What does IP66 on an Ex label have to do with explosion protection?
Abstract
IP66 means dust-tight and protected against powerful water jets (IEC 60529). It is not explosion protection and says nothing about gas. But several protection concepts depend on a minimum IP rating, for example Ex e (IP54 with bare live parts) and Ex t (IP5X or IP6X).
On its own, nothing: IP66 is an ingress protection rating under IEC 60529. The first 6 means dust-tight, the second 6 means protected against powerful water jets. It does not make equipment explosion-protected and it says nothing about gas. It still matters, because several types of protection only work if the enclosure keeps out dust and water, and their standards set a minimum IP rating.
Short answer
- IP66 = dust-tight (6) + powerful water jets (6) in the IP code of IEC 60529. IP tests use dust and water, never gas.
- An IP66 enclosure is not suitable for a hazardous area unless it also carries an Ex marking for the zone. See the related question on IP65 in Zone 21.
- Some concepts rely on IP. Increased safety (Ex e) needs at least IP54 for enclosures with bare live parts; dust protection by enclosure (Ex t) needs IP5X or IP6X by dust group and level; pressurisation (Ex p) mostly IP4X.
- For other concepts IP is for the environment. A flameproof (Ex d) enclosure contains an explosion through its flamepaths; its IP rating protects the contents from weather and washdown.
- Where Ex safety depends on IP, IEC 60079-0 has the IP test done after the impact test (and, for non-metallic enclosures, after the thermal endurance tests), so the rating is proven on a stressed enclosure.
Reading the two digits
| Digit | Value | Meaning (IEC 60529) |
|---|---|---|
| First (solids, dust) | 5 | Dust-protected: some dust may enter, not enough to interfere with operation or safety |
| First | 6 | Dust-tight: no ingress of dust |
| Second (water) | 4 | Splashing water from any direction |
| Second | 5 | Water jets |
| Second | 6 | Powerful water jets |
| Second | 7 | Temporary immersion |
An X in place of a digit, as in IP6X, means that characteristic is not specified. The dust-related Ex requirements are therefore often written as IP5X or IP6X.
Where the IP rating is part of the explosion protection
| Type of protection | Minimum degree of protection | Why |
|---|---|---|
| Ex e, eb and ec (IEC 60079-7) | IP54 with bare live parts; IP44 with insulated live parts only (lower values only with an X certificate and a clean location) | Dust and moisture would erode creepage and clearance distances, the core of the concept |
| Ex t, dust (IEC 60079-31, as summarised by NSW TestSafe) | IIIC: IP6X for ta, tb and tc. IIIB: IP6X for ta and tb, IP5X for tc. IIIA: IP6X for ta, IP5X for tb and tc | The enclosure itself is the protection: dust must not reach ignition sources inside |
| Ex p (IEC 60079-2:2014) | IP4X for pxb, pyb and pzc with indicator; IP3X for pzc with alarm | The enclosure must hold the overpressure and keep out objects |
| Ex i (IEC 60079-11) | Often IP20, or IP54 where reduced separations rely on pollution degree 2; the certificate states what applies | Separation distances are protected from dust and moisture |
| Ex d (IEC 60079-1) | No IP rating for the flameproof principle itself | Flamepaths cool escaping gases; gaskets for IP must follow the standard's rules |
IEC 60079-7 notes explicitly that the degree of protection requirements of general industrial standards are not applied directly to Ex equipment. The 2024 edition of IEC 60079-14 adds an informative annex listing the minimum IP code for each type of protection, which installers can use as a cross-check.
Practical case: choosing between two junction boxes
A buyer compares two boxes for a Zone 1 offshore deck that is washed down with hoses. Box A is an industrial box rated IP66 with no Ex marking. Box B is marked Ex eb IIC T6 Gb and IP66. Only box B can go into Zone 1: its IP rating is part of an Ex certificate, and the increased safety concept depends on it. Box A is weather-proof but not explosion-protected. For Box B, the IP rating holds only while every cable gland and blanking plug also maintains it, which is why Ex e certificates often name the required IP rating of entry devices as a condition.
Common mistakes
- "IP66 means explosion-proof." It means dust and water resistance. Gas can enter any IP-rated enclosure through seals and breathing.
- Using an IP6X enclosure without an Ex t marking in Zone 21 or 22. Ex t also limits surface temperature and is tested to Ex rules.
- Losing the IP rating at installation: unsealed glands, missing O-rings, unused entries left open, damaged lid gaskets.
- Adding silicone or gaskets to Ex d flamepaths to improve IP. Only what the certificate and standard allow may be used.
Related on excodex
- How to read an Ex marking: decoding II 2 G Ex db IIC T4 Gb step by step
- Increased safety (Ex e): preventing sparks, arcs and hot spots
- Is an IP65 enclosure acceptable in Zone 21?
- Is an Ex d enclosure gas-tight?
- Can you paint or seal Ex d flamepath joints?
Standards and further reading
- IEC 60529, degrees of protection provided by enclosures (IP code), public copy of the 2013 consolidated edition: law.resource.org (PDF)
- IEC 60079-7, increased safety "e", degrees of protection (public copy of 2015): law.resource.org (PDF)
- IEC 60079-11, intrinsic safety "i", enclosures (public copy of 2011; edition 7, 2023, is current): law.resource.org (PDF)
- IEC 60079-2:2014, pressurised enclosures "p", design criteria table: law.resource.org (PDF)
- IEC 60079-0, test sequence for enclosures (public copy of 2004): law.resource.org (PDF)
- IEC 60079-31:2022, dust ignition protection by enclosure "t"; NSW TestSafe summary of its IP requirements: nsw.gov.au
- IEC 60079-14:2024, informative annex on minimum IP code by type of protection (contents in the preview): standards.iteh.ai (PDF)
This article is general technical information prepared by the excodex editorial team. It does not replace the applicable standards, the equipment certificates and instructions, national regulations or the assessment of a competent person.