A luminaire nameplate can carry two completely independent claims in one line: Ex db IIC T6 Gb IP66. The Ex part says it will not ignite the atmosphere. The IP66 part says the enclosure will keep water and dust out. Buyers regularly confuse the two, and the mistake is expensive in both directions.
This guide covers what the two digits of an IP rating actually mean, which tests each rating passes, why an IP rating is not explosion protection, and how to pick the right level for a washdown bay, an offshore deck or a dusty silo.
What an IP rating is
An IP (Ingress Protection) rating is a two-digit code defined by IEC 60529 (adopted in Europe as EN 60529). It exists to replace vague marketing words such as “waterproof” or “dustproof” with a number that corresponds to a specific, repeatable test.
The code is written IP followed by two digits. The first digit covers solid objects and contact; the second covers liquids. Where a digit is replaced by the letter X, that category was not tested – it does not mean zero protection. So IPX4 is a rating for splashing water with the solids digit untested, and IP6X is dust-tight with no water claim.
| First digit | Protects against | Typical equipment |
|---|---|---|
| 0 | No protection | Exposed terminals indoors |
| 1 | Objects over 50 mm (back of hand) | Large open enclosures |
| 2 | Objects over 12.5 mm (finger) | Indoor accessories |
| 3 | Objects over 2.5 mm (tools, thick cable) | Older control gear |
| 4 | Objects over 1 mm (fine wire) | Standard panel enclosures |
| 5 | Dust-protected – limited ingress, no harmful deposit | Factory control boxes |
| 6 | Dust-tight – no ingress under vacuum test | Ex and outdoor enclosures |
Each level includes the levels below it, which is why an IP6X enclosure also satisfies IP5X and IP4X. For hazardous-area equipment you will almost always be specifying 5 or 6 in the first digit, because settled dust on a hot surface is itself an ignition risk, and because dust ingress can bridge clearances that the protection concept depends on.
The second digit is where most of the confusion lives, because levels 1 to 6 are cumulative but 7 and 8 are not. The water levels are not a single ladder you climb.
| Second digit | Test condition | Where it fits |
|---|---|---|
| 0 | No protection | Dry indoor locations |
| 1 | Vertical dripping water, 10 minutes | Condensation only |
| 2 | Dripping water at 15° tilt, 4 positions | Covered outdoor positions |
| 3 | Spray up to 60° from vertical | Lighting under eaves |
| 4 | Splashing water from any direction, 10 minutes | Outdoor sockets, canopies |
| 5 | Water jets, 6.3 mm nozzle, 12.5 L/min | Outdoor junction boxes |
| 6 | Powerful jets, 12.5 mm nozzle, 100 L/min | Washdown areas, marine decks |
| 7 | Immersion at 1 m for 30 minutes | Flood-prone pits, buried boxes |
| 8 | Continuous immersion, depth and duration set by the manufacturer | Submersible equipment |
| 9K | High-pressure, high-temperature jets (80 °C, up to 100 bar) | Food and beverage cleaning |
IP65 vs IP66 vs IP67 vs IP68: the four ratings buyers actually compare
Four ratings account for almost every specification argument. The difference between them is the failure mode each one was designed to survive.
| Rating | Water test | Failure mode it addresses | Typical Ex application |
|---|---|---|---|
| IP65 | 6.3 mm jet, 12.5 L/min, low pressure | Rain and light hosing | General outdoor luminaires and boxes |
| IP66 | 12.5 mm jet, 100 L/min, high pressure | Industrial hose-down, stormwater impact | Washdown bays, offshore decks |
| IP67 | Immersion at 1 m for 30 minutes | Static water pressure from pooling or flooding | Pits, sumps, ground-level boxes |
| IP68 | Continuous immersion, manufacturer-defined | Permanent submersion | Submersible pumps, submerged luminaires |
An IP rating is not explosion protection
This is the single most costly misunderstanding in hazardous-area procurement. An IP66 enclosure is dust-tight and jet-resistant. That says nothing about whether it can contain an internal explosion, whether its surface temperature is limited, or whether it can be installed in a Zone 1 area at all.
A 316 stainless steel enclosure with a perfect IP66 seal and no Ex marking is not legal in a classified area, however good it looks. Working in the other direction, an Ex d flameproof enclosure with only IP54 sealing can be technically certified and still fail within a year on a washdown deck, because water enters through the gland and corrodes the flame path.
Neither rating substitutes for the other, and neither one is optional. The area classification decides the Ex marking; the environment decides the IP rating. Both must be right.
How IP and Ex appear together on a nameplate
IEC 60079-0 sets a minimum ingress protection for each protection concept – broadly IP54 for flameproof and increased-safety apparatus in gas atmospheres, and IP6X where combustible dust is present. Those are floors, not targets. Manufacturers certify well above them because real installations are wetter and dustier than the minimum assumes.
Reading Ex db IIC T6 Gb IP66 therefore tells you:
- Ex db – flameproof enclosure, equipment protection level b, suitable for Zone 1 and Zone 2
- IIC – certified for the most demanding gas group, including hydrogen and acetylene
- T6 – maximum surface temperature 85 °C, safe for gases with an ignition temperature above that
- IP66 – dust-tight and resistant to powerful water jets
There is one practical trap. If a datasheet is silent on IP, the applicable figure is the minimum in the certificate, not the maximum the housing could achieve. Always ask for the IP rating as declared on the Ex certificate, because that is the number your acceptance inspector will check against.
Our explosion-proof junction boxes and distribution boxes are supplied with the IP rating stated on the certificate for exactly this reason, and the conduit fittings and cable glands are matched to the same figure.
Choosing the right IP rating for the environment
Rating by environment is more reliable than rating by habit. The table below maps the conditions that actually destroy equipment to the rating that survives them.
| Environment | What attacks the equipment | Sensible minimum |
|---|---|---|
| Indoor, dry, Zone 2 control room | Dust only | IP54 |
| General outdoor industrial | Rain, wind-driven water, dust | IP65 |
| Coastal or offshore | Driving salt spray, high humidity | IP66 with 316 stainless or GRP |
| Food, beverage and pharmaceutical washdown | Daily high-flow hosing, caustic cleaners | IP66, IP69K where steam or hot jets are used |
| Buried ducts, pits and sumps | Standing water, flooding | IP67, plus IP66 where jets are also present |
| Grain, coal, cement and other dust processes | Conductive or combustible dust layers | IP6X (required for Ex t) |
| Vibration-heavy housings (compressors, crushers) | Loosened glands and covers | IP66 plus mechanical retention, not a higher number |
Where IP ratings go wrong in practice
Almost every field failure we are asked to investigate traces back to one of six causes.
- The gland was not rated to match the box. An IP66 enclosure fitted with an IP54 gland is an IP54 assembly. Glands, blanking plugs and adaptors must carry at least the same ingress rating as the enclosure and, in a classified area, the same Ex concept.
- Seals replaced with generic parts. A compression gasket from a hardware shop will not restore IP66, and on flameproof equipment an unapproved gasket can void the certification outright.
- Unused entries left open. Every spare cable entry must be closed with a certified blanking plug. An open entry is both a water path and, on Ex d equipment, an ignition path.
- IP67 specified where jets are the real risk. Covered above, and still one of the most common specification errors in washdown plants.
- The X digit read as zero. IPX4 is a legitimate splash rating; it does not mean the enclosure failed the solids test.
- Confusing IP with Ex on a purchase order. Writing “IP66 stainless box, Zone 1” without naming the Ex concept leaves the supplier free to quote an uncertified enclosure.
What to demand on a quotation
Three questions separate a real specification from a marketing number.
- What IP rating is stated on the Ex certificate for this exact model, and can I have the certificate number?
- Are the cable glands and blanking plugs supplied at the same IP rating and the same Ex concept?
- Does the rating remain valid after the enclosure is opened for maintenance, and which spare parts are approved to restore it?
If a supplier cannot answer the second question, the assembly in the field will not be the assembly that was tested. We cover how to check the certificate behind the marking in how to verify an explosion-proof certificate.
IP rating questions we get asked most
Is IP68 better than IP66?
Not universally. IP68 is better against continuous immersion, which is what it was tested for. It says nothing about high-flow water jets, so it is not automatically better in a washdown environment. Where both risks are present, specify a dual rating such as IP66/IP68.
Can I install an IP65 luminaire outdoors?
For normal rain and light hosing, yes. For coastal exposure, high-flow cleaning or locations where stormwater impacts at speed, step up to IP66 and check the housing material. IP65 is the minimum for exposed outdoor locations, not a universal answer.
Does an IP66 enclosure count as explosion proof?
No. IP66 is an ingress rating from IEC 60529. Explosion protection comes from an Ex certification under IEC 60079, ATEX or UL 844 and depends on the protection concept, gas group and temperature class. A box can be IP66 and completely uncertified.
What IP rating do I need for a Zone 1 outdoor installation?
The zone sets the Ex marking; the weather sets the IP rating. For a Zone 1 outdoor position, IP65 is the practical floor and IP66 is the safer default, with the cable entries rated to match.
What does the X in IPX4 mean?
It means the solids digit was not tested or not specified, so no claim is made about dust or contact protection. It does not mean zero. In a hazardous area, an untested solids digit is usually unacceptable because dust ingress is a genuine ignition risk.
Send us the environment and we will match the IP rating to it. Tell us whether the position is indoor, outdoor, coastal or washed down, and the zone it sits in – we will come back with the enclosure, the glands and the certificate that covers the whole assembly.
