comprises - a microprocessor having a storage memory; - an auxiliary loop including at least two precision resistors arranged in parallel and selectively activated by means of a switch respectively for each of them, said auxiliary loop being arranged in parallel with a loop resistance (Rb) to be measured, wherein each precision resistor has a certain value, these values being different from each other; and - power supply means; wherein the self-calibration system further comprises means of communication with a data receiving device; wherein a normalized calibration curve (8.1) of the measuring device has at least two different ranges of values, and there is at least one resistance value comprised in each range of the calibration curve; wherein the self-calibration system has a ground impedance calculation algorithm that allows the application of this system for adjusting a current injection frequency and impedance calculation to unattended monitoring of loops that are closed by the physical ground; and wherein the self-calibration system is configured to implement an initial stage for obtaining the normalized calibration curve (8.1) of the measuring device and introduction of the normalized values (8.2) of said calibration curve in the memory of a processing device, and a self-calibration stage which has the phases of - obtaining the range in which the measured loop resistance (Rb) is included by connecting the at least one precision resistor of each range of the normalized calibration curve (8.1) from a sequential activation (13 (n)) of the switches corresponding to each precision resistor, so that the activation of each switch configures an equivalent circuit between the loop of the measuring device and the auxiliary loop corresponding to the precision resistor associated with said switch, and; - calculating the loop impedance values based on the obtained range. - a microprocessor having a storage memory; - an auxiliary loop including at least two precision resistors arranged in parallel and selectively activated by means of a switch respectively for each of them, said auxiliary loop being arranged in parallel with a loop resistance (Rb) to be measured, wherein each precision resistor has a certain value, these values being different from each other; and - power supply means; wherein the self-calibration system further comprises means of communication with a data receiving device; wherein a normalized calibration curve (8.1) of the measuring device has at least two different ranges of values, and there is at least one resistance value comprised in each range of the calibration curve; wherein the self-calibration system has a ground impedance calculation algorithm that allows the application of this system for adjusting a current injection frequency and impedance calculation to unattended monitoring of loops that are closed by the physical ground; and wherein the self-calibration system is configured to implement an initial stage for obtaining the normalized calibration curve (8.1) of the measuring device and introduction of the normalized values (8.2) of said calibration curve in the memory of a processing device, and a self-calibration stage which has the phases of wherein the self-calibration system further comprises means of communication with a data receiving device; wherein a normalized calibration curve (8.1) of the measuring device has at least two different ranges of values, and there is at least one resistance value comprised in each range of the calibration curve; wherein the self-calibration system has a ground impedance calculation algorithm that allows the application of this system for adjusting a current injection frequency and impedance calculation to unattended monitoring of loops that are closed by the physical ground; and wherein the self-calibration system is configured to implement an initial stage for obtaining the normalized calibration curve (8.1) of the measuring device and introduction of the normalized values (8.2) of said calibration curve in the memory of a processing device, and a self-calibration stage which has the phases of - obtaining the range in which the measured loop resistance (Rb) is included by connecting the at least one precision resistor of each range of the normalized calibration curve (8.1) from a sequential activation (13 (n)) of the switches corresponding to each precision resistor, so that the activation of each switch configures an equivalent circuit between the loop of the measuring device and the auxiliary loop corresponding to the precision resistor associated with said switch, and; - calculating the loop impedance values based on the obtained range.