This information is from the NEMA Standards Publication No. 250 “Enclosures for Electrical Equipment (1000 Volts Maximum)”
Type 4X Enclosures Description and Application
Type 4X enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against corrosion, windblown dust and rain, splashing water, hose-directed water, and damage from external ice formation. They are not intended to provide protection against conditions such as internal condensation or internal icing.