CABLE GLANDS FOR HAZARDOUS AREAS
Sometimes regarded as a low priority component and often in practice the last thing to be considered when construction materials and cables are being sourced, Cable Glands are "safety critical" elements in the overall electrical system of any Hazardous Area plant or installation. Their importance should not be under estimated. After all, selection of the Cable Gland product that affords the best degree of long term environmental protection, will inevitably lead to fewer operational problems arising in service. On the other hand a 'fit for purpose' minimum standard option may well result in unavoidable costs being drained from future maintenance budgets, which far outweighs the apparent 'saving' generated in the initial selection process. Add to this the owner or operator's duty and responsibility in respect of Health and Safety and particularly in areas where there is a risk of explosion, the argument for getting it 'Right First Time' is a very strong one and is applicable to all electrical apparatus including Cable Glands.
There are clearly differences between product design standards in Europe and North America.
The examples given here, unless otherwise qualified, are based on the practice adopted in Europe.
Cable Glands for armoured cables which are certified for use on Flameproof Ex d Equipment require an inner seal that is i. Gas Tight and ii. Able to maintain the Explosion Protection integrity which will form the means of preventing transmission of explosion from within the equipment.
Typically an Ex d Cable Gland will have an Inner and Outer Seal which will provide a minimum environmental protection of IP66.
Ex d Cable Glands can be used in Zone 1 and Zone 2 (and Zones 21 and 22 subject to particulars of the product certification) Hazardous Areas and are generally used on Ex d, Ex e and Ex N equipment. However it is important to ensure that the Cable Gland is capable of maintaining the restricted breathing characteristics for certain types of apparatus in the Ex nR category.
Cable Glands for armoured cables which are certified for use on Ex 'e' equipment do not require the inclusion of an Inner Seal, although in practice some operators prefer to retain this feature for added protection against dirt and moisture migration. The fundamental requirements of Ex 'e' certified Cable Glands are that they shall maintain an IP rating of IP54 minimum (or IP64 in the case of Dust Hazards) and have an impact strength of 7Nm minimum.
Ex e Cable Glands can be used in Zone 1 and Zone 2 (and Zones 21 and 22 subject to particulars of the product certification) Hazardous Areas and are used on Ex e Apparatus and certain Ex d Equipment having an Increased Safety terminal chamber, usually designated with a code of protection Ex de. Caution should be used when selecting Ex e Cable Glands for Zone 2 certified Ex N Equipment as a Cable Gland with Outer Seal only may not be appropriate for that particular apparatus.
Cable Glands for unarmoured cables may be certified for use on both Flameproof Ex d and Increased Safety Ex e Equipment. However in practice some situations may restrict the use of unarmoured cables in Zone 1 Areas (and Zone 21) and hence Flameproof equipment, or in areas where there is any risk of mechanical damage. Many Cable Gland products can be supplied with 'Dual Certified' Ex d and Ex e status, although this is not always possible to provide with all types of Cable Gland.
Under IEC Standards (IEC 60079-0 & IEC 60079-1) three main types of cable glands exist for Explosive Atmospheres applications, for either armoured or non armoured cables.
|Form of Equipment Protection / Cable Type||Non-Armoured Cables||Armoured Cables|
|Increased Safety-Ex e (IEC 60079-7)|
|Flameproof-Ex d (IEC 60079-1)|
|Flameproof Compound Barrier – Ex d (IEC 60079-1)|
When it comes to Zone 2 equipment form of protection Type 'n', the picture is not so clear as it may first appear. As there are special requirements which apply to the sealing of cables entering form of protection type 'nR' (Restricted Breathing Enclosure) apparatus, it should not automatically be assumed that cable glands with Ex d or Ex e certification can be used.
IEC protection concepts Ex d, Ex e, Ex n
Cable Gland for Cables entering Ex e Apparatus
The Minimum Requirements for Ex e Cable Glands
- Impact Strength - 7 Nm,
- I.P. Rating - IP54 Gas / Vapour - IP6X Dust,
- Sealing Washer at Cable Entry Interface is Recommended,
- Single (Outer) Seal as a Minimum,
- Trend is to Use Double (Inner/Outer) Seal.
Note : Whilst the minimum Ingress Protection rating is said required to achieve Ex e certification under IEC 60079-7 is IP54, it should be considered that the cable gland is required to maintain the integrity of the equipment enclosure which is invariably higher.
It can also be noted that IEC 60079-14, section 11.3 states that threaded cable entry devices connected into threaded cable entry plates or enclosures of 6 mm or greater thickness need no additional sealing between the cable entry device and the entry plate or enclosure, providing the axis of the cable entry device is perpendicular to the external surface of the cable entry plate or enclosure.
However CMP Products recommends the use of a CMP Entry Thread Sealing Washer, which when installed at the cable entry interface, between the equipment enclosure and the cable entry device offers I.P. protection in excess of IP66. These components have been independently 3rd party tested in Ingress Protection tests to IEC 60529.
Cable Gland for Armoured Cables entering Ex d Apparatus
The Minimum Requirements for Ex d Cable Glands
- Screwed Entry Threads Must Maintain Flameproof Path,
- Minimum 5 Full Thread Engagement With Mating Equipment,
- Inner Seal Must be Flameproof & Gas Tight,
- Trend Has Been to Use Dual Certified Ex d / Ex e,
- Limitations Of Safe Use Usually Exist,
- Users Must Also Carefully Follow IEC 60079-14.
Cable Gland for Armoured Cables entering Ex n Apparatus
The Minimum Requirements for Ex n Cable Glands
- Cable Gland / Equipment Interface Seal is Essential,
- Restricted Breathing Enclosure Features Must be Maintained - Apparatus Maker Responsibility,
- Special Test Under IEC 60079-15 Applies For Ex nR Apparatus & Cable Entry,
- Some Flameproof Cable Glands Do Not Comply,
- Inner Seal Must be Air Tight in Two Directions.
Ex n apparatus was originally produced to early British Standards, e.g. BS 4533. Ex n cable glands were originally produced to British Standard BS 4121 (with Imperial threads) and later BS 6121 (with Metric threads), but this form of protection declined in popularity until 1990's when a new European Standard and subsequent IEC equivalent was developed and adopted globally. Unlike Flameproof Type d cable entry devices, IEC 60079-14 says very little about the measures required to be taken by the installer to ensure compatibility when sealing cables entering Restricted Breathing enclosures.