Can silicone sealant be used to improve the IP rating of Ex equipment?
Abstract
Generally no. Setting silicone sealant must never go on a flameproof joint, must not replace certified gaskets or gland seals, and silicone vapour can poison catalytic gas detectors. Fix the cause of water or dust ingress with the manufacturer's parts instead.
Generally no. A bead of setting silicone sealant is not a certified part of any Ex enclosure: on a flameproof joint it is forbidden, around an Ex e or Ex t cover it replaces the tested gasket with an untested one, and in a cable entry it does not replace the gland seal. Silicone vapour also poisons catalytic gas detectors. When water or dust gets in, find and fix the cause with the parts the manufacturer specifies.
Short answer
- Flameproof (Ex d) joints: no sealant and no gasket unless the manufacturer's documentation specifies one. Where the documentation is silent, only non-setting grease or anti-corrosion agents without evaporating solvents may be used on the joint faces (IEC 60079-14).
- Ex e, Ex t and other enclosures where IP is part of the protection: the IP rating comes from the certified design and its gaskets. Damaged gaskets are replaced, not covered with sealant.
- Cable entries: a sealing washer or thread sealant between gland and enclosure is acceptable where needed to reach the required IP, if it does not reduce thread engagement or the earth path. It does not replace the gland's own seal on the cable.
- Gas detection nearby: silicones are listed in IEC 60079-29-2 among substances that can permanently poison catalytic sensors.
- Unapproved additions are an "unauthorized modification" finding in IEC 60079-17 inspection schedules.
Why sealant on a flamepath is dangerous
A flameproof enclosure does not keep gas out. It lets an internal explosion happen and cools the escaping gases through narrow, long joints whose gaps are set by the certificate. A layer of sealant that hardens in the joint can hold the faces apart and widen the gap. It can also bond the cover so that the joint is damaged when someone forces it open, or leave a film that traps moisture and causes corrosion that nobody sees.
IEC 60079-14 therefore allows gaskets on flameproof joints only when the manufacturer's documentation specifies them, forbids painting the joint, and allows only non-setting grease or solvent-free anti-corrosion agents where the documentation says nothing about joint protection. Its note says silicone-based greases are often suitable for this purpose, with care near gas detectors, and that the grease must stay non-setting so the joint faces can be separated later. Threaded entries into Ex d enclosures may also take grease, but only a non-setting, non-metallic, non-combustible one that keeps the earthing between the parts.
Grease and sealant are not the same thing: a non-setting grease stays soft and can be wiped off at the next detailed inspection; a silicone sealant cures into a rubber layer.
Why sealant does not give a valid IP rating
For types of protection such as increased safety (Ex e) and protection by enclosure (Ex t), the degree of protection is part of the explosion protection itself: it keeps out water and dust that could cause tracking, arcing or ignition inside the enclosure. The certified IP was proven by test with the specified gaskets, cover screws and entry arrangement. A sealant bead applied on site has not been tested for adhesion, ageing, temperature range or chemical resistance, hides the real gasket condition and may stop the cover being opened for inspection without damage.
IEC 60079-17 requires that the integrity of the type of protection is maintained during remedial work, that replacement parts follow the safety documentation, and that damaged gaskets are replaced. Alterations that affect safety need authorisation, and repairs follow IEC 60079-19.
What to do instead
| Cause of ingress | Correct fix |
|---|---|
| Hardened, torn or missing gasket | Fit the manufacturer's replacement gasket |
| Cover screws loose or missing | Fit the correct screws and tighten to the instructions |
| Cable outside the gland's sealing range | Fit a gland sized for the cable |
| Unused entry left open or with a dust plug | Fit a certified blanking element |
| Condensation inside | Use a certified breather or drain if the equipment allows it |
| Equipment IP too low for the location | Replace with equipment of suitable IP, or shield it from direct jets |
Example: A technician on a washdown platform finds water in an Ex e terminal box and plans to run silicone around the lid. The inspection instead finds a flattened lid gasket and one gland on a cable below its sealing range. The gasket is replaced with the manufacturer's part and the gland with the correct size; the box passes a close inspection, and no sealant is needed.
Common mistakes
- Treating flamepath grease as permission for sealant. Only non-setting grease or solvent-free agents are acceptable, and only within the manufacturer's instructions.
- Sealing over a gland instead of fixing it. The seal on the cable is part of the certified entry; sealant around it is not.
- Using silicone near catalytic detectors. IEC 60079-29-2 lists silicones (in adhesives, waterproofing agents, release agents and some greases) among the substances that permanently reduce the sensitivity of catalytic sensors, so a detector can read low, and it calls for frequent sensitivity checks wherever such poisons may be present.
- Forgetting that inspectors must see the gasket. A sealed cover hides the evidence the next detailed inspection needs.
Related on excodex
- Common Ex inspection findings and how to fix them
- Cable glands for hazardous areas: barrier glands, compound glands and selection
- Do cable glands need to match the IP rating of the enclosure?
- Is corrosion on a flameproof flamepath a reason to take equipment out of service?
- Catalytic (pellistor) vs infrared flammable gas detectors
Standards and further reading
- IEC 60079-14:2024, electrical installations design, selection and installation, with clauses on protective coating of Ex equipment and protection of flamepaths (preview): cdn.standards.iteh.ai; 2007 text on protection of flameproof joints and cable entries (AS/NZS 60079.14:2009): archive.org
- IEC 60079-17, inspection and maintenance of electrical installations (IS/IEC 60079-17:2007 text): law.resource.org
- IEC 60079-29-2, selection, installation, use and maintenance of gas detectors (IS/IEC 60079-29-2:2007 text, catalytic sensor poisoning): law.resource.org
- IEC 60079-1, flameproof enclosures "d", and IEC 60079-7, increased safety "e" (construction requirements behind the joint and IP rules).
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.