Understanding IP ratings for connectors

"IP67" is one of the most frequently quoted values on a connector datasheet and one of the most frequently misread. The IP code, defined in IEC 60529, classifies the protection an enclosure provides against access to hazardous parts, ingress of solid foreign objects and ingress of water — each verified by a specific, standardised test. Applied to connectors, the code answers a narrow question under narrow conditions. This article explains how the code is built, what the tests involve, how mated and unmated ratings differ, where ISO 20653 and the K suffix come in, and which risks the code does not address at all.

How the IP code is built

The code consists of the letters IP, a first characteristic numeral for solid objects, a second characteristic numeral for water, and optionally an additional and a supplementary letter. Where a numeral is not specified, it is replaced by X: IPX7 states protection against temporary immersion and makes no claim about solids. IEC 60529 requires degrees of protection to be specified by the numeral, not by paraphrases such as "waterproof".

Additional and supplementary letters

An optional additional letter (A to D) states protection of persons against access to hazardous parts with the back of the hand, a finger, a tool or a wire, where that protection is higher than the first numeral implies. Supplementary letters (H, M, S, W) carry information defined in product standards, for example whether moving parts were in motion during the water test. On connector datasheets these letters are uncommon; the two numerals carry the information that matters.

Reading the numbers correctly

Two rules in IEC 60529 cause most misreadings. Up to and including numeral 6, a higher water numeral implies compliance with all lower ones: an IPX6 enclosure also meets IPX5 and IPX4. Above 6 that chain breaks. An enclosure marked only IPX7 or IPX8 is considered unsuitable for water jets, and one marked only IPX9 is not claimed to withstand immersion. Where an enclosure meets several, the standard requires multiple coding, such as IPX6/IPX7 or IPX5/IPX8/IPX9.

The acceptance criterion is also narrower than many readers assume. IEC 60529 does not demand that no water enters. In general, any water that has entered must not interfere with correct operation or impair safety, must not deposit on insulation where it could lead to tracking along creepage distances, must not reach live parts not designed to operate wet, and must not accumulate near or enter the cable. The relevant product standard or technical committee can define the permitted amount and any dielectric test. A connector datasheet that states which criteria were applied is more informative than one that states the code alone.

Mated, unmated and capped: the state behind the rating

A connector is not one enclosure but two halves that form an enclosure when mated. Its IP code therefore depends on the state in which it was tested, and a well-written datasheet says which:

• Mated — plug and receptacle coupled, coupling nut or latch fully engaged. This is the usual basis for an IP67 or IP68 claim on a circular industrial connector.
• Unmated with protective cap — the open interface closed by the manufacturer's cap or dust cover. The cap is part of the tested configuration and has to be fitted in service.
• Unmated, open — some fixed connectors are sealed behind the interface (for example by potting or a glass-to-metal seal), so that the device behind the panel stays protected even when nothing is plugged in. This is a design feature that must be stated explicitly.
• Panel interface — for a fixed connector, the rating also depends on the panel seal or O-ring, panel thickness, cut-out and mounting torque specified by the manufacturer.

For a cable connector, the rear end matters just as much as the mating face. A cable gland or grommet seals only within its specified cable outer diameter range and only with a round, undamaged jacket. A multi-conductor cable can also carry water along its interstices into a connector that is itself perfectly tight; this is one reason why moulded cable assemblies often perform better than field-wired connectors in wet locations.

ISO 20653 and the K codes for road vehicles

Road-vehicle equipment is usually specified to ISO 20653, Road vehicles — Degrees of protection (IP code) — Protection of electrical equipment against foreign objects, water and access (current edition 2023). It follows the structure of IEC 60529 but adds codes with the suffix K for conditions specific to vehicles, such as IP5K and IP6K for dust and IPX4K, IPX6K and IPX9K for water with increased pressure. IPX9K, which originated in the German standard DIN 40050-9 before ISO 20653 took it over, describes hot, high-pressure water jets at close range and is widely used outside the automotive sector — in food processing and agricultural machinery, for example — as shorthand for washdown resistance.

Because IEC 60529 now contains an IPX9 test with a similar intent, it is worth checking which standard a datasheet refers to. IPX9 under IEC 60529 and IPX9K under ISO 20653 are similar but not interchangeable references; a requirement written against one should be verified against the test report for that standard. Vehicle manufacturers frequently add their own test specifications on top, including combined tests such as thermal shock followed by immersion. The article on reliable connectivity in automotive applications covers this context.

What an IP rating does not cover

An IP code is a statement about ingress under specified test conditions at the time of the test. Several properties that decide whether a sealed connector survives in the field lie outside it:

• Temperature and thermal cycling — seals harden at low temperature and take a compression set at high temperature; repeated cycling can pump moist air in through any imperfect interface.
• Chemical resistance — oils, fuels, coolants, cleaning agents and disinfectants can swell, crack or soften seals, housings and cable jackets. This is assessed with material data and separate tests.
• UV and weathering — outdoor exposure degrades many elastomers and plastics over time.
• Ageing and mating cycles — a seal that passed when new may not after hundreds of mating cycles or years of compression. IP tests are normally done on new samples.
• Pressure differences and depth — continuous immersion beyond the stated IP68 conditions, or pressure on the enclosure from other causes, is not covered.
• Vibration and mechanical damage — a test on a static sample does not show whether the seal holds when the cable is loaded or the connector vibrates.
• Equivalence with other systems — North American enclosure types under NEMA 250 include conditions such as corrosion and icing, and are not directly interchangeable with IP codes.

Specifying and verifying an IP requirement

A useful IP requirement in a specification states more than two digits. It names the standard (IEC 60529 or ISO 20653), the code including any multiple coding, the state (mated, unmated with cap, unmated open), the mounting conditions for panel connectors, and, for IPX8, the depth and duration. Exposure that the code does not cover — chemicals, temperature range, UV — is listed separately. When comparing datasheets, check that the claimed code was obtained in the same configuration that will be used, and ask for the test conditions where they are not stated. The guide on understanding connector datasheets lists further points to check.

Sealing is rarely the only environmental requirement. The harsh-environment connectivity overview describes how it is combined with temperature, vibration and chemical resistance in practice.