NEMA vs IP Ratings: How to Convert (And When You Can't)

NEMA (National Electrical Manufacturers Association) ratings and IP ratings from IEC 60529 both describe how well an enclosure protects its contents, but they are not interchangeable measurement systems. NEMA ratings are performance-based descriptions that bundle together dust, water, corrosion, ice, and even the ability to knock out two feet of ice for types 3R and 4X; IP ratings are single-digit test results for two axes only: solid objects and water.

The practical overlap: NEMA 4 and 4X enclosures (indoor/outdoor, hose-down rated) correspond to at least IP66, and most manufacturers test NEMA 4X enclosures as IP66. NEMA 6 and 6P are submersible ratings — 6P withstands prolonged submersion, which is the domain of IP67/IP68. NEMA 3R (outdoor rainproof) overlaps with IP32/IP34 territory, and NEMA 3/3S/3X adds windblown dust, generally aligning with IP55.

Here is where conversion breaks down. NEMA types 4X, 6, and 6P also certify corrosion resistance (for 4X), which IP ratings never test. A NEMA 4X stainless enclosure may carry IP66, but an IP66 enclosure has zero corrosion certification — the materials are up to the manufacturer. Similarly, NEMA 3R's sleet and ice tolerance has no IP equivalent.

The correct direction is one-way: you can safely claim an IP rating that is covered by the NEMA test (for example, a NEMA 4X enclosure is at least IP66), but you can never assume a NEMA type from an IP rating alone. Always check the manufacturer's datasheet for the specific NEMA type number that was certified.

For most procurement decisions, this rule of thumb works: if you need a NEMA 4X on the drawing, insist on the NEMA number. If you need IP66, IP67, or IP68 for a specific test standard, ask for the IP certificate and the lab report. On this site, the NEMA vs IP section includes a full conversion chart for all 16 common pairings.