  We study multiple helical nanowires in proximity to a common mesoscopic
superconducting island, where Majorana fermion bound states are formed. We show
that a weak finite charging energy of the center island may dramatically affect
the low-energy behavior of the system. While for strong charging interactions,
the junction decouples the connecting wires, interactions lower than a
non-universal threshold may trigger the flow towards an exotic Kondo fixed
point. In either case, the ideally Andreev reflecting fixed point
characteristic for infinite capacitance (grounded) devices gets destabilized by
interactions.
