Smart Junction Box (CJF-400) is intended to protect the main branch of a fieldbus installation in hard IEC61158-2 (PROFIBUS PA fieldbus and FoundationTM) against short circuits generated in leads or branches (between + and -) , limiting the current around 50 mA, the way this spurious does not propagate in the other branches, and not in the main branch. The lead that was short, should operate again as soon as the short is removed.