Circuit apparatus (SV) for detecting a state of an electrical interlock loop (VS) for monitoring at least one high-voltage component (HK), comprising: - a power connection (SA1) for electrical connection to a voltage source; - a ground connection (ML) for electrical connection to an electrical ground (MS); - a positive connection (PA) for electrical connection to a line end (LE1) of the interlock loop (VS); - a negative connection (NA) for electrical connection to a further line end (LE2) of the interlock loop (VS), characterized in that the circuit apparatus (SV) furthermore comprises: - a controllable current source (SQ) for providing the two currents (I1, 12), said current source being electrically connected between the negative connection (NA) and the ground connection (ML); - a measuring arrangement (MA) for measuring the voltage potential ( Φ ) at the negative connection (NA) when two mutually different currents (I1, 12) flow from the power connection (SA1) via the negative connection (NA) to the ground connection (ML); and - a detector arrangement (EA), which comprises a comparison unit (KP) for comparing the two potential measurement values ( Φ 1, Φ 2) of the voltage potential ( Φ ) that are measured at the two currents (I1, 12) with in each case two predefined potential reference values (Ur1, Ur2 and Ur3, Ur4, respectively) and which is configured to ascertain, based on the comparison results of the comparison unit (KP), whether the negative connection (NA) is electrically short-circuited with the positive connection (PA), the power connection (SA1) or the ground connection (ML), or with none of these connections (PA, SA1, ML); wherein a fault-free state of the interlock loop (VS) is ascertained if the first potential measurement value ( Φ 1) lies between the first (Ur1) and the second (Ur2) potential reference value and the second potential measurement value ( Φ 2) is greater than the fourth potential reference value (Ur4) . - a power connection (SA1) for electrical connection to a voltage source; - a ground connection (ML) for electrical connection to an electrical ground (MS); - a positive connection (PA) for electrical connection to a line end (LE1) of the interlock loop (VS); - a negative connection (NA) for electrical connection to a further line end (LE2) of the interlock loop (VS), - a controllable current source (SQ) for providing the two currents (I1, 12), said current source being electrically connected between the negative connection (NA) and the ground connection (ML); - a measuring arrangement (MA) for measuring the voltage potential ( Φ ) at the negative connection (NA) when two mutually different currents (I1, 12) flow from the power connection (SA1) via the negative connection (NA) to the ground connection (ML); and - a detector arrangement (EA), which comprises a comparison unit (KP) for comparing the two potential measurement values ( Φ 1, Φ 2) of the voltage potential ( Φ ) that are measured at the two currents (I1, 12) with in each case two predefined potential reference values (Ur1, Ur2 and Ur3, Ur4, respectively) and which is configured to ascertain, based on the comparison results of the comparison unit (KP), whether the negative connection (NA) is electrically short-circuited with the positive connection (PA), the power connection (SA1) or the ground connection (ML), or with none of these connections (PA, SA1, ML); <EOS>