An input adaptable electrical test set provides for the automatic detection of the power source connected to the test set, as well as automatic configuration of the test set to accommodate the identified power source. Prior to identification of the power source, a circuit breaker isolates a main transformer associated with the test set from receiving power from the power source. The main transformer includes a primary winding and a secondary winding, the primary winding having first, second and third tap positions that allows the transformer to be configured in one of two states depending on the power source connected to the test set. An automatic input voltage detection circuit monitors the input voltage provided by the unidentified power source and identifies the power source based on the monitored voltage. Based on the identification of the power source, the automatic input voltage detection circuit selects the configuration of the main transformer and the circuit breaker is closed to allow power from the power source to be supplied to the main transformer.