IP Rating and NEMA Type: Mapping Two Different Systems

North American enclosures are rated by NEMA type, the rest of the world by IP code, and datasheets often print both. The two systems test different things and the correspondence is approximate.

What NEMA adds

NEMA 250 includes a hose-down test, but also corrosion resistance, gasket ageing and, for some types, a construction review. NEMA 4X specifically requires a corrosion resistant enclosure, which IP66 says nothing about. Conversely, IP testing covers the dust chamber in more detail than most NEMA types require.

Common mapping

NEMA 4 is often mapped to IP66 and NEMA 4X to IP66 plus corrosion resistance. NEMA 12 maps roughly to IP54. These are rough equivalences used for procurement, not test equivalences, and a product certified to one should not be assumed to meet the other.

Practical advice

If the installation is in North America and the specification calls for NEMA 4X, supply a NEMA listed product. If the specification is IEC based, supply an IP rated one. Where both markets matter, test to both rather than relying on a mapping table, and state the test laboratory in the datasheet.

Related technical notes

• Why Water Enters from Below: The Underside Problem
• Nozzle Calibration: The Number That Decides the Test
• The Spray Nozzle Alternative for IPX3 and IPX4