The IP rating is both the most frequently cited and the most widely misunderstood specification in data sheets for mobile systems. It describes the result of a type test conducted under standardized conditions – not the operational durability of a device in the field. In procurement, three assumptions routinely lead to false expectations: that a higher second numeral always denotes greater protection, that the rating remains valid indefinitely, and that it implies explosion protection.
How the marking is structured
The IP code is defined in DIN EN 60529, the German version of the international standard IEC 60529. The two numerals represent two mutually independent tests.
The first characteristic numeral describes the degree of protection against ingress of solid foreign objects and against access to hazardous parts.
| Numeral | Protection against solid foreign objects |
|---|---|
| 0 | non-protected |
| 1 | solid foreign objects ≥ 50 mm diameter |
| 2 | solid foreign objects ≥ 12.5 mm |
| 3 | solid foreign objects ≥ 2.5 mm |
| 4 | solid foreign objects ≥ 1 mm |
| 5 | dust-protected – dust ingress is not entirely prevented, but does not penetrate in harmful quantities |
| 6 | dust-tight – no ingress of dust |
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In practice, the distinction between 5 and 6 is more significant than it appears. "Dust-protected" does not mean dust-free: dust may penetrate as long as it does not impair functionality. In an environment with conductive dust – such as metal processing or coal dust – this carries different implications than in a dry equipment room.
The second characteristic numeral describes the degree of protection against ingress of water.
| Numeral | Protection against ingress of water |
|---|---|
| 0 | non-protected |
| 1 | vertically falling water drops |
| 2 | vertically falling water drops when enclosure tilted up to 15° |
| 3 | spraying water at any angle up to 60° from the vertical |
| 4 | splashing water from any direction |
| 5 | water jets projected by a nozzle |
| 6 | powerful water jets projected by a larger nozzle |
| 7 | temporary immersion in water |
| 8 | continuous immersion under agreed conditions |
| 9 | high-pressure, high-temperature water jet |
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The most critical misconception: the second numeral is not a ranking
Up to and including 6, the tests build on one another: equipment that passes the water jet test also passes the splashing water test.
From `7` onwards, this no longer applies. A rating of IP67 does not imply that the device satisfies IP66. The tests are different: immersion tests against static water pressure, jet tests against dynamic pressure from one direction. An enclosure design may pass one test and fail the other.
This is not a technicality but a question of design: static and directed pressure place different loads on seals.
Where both are required, the manufacturer must mark both – such as IP66/IP67. A single designation covers only the test stated.
For procurement, this has a tangible consequence: if a system is to be washed down with a high-pressure cleaner after deployment, IP67 on its own is not sufficient evidence.
What the test actually evaluates
The test conditions are standardized, and they differ from real-world conditions.
Testing is performed with clean fresh water. Salt water, cleaning agents and chemically contaminated liquids are not part of the test.
The test for temporary immersion lasts 30 minutes. The water temperature may be only slightly below that of the device under test. The reason is physical: a warm device that enters cold water actively draws water in as the air inside cools. Exactly this situation – a device at operating temperature, cold rain – is the normal case in operation and is excluded in the test.
The standard also defines two supplementary letters for the water test that rarely appear in data sheets: M for testing with moving parts in motion, and S for testing with moving parts stationary. For a system with moving joints, this is a significant difference – a shaft seal behaves differently in motion than at rest. If the letter is missing, it is not apparent in which state the test was carried out.
`IP68` without stated conditions is not a specification. The standard defines neither depth nor duration for the numeral 8; both are agreed between manufacturer and user. A data sheet entry that only states IP68 leaves open what it refers to. Asking about it belongs in every technical clarification.
What an IP rating does not cover
The marking describes two properties. Everything else needs separate evidence.
- Mechanical impact resistance. This is covered by the IK code according to DIN EN 62262, which expresses impact energy in joules. It is stated separately and is usually missing entirely for mobile systems.
- Corrosion. Saline air, road salt and wastewater atmospheres attack enclosures, fasteners and connectors without any water ingress. This is demonstrated through salt spray testing, not through the IP code.
- Chemical resistance. Cleaning agents, oils and solvents act on seal materials. A seal that swells loses its function without this being visible from the outside.
- Condensation. A dust-tight enclosure can accumulate moisture inside through temperature changes. This is a known effect and the reason for pressure compensation elements – which in turn affect the water test.
- UV resistance of plastic parts and cable sheaths in continuous outdoor operation.
- Explosion protection. See Explosion protection and mobile robotics – recognising zones, determining limits.
What this means for mobile systems
For a permanently installed control cabinet, the IP rating is a largely stable property. For a system that is moved, opened and reconfigured, it is tied to conditions.
The degree of protection applies to the complete system in a defined state. Payload interfaces are usually sealed only with the cover in place or the payload connected. An open connector is an opening in the enclosure. Anyone who mounts a third-party camera or sensors moves the sealing to that interface – and with it the responsibility for it.
Exchangeable components are test items in their own right. A battery that can be exchanged in the field means a separation point with contacts. Its degree of protection when open, during the exchange and with soiled contact surfaces is a question of its own.
Peripheral equipment often has a lower degree of protection than the device itself. Charging stations, data interfaces and control units are frequently designed for indoor installation or protected outdoor installation, even when the device itself is specified for outdoor operation. For site planning, the lowest degree of protection in the system is decisive – not the highest.
The rating ages. After a repair, a fall or the replacement of an enclosure part, it only applies if the manufacturer or an authorized service provider has restored and confirmed the condition. Whether and at what intervals a leak test is intended is stated in the operating manual – and is a sensible item in the maintenance contract.
Checklist: ingress protection
- Complete specification including both numerals, not just "IP67"
- For cleaning with water jets: separate rating for the second numeral 5, 6 or 9
- For IP68: agreed depth and duration in writing
- State during the test: in motion or stationary
- Degree of protection of the payload interface when open and when occupied
- Degree of protection of the charging station, control unit and other peripherals
- Evidence of corrosion resistance where the environment requires it
- Requirements for a leak test after repair or a fall
- Responsibility for restoring the degree of protection after an intervention
This checklist will be offered as a download once the template exists.
Which degree of protection an individual model has, and the source supporting it, is recorded in the robot database. How it fits into the overall assessment of a system is covered in Inspection robots – a guide for operators.
Sources
- DIN EN 60529 – Degrees of protection provided by enclosures (IP Code) DIN Deutsches Institut für Normung / VDE accessed 16 October 2026
- IEC 60529 – Degrees of protection provided by enclosures (IP Code) International Electrotechnical Commission accessed 16 October 2026
- DIN EN 62262 – Degrees of protection provided by enclosures for electrical equipment against external mechanical impacts (IK code) DIN Deutsches Institut für Normung / VDE accessed 16 October 2026
- ISO 20653 – Road vehicles – Degrees of protection (IP code) International Organization for Standardization accessed 16 October 2026
Change log (1)
- 16 October 2026 Initial publication First publication of the English version.