The IP ratings are defined in the IEC standard 60529, which was developed by the International Electrotechnical Commission. Specifically, IEC 60529 defines an enclosure as, "a part providing protection of equipment against certain external influences and in any direction protection against direct contact.” IEC 60529 does not include corrosion resistance, construction requirements, and the effects of icing and coolants. These are addressed in the NEMA 250 product standard, developed by the National Electrical Manufacturers Association.  IP ratings are much more limited and should be regarded as a supplement to a NEMA type designation, not as an equivalent specification.