The aim of the study is to develop a method for parametric matching of insulation monitoringdevices, unearthed DC distribution systems and discrete inputs of relay protection.The use of unearthed DC distribution systems for power supply to relay protection devicesand other responsible consumers makes it possible to ensure high reliability and safety during their operation. It is necessary to ensure uninterrupted power supply to these consumerseven in the event of a ground fault in one of the DC distribution network poles. Insulationmonitoring of the network poles and the prompt execution of repair work when the insulationresistance falls below the critical level set by the response value, are a guarantee of highreliability of power supply. The article discusses the reasons leading to dangerous levels ofpole voltage unbalance and false triggering of relay protection discrete inputs during groundfaults of the signal lines connected to them. A method based on multivariate DC analysis isproposed to determine the matched insulation monitoring response value with the DC networkparameters and discrete inputs parameters, when the conditions for the occurrence ofsuch accidents are excluded. The influence of insulation monitoring devices in a DC systemon pole voltages unbalance and relay protection operation is also considered. A modificationof the insulation monitoring active method is proposed, which does not create additional polevoltage unbalance and risks of relay protection misoperation. The operating range of thestatic characteristics of the pole voltages and leakage current measuring transducers is narrowedin the grid unbalanced modes by using a modified active insulation monitoring met hod.Estimates of the increase in the insulation resistance measurement error arising in thesemodes are obtained.