A protection device for protecting an electrical system in a vehicle, the electrical system including a battery pack having at least one contactor (S1, S2, S3), and a high voltage bus connected to the battery pack , the protection device comprising: a microcontroller which generates test pulses at a pulse output terminal thereof and includes a sense input terminal, the microcontroller having additional output terminals coupled to a control terminal of the at least one contactor (S1, S2, S3); a first capacitor having a first terminal coupled to a first terminal of the at least one contactor (S1, S2, S3); a second capacitor having a first terminal coupled to a second terminal of the at least one contactor (S1, S2, S3); and circuitry coupled between the microcontroller and the first and second capacitors, the circuitry having an input terminal connected to the pulse output terminal of the microcontroller and an output terminal connected to the sense input terminal of the microcontroller , the circuitry is configured, if each contactor (S1, S2, S3) is open, to reflect the test pulses to the sense input terminal of the microcontroller when the microcontroller applies a contactor opening voltage to the control terminal of the at least one contactor (S1, S2, S3) to open the same, the circuitry is configured, when the microcontroller applies a contactor closing voltage to the control terminal of any of the at least one contactor (S1, S2, S3) closing the same, to provide a signal at a voltage level of a battery voltage of a battery (V3) of the circuitry to the sense input terminal of the microcontroller , the circuitry is further configured to present a signal different from the reflected test pulses at a voltage level between ground and the battery voltage of the battery (V3) of the circuitry to the sense input terminal of the microcontroller if any contactor (S1, S2, S3) is welded shut when the microcontroller applies the contactor opening voltage to the control terminal of the at least one contactor (S1, S2, S3). a microcontroller which generates test pulses at a pulse output terminal thereof and includes a sense input terminal, the microcontroller having additional output terminals coupled to a control terminal of the at least one contactor (S1, S2, S3); a first capacitor having a first terminal coupled to a first terminal of the at least one contactor (S1, S2, S3); a second capacitor having a first terminal coupled to a second terminal of the at least one contactor (S1, S2, S3); and circuitry coupled between the microcontroller and the first and second capacitors, the circuitry having an input terminal connected to the pulse output terminal of the microcontroller and an output terminal connected to the sense input terminal of the microcontroller , the circuitry is configured, if each contactor (S1, S2, S3) is open, to reflect the test pulses to the sense input terminal of the microcontroller when the microcontroller applies a contactor opening voltage to the control terminal of the at least one contactor (S1, S2, S3) to open the same, the circuitry is configured, when the microcontroller applies a contactor closing voltage to the control terminal of any of the at least one contactor (S1, S2, S3) closing the same, to provide a signal at a voltage level of a battery voltage of a battery (V3) of the circuitry to the sense input terminal of the microcontroller , the circuitry is further configured to present a signal different from the reflected test pulses at a voltage level between ground and the battery voltage of the battery (V3) of the circuitry to the sense input terminal of the microcontroller if any contactor (S1, S2, S3) is welded shut when the microcontroller applies the contactor opening voltage to the control terminal of the at least one contactor (S1, S2, S3). <EOS>