Foreseeing practical applications of recently discovered new series of superconductor —Fe-pnictides, one of the most important parameters is current transport across grain boundaries. We combined SQUID measurements, magneto-optical (MO) imaging, scanning and transmission electron microscope (SEM and TEM) and low temperature laser scanning microscope (LTLSM) in order to understand the relationship between the microstructure and intergrain current transport, so called global current, in a random polycrystalline SmFeAsO_0.85 (Sm1111) bulk. Our Sm1111 bulk showed significant global critical current density (J_c) which is more than one magnitude higher compared to random polycrystalline pure YBCO bulks at self field and the same temperature. However there was different temperature dependence of intergrain and intragrain J_c, exhibiting granularity at low temperature which was caused by large difference of J_c on two distinct scales. Strikingly most of intergrain current transport at self field relied on SNS Josephson weak links where supercurrent passed across the conductive impurity phase of FeAs, strongly suggesting the need of eliminating such a wetting phase in order to explore internal blocking effects at grain boundaries which are not fully understood yet.