A traction voltage system in a vehicle includes a junction box with multiple connectors for electrical components, which components include electrical supplies and electrical loads, and an electronic control unit arranged to monitor current flowing flow to or from the components. A controller or a circuit breaker is arranged to control the supply of power to each respective component, and at least all but one of the connectors are provided with a current sensor arranged to transmit a signal representing detected current values to the electronic control unit. The electronic control unit is arranged to determine an instantaneous current value flowing to or from each component, to compare the instantaneous current value with a predetermined limit value for each connector, and to take action in response to the comparison. A method for controlling the traction voltage system is also provided.