The method of determination of effective characteristics of a 3-D periodic structure with small spacing was presented. It was applied to a structure of parallel wires with nonconducting coating. An effective permittivity of this structure was obtained. It contains an effective plasma frequency and some parameter that is responsible for spatial dispersion. The dependencies of these parameters on electromagnetic and geometric characteristics of structure were analyzed. Particularly, it was shown that the role of spatial dispersion decreases with increase in the coating permittivity and the coating permeability. The magnetic coating is more effective for the taming of spatial dispersion but the dielectric coating is simpler for fabriacation.