IP5X mandates limited, harmless dust ingress while IP6X requires absolute dust-tightness, both verified using standardized vacuum and duration tests.

The highest two degrees of the first characteristic numeral specifically address the penetration of dust. These levels require specialized testing using a dust chamber (Figure 2) and finely sifted talcum powder.

• IP5X (Dust-protected): Total exclusion of dust is not guaranteed. However, the dust that penetrates shall not accumulate in a quantity or location that interferes with the satisfactory operation of the apparatus or impairs safety. Crucially, dust should not deposit where it could lead to tracking along the creepage distances.
• IP6X (Dust-tight): This is the highest level, demanding no ingress of dust observable inside the enclosure at the end of the test.

The testing procedure depends on classifying the enclosure into one of two categories based on pressure differential:

• Category 1 Enclosures: These are enclosures where normal operation (e.g., thermal cycling) causes internal air pressure to drop below the surrounding atmosphere. During testing, a vacuum pump is used to maintain the pressure inside the enclosure below atmospheric pressure, drawing a volume of air 80 times the enclosure volume. The maximum depression shall not exceed 2 kPa (20 mbar). The test duration is either 2 hours (if the extraction rate is fast) or up to 8 hours (if the rate is slow). IP6X enclosures are always deemed Category 1, regardless of their actual working cycle.
• Category 2 Enclosures: These have no internal pressure difference. They are tested in the dust chamber without a vacuum connection for a fixed duration of 8 hours.

For IP5X, the relevant product standard specifies the enclosure category, otherwise Category 1 is assumed. For both levels, the test talcum powder must be fine enough to pass through a sieve with a nominal gap width of 75 µm.