IP ratings on protective cases: what the numbers mean and what a claim needs
IEC 60529 dust and water codes, why "waterproof" on a listing is not a rating, and the design details that decide whether a case keeps water out.
Short answer
- An IP code is two digits: the first for solid ingress and contact protection, the second for water.
- A gasketed lid keeps splash out and is genuinely useful, but that is a design feature, not an IP test.
- Gasket compression and its recovery after temperature cycling; the number and spacing of latches and whether they are adjustable; the flatness of the sealing face; the path of any cable or conduit entry; and the pressure-equalisation valve.
- Sealed cases change internal pressure with altitude and temperature.
The code itself
An IP code is two digits: the first for solid ingress and contact protection, the second for water. IP54 means limited dust ingress and splashing from any direction; IP67 means dust-tight and protected against immersion to 1 metre for 30 minutes; IP6K9K, where offered, covers high-pressure steam cleaning. The rating is a test outcome for a specific sample under specific conditions, not a property of a product line.
Why most listings do not have a rating
A gasketed lid keeps splash out and is genuinely useful, but that is a design feature, not an IP test. When a listing says "IP67" without a report, it is describing the shape of the gasket, not a result. Ask for the test report: the standard, the sample identification, the date, the lab, and whether the test was on a production sample or a prototype.
What actually determines the outcome
Gasket compression and its recovery after temperature cycling; the number and spacing of latches and whether they are adjustable; the flatness of the sealing face; the path of any cable or conduit entry; and the pressure-equalisation valve. A perfect shell with one un-rated cable gland is not an IP67 assembly.
Temperature, altitude and the valve
Sealed cases change internal pressure with altitude and temperature. Without a vent, a case can bulge a lid, leak past a gasket, or become impossible to open. A pressure-equalisation valve equalises air while resisting liquid, and it is the cheapest component that most buyers forget to specify.
A practical test plan
Define the worst realistic exposure — rain on a load bed, a dock splash, a dropped-in puddle — and test to that. A simple in-house check: fit the liner with a paper indicator, submerge to the depth and time you care about, and inspect. Then repeat after 50 open-close cycles, because latch wear, not moulding, is what degrades sealing over a product’s life.
Questions buyers ask
Is IP68 better than IP67?
Not automatically. The second digit of IP6x is defined by the manufacturer’s stated conditions and must be specified in writing. "IP68" without depth and duration is meaningless.
Do foam liners affect sealing?
Indirectly. A liner that pushes the payload against the lid plane can hold the gasket open. Specify liner thickness relative to the internal sealing dimension, not the visible cavity.