IP Ratings Explained: What IP65, IP66 and IP68 Actually Require
What the digits in IP65, IP66 and IP68 really test, why gaskets and cable glands decide the outcome, and where enclosures are commonly mislabelled.
IP ratings appear on almost every outdoor enclosure datasheet, and they are widely misunderstood. The two digits describe protection against solid objects and water, but the test conditions behind them are specific, and the rating applies to a complete assembly, not to a bare moulding. An enclosure that passes as a moulded part can fail once glands, gaskets and fasteners are fitted by someone in a hurry.
Reading the two digits
The first digit covers solids, from 0 (no protection) to 6 (dust-tight). The second covers water, from 0 to 9K. IP65 means dust-tight and protected against water jets from a nozzle from any direction. IP66 means dust-tight and protected against more powerful jets, tested at higher pressure and flow. IP68 means dust-tight and suitable for continuous immersion under conditions agreed between manufacturer and user; the standard does not define a single depth and duration, so a claim of IP68 without stated conditions is incomplete.
It is worth noting what the digits do not say. They do not describe corrosion resistance, UV stability, impact strength or the life of a gasket. Two enclosures can both carry IP66 and behave very differently after two years in coastal air.
How the water tests differ
The IP65 jet test uses a 6.3 mm nozzle at 12.5 litres per minute from a distance of about three metres for at least three minutes, directed at the most vulnerable surfaces. IP66 uses a 12.5 mm nozzle at 100 litres per minute from the same distance for at least three minutes. The higher flow and larger nozzle produce a much harder impact on seals, which is why a design that passes IP65 does not automatically pass IP66.
IP68 testing is agreed case by case. The manufacturer states a depth and duration, and the sample is immersed and then inspected for water ingress. Without those two numbers, the rating cannot be compared between products.
Gaskets, glands and assembly
Most field failures happen at interfaces. A moulded gasket groove that is clean and correctly sized will seal; the same groove with a moulding flash line, a twisted gasket or an over-tightened screw will not. Cable glands are the other weak point: a gland rated IP68 is only IP68 when matched to a cable of the correct diameter and tightened to the specified torque.
Fastener torque matters more than many assemblers expect. Uneven tightening distorts the lid and opens a gap on one side. For enclosures that will be opened for service, a captive screw design and a visible gasket seat help keep the seal repeatable.
Common mislabelling
Three mistakes recur. The first is quoting the moulding's rating as the assembled enclosure's rating. The second is assuming IP68 is simply "better" than IP66; for an enclosure that must be opened regularly, a well-designed IP66 with a replaceable gasket may be the more practical choice. The third is ignoring condensation. A sealed enclosure that breathes through a damaged gland can accumulate moisture from temperature cycling even without a direct jet, which is why breathers or desiccant are sometimes specified alongside the rating.
Ask for the test report, not just the label. Confirm the gasket material and its temperature range, check that the glands supplied match the cable schedule, and state the immersion conditions if IP68 is required.
One more point is often overlooked: pressure equalisation. A sealed enclosure heats during the day and cools at night. Without a breathable membrane, the pressure difference pulls air, and moisture, past the weakest seal. A membrane vent rated to the same IP level solves this without admitting liquid water. On coastal sites, specify stainless fasteners and a gasket material that resists salt fog; nitrile is a reasonable default, while silicone suits wider temperature swings. Record the tightening torque on the assembly drawing so service replacements do not undo the rating.
Our injection moulding service produces enclosure halves with controlled gasket grooves and documented first-article inspection. Send the IP target and the cable schedule, and we will confirm the sealing arrangement before tooling starts.
