IP is an acronym for “Ingress Protection” against objects that intrude into the enclosure of any type of equipment.
The IP ratings are defined in the IEC standard 60529, which was developed by the lnternational 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."¹
The scope of IEC 60529 does not include corrosion resistance, construction requirements, and the effects of icing and coolants. These and additional aspects are addressed in the NEMA 250 product standard, developed by the National Electrical Manufacturers Association.
With its more limited scope, an IP rating can be regarded as a supplement to a NEMA rating, but not as its equivalent. Consequently, caution is advised when using any IP/NEMA rating cross-reference tables published on the Internet.
For more details refer to the NEMA publication, A Brief Comparison of NEMA 250—Enclosures for Electrical Equipment (1000 Volts Maximum) and IEC 60529—Degrees of Protection Provided by Enclosures (IP Code) .²
The IP rating is formatted as “IP” followed by two digits. The first digit indicates a protection level against solids such as dust, and the second digit indicates a protection level against liquids. Figure 1 illustrates the IP formats and uses IP56 as an example.