IP66, IK10, and C5-M — what the designations actually mean

IP Code — Protection Against Access, Dust and Water

In IEC 60529, the code letters IP mean International Protection. The IP code indicates the degree of protection provided by an enclosure against access to hazardous parts, solid foreign objects and water. The standard applies to enclosures for electrical equipment within its scope. An IP code is read as two digits: (IEC 60529)

IP66 is commonly specified for street luminaires. A test result applies to the tested specimen under the stated test conditions; it does not by itself show how the degree of protection will be maintained during long-term operation.

What IP66 Does Not Test

• Thermal pumping: Temperature changes can create pressure variations inside the enclosure. The IP66 test does not assess long-term temperature cycling or condensation behaviour, so an IP66 result does not by itself rule out future moisture problems.
• Gasket ageing: Gaskets can change through ageing and environmental exposure. The IP66 designation does not by itself state how long sealing performance will be maintained under UV exposure, temperature cycling and field-maintenance conditions.
• Immersion: IPX7 covers temporary immersion under the conditions specified in IEC 60529. For IPX8, the test conditions are agreed between the manufacturer and user and must be more severe than those for IPX7. Water-jet protection and immersion protection are separate tests; where both are required, the documentation must show that both have been verified.

See Moisture, Condensation and Failure Modes for the full discussion of why IP class alone does not rule out moisture damage.

IK Rating — Mechanical Impact Resistance

The IK code is defined in IEC 62262:2002+A1:2021 and EN 62262:2002+A1:2021; the Swedish edition is SS-EN 62262:2022. It specifies resistance to mechanical impacts under defined test conditions, and the 2021 amendment defines IK11 at 50 J. The appropriate IK level depends on mounting height, accessibility, expected impact and procurement requirements. (IEC 62262)

IK10 specifies an impact energy of 20 J. For luminaires, the guidance in IEC TR 62696 uses three impacts on the point or points assessed as weakest. The test does not simulate long-term wear, vibration or all forms of vandalism. (IEC TR 62696)

C5-M and C5 — Legacy and Current Corrosivity Designations

ISO 12944-2:1998 used the categories C5-I for industrial and C5-M for marine atmospheric corrosivity. ISO 12944-2:2017 instead uses C5 for very high and CX for extreme atmospheric corrosivity. C5-M remains in use as a legacy industry designation but must not be confused with the categories in the current edition: (ISO 12944-2:2017)

ISO 9227 describes how salt-spray testing is performed but does not by itself determine the test duration or acceptance criteria for a particular product. ISO 12944-6 describes laboratory assessment of protective paint systems on steel structures within the standard’s scope. The results inform the selection of a coating system; they are not an exact prediction of service life. A C5-M claim therefore does not by itself show that 1000+ hours of salt-spray testing or a particular durability range has been verified; this must be stated in the actual test report for the specified system. (ISO 9227:2022)

C5-M, SMC, and Aluminium

Here there is an important distinction:

• Aluminium with C5-M coating: Aluminium oxide (spontaneous oxidation) provides some base protection, but heavy salt deposition on damaged paint areas accelerates corrosion. The coating system is critical.
• Composite: Glass-fibre-reinforced thermoset does not undergo metallic or electrochemical corrosion in the material itself and therefore needs no surface protection system against such corrosion.

See SMC, Aluminium and Cast Iron for a deeper comparison of housing material corrosion resistance.

What Municipalities Should Ask About

1. IP class + gasket properties: Require the manufacturer to disclose the gasket type (material, Shore hardness) and recommended replacement interval. An IP66 result at delivery does not by itself show that the degree of protection will be maintained after 10 years without maintenance.
2. IK class on the exposed surface: Require the test report to state whether the complete assembled luminaire or only a panel was tested, the mounting during the test, the tested points, the impact energy and method, and the specimen to which the rating applies.
3. C5-M/C5: request system-specific documentation. The documentation should state the standard and edition; tested substrate and surface preparation; complete coating system and dry-film thickness; corrosivity category and durability range; test methods, exposure durations and acceptance criteria; and the test specimen covered by the report. An independent or accredited report may be specified as a procurement requirement; ISO does not automatically require one.
4. Housing material and surface protection: For coastal installations, the housing material, surface treatment and the luminaire’s other exposed parts must be assessed together.
5. Combination of designations: Each claim — IP66, IK10 and C5-M/C5 — must be linked to the correct standard edition, test specimen and report. The designations do not automatically mean that three separate laboratory tests have been completed, and none simulates long-term combined field exposure.