Abstract: The disclosure provides a vehicle electrical system equipped with a high-voltage branch and a first low-voltage branch, which is galvanically isolated from the high-voltage branch by insulation. The low-voltage branch has at least one low-voltage line, which leads to the high-voltage branch. The low-voltage branch has a voltmeter. The voltmeter is connected in a signal-transmitting manner to the at least one low-voltage line. Furthermore, the voltmeter is set up to detect whether an absolute voltage value of the at least one low-voltage line with respect to a ground potential of the vehicle electrical system lies above a voltage limit. The voltage limit defines an absolute voltage value which is greater than the absolute value of a maximum signal voltage of the low-voltage line, which the low-voltage line has during fault-free operation.