Well,I think this is interesting.I invite people to think over it. consider a charged spherical shell.Throughout its interior,E=0. Now,consider the centre.From Laplace's equation and Earnshaw's theorem,this point is not a point of potential minimum.So,a charge at this point cannot be in stable equilibrium.Say,you displace it slightly. What do you find.It just gets stagnant where you left it! If this is not a point of stable eqlbm,it is not also a point of unstable equilibrium. So,is it a point of neutral equilibrium? Apparently seems so.But,I wish to confirm.