A DC electrical current busbar associated with electrical load circuits and devices as well as sources requires protection. In order to provide such protection Kirchoff's laws are utilised such that electrical current values are substantially simultaneously taken and summed in order to identify deviations from expected differential threshold values. Upon detection of such deviations and generally as a result of a number of successive deviations an electrical isolation device is utilised in order to isolate electrical current to the busbar. The data set of electrical current values can be utilised in order to provide a back up protection system for individual electrical load devices and circuits, by similar comparison with expected values for those devices and circuits.