In this paper, a new index is proposed to find further information on voltage stability of ac/dc systems and reactive power requirements. The index defines two types of systems from the point of view of voltage stability and reactive power variations, soft and non-soft systems. This approach can assist for considering the reactive compensation, control and operation strategies for ac/dc applications as a function of their strength. Well known networks, including the modified IEEE 14 bus system, are studied with the new index. The Short Circuit Ratio, SCR, is traditionally used for dynamic studies of ac/dc interactions. Since SCR tells about the strength of ac/dc nodes, this relation will be used to qualify static and modal analyses in this work.