What the two numerals mean
The IP code of IEC 60529 describes how well an enclosure keeps out solid objects and water. It has two numerals, sometimes followed by letters:
IP 6 7 (first numeral: solids · second numeral: water)
The first numeral runs from 0 to 6. Up to 4 it describes the size of objects kept out (from 50 mm, a hand, down to 1 mm, a wire); 5 is dust-protected, 6 is dust-tight. The second numeral runs from 0 to 9 and describes water from dripping (1, 2) through spraying and splashing (3, 4) and jets (5, 6) to immersion (7, 8) and high-pressure, high-temperature cleaning (9). An X means the property was not tested, as in IPX4.
The tests behind the numerals
Each numeral stands for a defined test. The ones that matter most for sensors:
- IPX5: 6.3 mm nozzle, 12.5 l/min, from 2.5 to 3 m, at least 3 minutes
- IPX6: 12.5 mm nozzle, 100 l/min, at least 3 minutes
- IPX7: 30 minutes immersed, the lowest point 1 m below the surface
- IPX8: conditions agreed between manufacturer and user, more severe than IPX7; a data sheet should state the depth and time, e.g. 10 m for 30 days
- IPX9 / IP69K: water at 80 °C and 8 to 10 MPa, 0.10 to 0.15 m from the nozzle, from four angles
Why IP68 does not include IP66
Up to second numeral 6, a code includes all lower ones: IP66 also passes IP65. Immersion is different. An enclosure that survives standing water may still let a powerful jet force water past a seal, so IEC 60529 states that 7 and 8 do not imply 5 or 6. Enclosures tested for both are dual-coded, e.g. IP66/IP68. The decoder flags this case and checks dual codes as a whole.
Worked example
A submersible level probe is marked IP68, and the site specification asks for IP65 because the head is hosed down:
- IP68 meets IP67 (8 is by definition more severe than 7)
- IP68 alone does not meet IP65: immersion does not include jets
- An IP66/IP68 probe meets both requirements
IP and NEMA
North American enclosures are rated to NEMA 250 types. NEMA publishes a one-way comparison: each type meets at least a certain IP code, for example NEMA 4 and 4X meet IP66 and NEMA 6P meets IP68. The reverse is not possible, because NEMA types also cover corrosion, icing, oil and gaskets aging, which IP codes do not test. Enter a NEMA type to see its IP equivalent, or an IP code to see which NEMA types also meet it.
Common mistakes
Assuming a higher number is always better. IP68 is not a superset of IP66, and IP69K says nothing about immersion.
Forgetting the cable entry. The rating applies to the enclosure as tested, with the specified cable gland and thread. An unsuitable gland or an unsealed process connection thread lowers the protection.
Taking IPX8 at face value. Without stated depth and duration, IPX8 can mean little more than IPX7.
Frequently asked questions
What do letters after the code mean?
A to D after the numerals state protection against access by a hand, finger, tool or wire. H, M, S and W are supplementary: high-voltage apparatus, water tested with parts moving or stationary, and suitability for specified weather.
Is IP69K the same as IPX9?
The tests are practically the same. IP69K comes from ISO 20653 (road vehicles, formerly DIN 40050-9); IPX9 was added to IEC 60529 by Amendment 2.
Does a higher IP rating make a device hazardous-area rated?
No. Ingress protection and explosion protection are separate; check the Ex marking with the Ex marking decoder.