An electrical distribution circuit comprising: an input connectable to an AC source (12a-12c); a three-phase output connectable to terminals of an electrical machine, the three-phase output configured to provide three-phase voltages and currents to the electrical machine; one or more circuit components positioned between the input and the output configured to control three-phase voltages and currents to the output; and a diagnostic system configured to detect an excess voltage drop EVD fault in the electrical distribution circuit, the diagnostic system comprising a processor that is programmed to: receive three-phase voltages and currents provided to the terminals of the electrical machine; determine fundamental components of the three-phase voltages and currents provided to the terminals; compute a positive sequence current, negative sequence current, and zero sequence current from the fundamental components of the three-phase currents; extract a compensated negative sequence current from the negative sequence current component, the compensated negative sequence current being a component of the negative sequence current that is due solely to an EVD characterized in that additionally the processor is programmed to: add the compensated negative sequence current to the positive sequence current to determine fault reference current phasors; determine a negative sequence current reference phase angle for each phase based in part on a phase angle of the positive sequence current; and identify an EVD fault in the electrical distribution circuit based on the compensated negative sequence current, the fault reference current phasors, and the negative sequence current reference phase angles. an input connectable to an AC source (12a-12c); a three-phase output connectable to terminals of an electrical machine, the three-phase output configured to provide three-phase voltages and currents to the electrical machine; one or more circuit components positioned between the input and the output configured to control three-phase voltages and currents to the output; and a diagnostic system configured to detect an excess voltage drop EVD fault in the electrical distribution circuit, the diagnostic system comprising a processor that is programmed to: receive three-phase voltages and currents provided to the terminals of the electrical machine; determine fundamental components of the three-phase voltages and currents provided to the terminals; compute a positive sequence current, negative sequence current, and zero sequence current from the fundamental components of the three-phase currents; extract a compensated negative sequence current from the negative sequence current component, the compensated negative sequence current being a component of the negative sequence current that is due solely to an EVD characterized in that additionally the processor is programmed to: add the compensated negative sequence current to the positive sequence current to determine fault reference current phasors; determine a negative sequence current reference phase angle for each phase based in part on a phase angle of the positive sequence current; and identify an EVD fault in the electrical distribution circuit based on the compensated negative sequence current, the fault reference current phasors, and the negative sequence current reference phase angles. receive three-phase voltages and currents provided to the terminals of the electrical machine; determine fundamental components of the three-phase voltages and currents provided to the terminals; compute a positive sequence current, negative sequence current, and zero sequence current from the fundamental components of the three-phase currents; extract a compensated negative sequence current from the negative sequence current component, the compensated negative sequence current being a component of the negative sequence current that is due solely to an EVD characterized in that additionally the processor is programmed to: add the compensated negative sequence current to the positive sequence current to determine fault reference current phasors; determine a negative sequence current reference phase angle for each phase based in part on a phase angle of the positive sequence current; and identify an EVD fault in the electrical distribution circuit based on the compensated negative sequence current, the fault reference current phasors, and the negative sequence current reference phase angles.