Device and method for improving safety in a vehicle

A power source (205) supplies power, via a first line (L210), to an apparatus (260) in the vehicle (100; 110) and, via a second line (L211), to an electronic device (240). The first line (L210) comprises a breaker device (250) for interrupting the power supply via said first line (L210) under certain circumstances. The electronic device (240), e.g. a tachograph, is intended to be supplied with power continuously. The second line (L211) comprises a safety device (230) adapted to interrupt the power supply at a predetermined amperage (Ib1) and the breaker device (250) is housed in an enclosure (270). The power supply in said second line (L211) is interrupted at a lower amperage (Ith) than said predetermined amperage (Ib1) by means of a further safety device (220), which further safety device (220) is arranged in said second line (L211) upstream of said safety device (230) in the enclosure (270).