Short answer: you can line the two scales up in a table, but the lines are not equal signs. An IP code from IEC 60529 states what two laboratory tests proved about solids and water. A NEMA type from NEMA 250 describes performance against a wider list of conditions, including corrosion and ice. A rough conversion works for comparing products across markets; it does not work for swapping a rating on a drawing, because no IP test proves a NEMA type and no NEMA type proves an IP code.
What each scale actually states
An IP code is two digits after the letters IP. The first digit covers solids, from no protection (0) through fingers and tools up to dust-tight (6). The second digit covers water, from dripping water (1) through rain (3), splashing (4), hose jets (5 and 6), temporary immersion (7) and continuous immersion (8). A digit X means that protection was not tested. The digit-by-digit definitions are laid out in the IP rating chart, so we will not repeat them here.
A NEMA type is a single number that bundles several conditions together. Type 1 covers incidental contact indoors. Type 3R covers rain, sleet and snow outdoors. Type 4 adds hose-directed water, which is why it is the washdown type. Type 4X is Type 4 plus corrosion resistance. Type 6 and 6P cover submersion. Type 12 and 13 are indoor types for dust, dripping liquids and oil or coolant spray. Types 7 through 10 are hazardous-location types, which we do not build. The full type-by-type breakdown is in the NEMA enclosure types guide.
The key difference is the shape of the claim. IP gives you a fine-grained pair of test results. NEMA gives you one coarse verdict across many conditions at once.
The conversion table, with its limits
NEMA publishes a comparison between its own types and IEC 60529 codes. Read it in one direction only: an enclosure that meets the NEMA type is expected to also meet the listed IP code. The reverse does not follow, because the NEMA tests cover conditions the IP tests never run.
| NEMA type | Roughly equivalent IP | What the NEMA type adds that IP does not test |
|---|---|---|
| 1 | IP20 | Constructed for indoor general purpose use |
| 3R | IP14-level rain protection | Rain, sleet, snow; undamaged by ice |
| 4 | IP66 | Hose-directed water from any direction |
| 4X | IP66 | Type 4 plus corrosion resistance |
| 6 | IP67 | Entry of water during brief submersion, limited depth |
| 6P | IP68-level submersion | Prolonged submersion, corrosion resistance |
| 12 | IP54 | Indoor dust, dripping non-corrosive liquids |
| 13 | IP54 | Indoor oil and coolant spray |
Two cautions when you use this table. First, the equivalences are approximate. The test setups differ: hose pressure, jet distance, immersion depth and duration are not identical between the two standards. Second, the arrow points one way. An IP66 rating alone says nothing about corrosion, gasket aging or ice, so it cannot stand in for Type 4X on a washdown or outdoor specification. That one-direction rule is the whole point of an IP-to-NEMA conversion, and forgetting it is the most common spec mistake.
Why the codes are not interchangeable on a drawing
In United States installations the NEC is explicit that IP ratings are not a substitute for enclosure type ratings. An inspector checking a panel against Table 110.28 looks for a NEMA type number. If your drawing says IP66 and nothing else, you have given the inspector a code the NEC does not accept for that purpose, and the panel can be rejected on paper alone.
The safe practice is to carry both. Specify the NEMA type for the installation and the IP code for any IEC-market requirement, and check the edition your authority having jurisdiction enforces. Many enclosures are dual-marked for exactly this reason. Our stainless wall-mount and HMI enclosures are rated NEMA 4X-type / IP66 by the manufacturer; not UL listed. Note the wording: the rating belongs to the manufacturer, and NEMA itself does not test, certify or endorse enclosures. When a project requires a listed box, see the guide to UL 50E and NEMA 250 listing for what listing actually involves.
There is a second reason the two scales resist conversion: ratings describe the enclosure as tested, not the enclosure as installed. Cut a hole, fit a gland or mount a device, and the assembly is only as good as the weakest penetration. That is the weakest-link rule the NEMA 4 vs 4X vs IP66 comparison works through in detail.
Reading an IP code in thirty seconds
When a datasheet says IP67, decode it as a sentence: sealed against dust (6), safe under 1 m of water for 30 minutes (7). When it says IP4X, dust protection was not tested, only tools and wires. When it says IPX5, only the water jet was tested. That X is not decoration; it tells you the manufacturer skipped that test, and you cannot assume the protection exists.
For enclosure work, three second digits matter most:
- 6 (powerful jets): washdown, hose-directed cleaning, driving rain on a moving vehicle. This is the digit behind Type 4 and 4X equivalents.
- 7 (temporary immersion, 1 m, 30 minutes): flood-prone pits, buried hand holes, short submersion. Closest to Type 6.
- 8 (continuous immersion under stated conditions): a manufacturer-defined condition, so read the stated depth and duration, not just the digit. It lines up best with Type 6P.
If a device datasheet cites an IP rating and you are putting it inside one of our enclosures, the numbers do not add and they do not average. The assembly's rating is the lower of the two.
What the tests do not prove
Neither scale rates what panel builders actually worry about most. Neither test covers:
- Corrosion. Type 4X and 6P include it; IP codes never mention it. Salt air and sanitizer spray are material choices, not rating digits.
- Temperature and condensation. A sealed IP66 box can still fog internally on a cold night. The condensation guide explains why a passing rating does nothing about dew point inside the box.
- UV, gasket aging and door cycling. A five-year-old gasket may not reproduce the factory test.
- Impact and vibration. Separate standards entirely.
That gap matters when a specification says only "IP66 minimum" for an outdoor site. The IP code guarantees the water test in the lab. It says nothing about the salt fog, the sun or the freezing rain the same box will see, and those are what decide whether the box lasts.
Converting in the other direction: NEMA to IP
European customers and IEC-based specs ask the question backwards: our panel is Type 4X, what IP code do we declare? The same NEMA comparison table gives IP66 as the expected equivalent. Declare it as "equivalent," not as a test result, unless the enclosure has actually been tested to IEC 60529. If the customer's contract demands a tested IP code, the enclosure needs IEC 60529 testing in its own right.
A practical compromise, and one that avoids most cross-border arguments, is to specify enclosures that carry both markings from the manufacturer. Then each market reads the number it knows, and nobody converts anything.
What to specify
Put the NEMA type on US drawings; add the IP code when the spec or the export market wants it. Match the type to the worst condition at the site, not to the closest table row: hose washdown gets Type 4, corrosive washdown gets 4X in 304 or 316L stainless, submersion gets 6P, indoor oil mist gets 13. Browse the stainless range in the size finder, or send your own size and cutouts through the custom enclosure builder. And whatever the nameplate says, treat the rating as belonging to the sealed box as delivered: every penetration you add afterwards is yours to keep tight.
Questions
Is IP66 the same as NEMA 4X?
No. IP66 means the enclosure passed a dust test and a powerful water-jet test. NEMA Type 4X covers hose-directed water plus corrosion resistance, ice and other conditions the IP tests never check. A NEMA 4X enclosure will usually meet IP66, but an IP66 rating alone does not prove Type 4X. On a US specification, ask for the NEMA type.
Can I convert a NEMA type to an IP code for a European customer?
You can give an approximate equivalent: Type 4 and 4X correspond roughly to IP66, Type 3R to IP14-style rain protection, Type 6 to IP67, and Type 12 to IP54. But the conversion is a comparison of published tables, not a test result. If the customer's specification calls for an IP code, the enclosure needs to be tested or rated to IEC 60529, not merely converted.
Which one should I put on the drawing?
In the United States, put the NEMA type: the NEC treats IP ratings as not a substitute for enclosure type ratings. In IEC markets, put the IP code. Many enclosures carry both, which satisfies the specification and the inspector at once. Note any rating after field cutouts changes, regardless of the number on the nameplate.
Does IP67 beat IP66 because the number is higher?
Not in practice. The second digit 6 means powerful water jets; the digit 7 means temporary immersion in still water. The tests are different, not cumulative, so an IP67 enclosure has not proven it survives a hose blast. An enclosure that meets both is marked IP67 only if it also passed the jet test first, which is why you see dual codes like IP66/67.
