IEC 61753-031-3:2009 contains the minimum initial tests and measurement requirements and severities which a non-wavelength selective branching device (NWBD) should satisfy in order to be categorized as meeting the requirements of Category U (uncontrolled environment) as defined in Annex A of IEC 61753-1. Keywords: non-wavelength selective branching device (NWBD), Category U (uncontrolled environment)