46db57fd__IP_Equivalency_Chart___Siemon__NEMA_Definition
[NEMA Rating] 4 [IP Equivalent] IP66 [IP Definition] 6 = Totally protected against dust [4] 6 = Protected against strong jets of water from all directions - Limited to ingress permitted. [NEMA Definition] 
Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt, rain, sleet, snow, windblown dust, splashing water, and hose-directed water; and that will be undamaged by the external formation of ice on the enclosure
NEMA Rating and IP Equivalency Chart - Siemon
NEMA Definition