A relay fault detection system structured to detect relay faults within a switching system, the switching system comprising: a first relay having an input structured to couple to a first signal, and having first and second outputs, the first output coupled to a termination resistor and the second output coupled to an output of the switching system, the first relay structured to couple the first signal to the first output or the second output of the first relay; a second relay having an input structured to couple to a second signal, and having first and second outputs, the second output coupled to a termination resistor and the first output coupled to the output of the switching system, the second relay structured to couple the second signal to the first output or the second output of the second relay; and a control system (270, 370) structured to operate the first and second relays to make exactly one of the first or second signals an active signal on the output of the switching system; characterized in that the relay fault detection system comprises: a first level detector coupled to the first signal and a second level detector coupled to the second signal, each of the first and second level detectors structured to generate a signal level output from the respective first signal and second signal; a first low threshold detector coupled to the first level detector and structured to detect a low signal level output of the first level detector as a signal fault when the first signal degrades below a low threshold; a second low threshold detector coupled to the second level detector and structured to detect a low signal level output of the second level detector as a signal fault when the second signal degrades below the low threshold; a first high threshold detector coupled to the first level detector and structured to detect a high signal level output of the first level detector in the presence of a first relay fault when the first signal is higher than a high threshold value; and a second high threshold detector coupled to the second level detector and structured to detect a high signal level output of the second level detector in the presence of a second relay fault when the second signal is higher than the high threshold value. a first relay having an input structured to couple to a first signal, and having first and second outputs, the first output coupled to a termination resistor and the second output coupled to an output of the switching system, the first relay structured to couple the first signal to the first output or the second output of the first relay; a second relay having an input structured to couple to a second signal, and having first and second outputs, the second output coupled to a termination resistor and the first output coupled to the output of the switching system, the second relay structured to couple the second signal to the first output or the second output of the second relay; and a control system (270, 370) structured to operate the first and second relays to make exactly one of the first or second signals an active signal on the output of the switching system; characterized in that the relay fault detection system comprises: a first level detector coupled to the first signal and a second level detector coupled to the second signal, each of the first and second level detectors structured to generate a signal level output from the respective first signal and second signal; a first low threshold detector coupled to the first level detector and structured to detect a low signal level output of the first level detector as a signal fault when the first signal degrades below a low threshold; a second low threshold detector coupled to the second level detector and structured to detect a low signal level output of the second level detector as a signal fault when the second signal degrades below the low threshold; a first high threshold detector coupled to the first level detector and structured to detect a high signal level output of the first level detector in the presence of a first relay fault when the first signal is higher than a high threshold value; and a second high threshold detector coupled to the second level detector and structured to detect a high signal level output of the second level detector in the presence of a second relay fault when the second signal is higher than the high threshold value. a first level detector coupled to the first signal and a second level detector coupled to the second signal, each of the first and second level detectors structured to generate a signal level output from the respective first signal and second signal; a first low threshold detector coupled to the first level detector and structured to detect a low signal level output of the first level detector as a signal fault when the first signal degrades below a low threshold; a second low threshold detector coupled to the second level detector and structured to detect a low signal level output of the second level detector as a signal fault when the second signal degrades below the low threshold; a first high threshold detector coupled to the first level detector and structured to detect a high signal level output of the first level detector in the presence of a first relay fault when the first signal is higher than a high threshold value; and a second high threshold detector coupled to the second level detector and structured to detect a high signal level output of the second level detector in the presence of a second relay fault when the second signal is higher than the high threshold value.