A power conversion unit, PCU, having at least one input terminal and at least one output terminal, the PCU comprising: a power converter circuit; a safety detection circuit including a plurality of known network impedances and a switch having a first end coupled between two of the plurality of network impedances (302, 304, 306, 308) and a second end coupled to a first output terminal of the at least one output terminal; and a controller communicatively coupled to the safety detection circuit and the at least one power converter circuit, the controller being configured to: measure one or more voltage values associated with the PCU; operate the switch at least in part by changing a state of the switch from a first state to a second state; measure a first voltage between Protective Earth, PE, and the first output terminal while the switch is in the second state; operate the switch at least in part by changing the state of the switch from the second state to the first state; measure a second voltage value of PE relative to the first output terminal while the switch is in the first state; and calculate an insulation impedance between PE and one or more of the at least one input terminal and the at least one output terminal based on the first voltage, the second voltage, the one or more voltage values associated with the PCU, and the plurality of known network impedances (302, 304, 306, 308). a power converter circuit; a safety detection circuit including a plurality of known network impedances and a switch having a first end coupled between two of the plurality of network impedances (302, 304, 306, 308) and a second end coupled to a first output terminal of the at least one output terminal; and a controller communicatively coupled to the safety detection circuit and the at least one power converter circuit, the controller being configured to: measure one or more voltage values associated with the PCU; operate the switch at least in part by changing a state of the switch from a first state to a second state; measure a first voltage between Protective Earth, PE, and the first output terminal while the switch is in the second state; operate the switch at least in part by changing the state of the switch from the second state to the first state; measure a second voltage value of PE relative to the first output terminal while the switch is in the first state; and calculate an insulation impedance between PE and one or more of the at least one input terminal and the at least one output terminal based on the first voltage, the second voltage, the one or more voltage values associated with the PCU, and the plurality of known network impedances (302, 304, 306, 308). measure one or more voltage values associated with the PCU; operate the switch at least in part by changing a state of the switch from a first state to a second state; measure a first voltage between Protective Earth, PE, and the first output terminal while the switch is in the second state; operate the switch at least in part by changing the state of the switch from the second state to the first state; measure a second voltage value of PE relative to the first output terminal while the switch is in the first state; and calculate an insulation impedance between PE and one or more of the at least one input terminal and the at least one output terminal based on the first voltage, the second voltage, the one or more voltage values associated with the PCU, and the plurality of known network impedances (302, 304, 306, 308).