  Following our recent work [New J. Phys. 10, 053011, (2008)], here we
demonstrate that due to strong nonlocal effects additional boundary conditions
are essential to characterize the reflection of electromagnetic waves by
nonconnected wire arrays using homogenization methods. Based on simple physical
considerations, we derive the additional boundary conditions for the case where
the wire medium is adjacent either to a dielectric or to a conducting material,
and demonstrate that in the lossless case such boundary conditions ensure the
conservation of the power flow. It is shown that the number of additional
boundary conditions is related to the number of metallic wires in a unit cell.
We illustrate the application of the novel boundary conditions to several
configurations with practical interest.
