An electrical supply system including a voltage converter including having an input electrically coupled to a supply for receiving a supply signal and an output for supplying an output signal having a output voltage different to a supply voltage of the supply signal. The system includes a diode including a diode input electrically coupled to the voltage converter output, a bus electrically coupled to a diode output and at least one of a load and a store, a voltage sensor for detecting the output voltage, a current sensor for detecting a diode input current and an electronic processing device coupled to the sensors for monitoring the diode input current and the output voltage and detecting a fault in the electrical supply system based on at least the diode input current and output voltage.