Analog circuit faults that produce indistinguishable test measurements are equivalent. Such faults cannot be diagnosed, since they defy fault location and/or value determination. In current simulation-before-test methods equivalent faults are found by inspecting fault simulation data. This approach is unsatisfactory for usually it imparts little information on which aspects of a circuit's design lead to equivalent faults or how diagnosis is to be improved. Presented is an examination of a subset of d.c. domain equivalent faults in steady-state linear analog circuits. The proposed methods for equivalent fault identification are aimed at increasing a test engineer's understanding of the faulty circuit's behaviour beyond that given by data analysis. Ways in which test design benefits from equivalent fault information are also discussed.