Why Should You Specify Cable Glands?
How often have we heard:-
"We don't specify Cable Glands, as long as they have the relevant certification then it must be fit for purpose. We leave it to contractor to sort out. We are too busy concentrating on the high value, long lead time items to bother about such an insignificant value product.
In a recent paper presented at the Hazard Ex conference by a Senior Manager of CENELEC Standards Inspections, it was stated, "Resources should be directed at eliminating the following common faults:
- Unauthorised modifications.
- badly made-off or unsuitable cable entry devices.
It went on to say that out of these three factors, the most common fault was bad installation of Cable Glands. The paper was specifically referring to maintenance procedures, but this could equally be applied to new installations.
Incorrect specification and installation combined with the lack of ability to inspect the Cable Gland in it's operable condition can cause equipment failure and corrosion of cable armour and braid. The safety risks inherent in this is incalculable, as is the consequential loss of production.
This statement alone should be enough reason why specification of Cable Glands is an important decision. Just relying on the fact that a Cable Gland has a certificate "fit for purpose" is not enough.
So What Should You Take Into Account When Specifying The Cable Gland?
Certification and Selection
Of course, it is vital that the correct Cable Gland is selected and is certified as appropriate for the hazardous area in which it is to be used. We provide technical information in our Cable Gland catalogue and also supply a Cable Gland selection software application to take the specifier step-by-step through the process of selection. If still in doubt our Technical Department has a team of experienced engineers to assist. But just relying on a Cable Gland that is certified for the type of protection that is required (e.g. "fit for purpose") is not enough.
Ingress Of Moisture
One of the most important features of a Cable Gland is elimination of moisture ingress, not only into the equipment, but also into the armour clamping area of the Cable Gland itself. Water ingress into this area has been shown to cause catastrophic corrosion of cable armour and braids, with the associated costs of new cabling and downtime. IP ratings give a guide to protection of water and dust ingress into the equipment but not necessarily into the Cable Gland itself.
In 1991 Shell UK recognised that IP ratings are not necessarily sufficient to meet the harsh conditions found in many hazardous area installations and developed a far more demanding test DTS01 to eliminate water ingress under thermal cycling and deluge conditions. We have taken Shell's DTS01 test one step further and our DTS01 test certificate is extended to show no water ingress into the armour clamping area of the Cable Gland when fitted with a deluge seal. This is clearly an issue when specifying Cable Glands. Not all Cable Gland manufacturers test certificates cover ingress protection into the armour clamping area, nor do they cover the full operating temperature range for which they have been certified for use.
Why Should You Specify Cable Glands?
Cable Gland seals perform two functions:
- Prevents the products of an explosion reaching the outside atmosphere if an explosion occurs inside the enclosure.
- Stops water and dust ingress into the equipment and Cable Gland.
Various seal materials are used by different Cable Gland manufacturers, but in general they fall into two categories:
- Thermoset (TSE) These materials are cross-linked (vulcanised) during the moulding process with the application of heat and pressure. Once formed, they will not 'melt' and will exhibit optimum sealing properties over a wide range of temperatures.
- Thermoplastic (TPE) Although much cheaper to manufacture than TSE seals they 'melt' when heated and their sealing properties deteriorate as operating temperatures increase. Ideal for appliance feet, soft touch knobs and handles, they are not recommended for critical sealing applications.
TSE's on the other hand, are far more suitable for Cable Gland seals and are the only materials used by Hawke International in our range of compression and diaphragm Cable Gland seals. TSE's have better elastic properties over a wider range of temperatures, e.g.:
Compression set (recovery from deformation), the test is done usually at elevated temperatures and a test piece is squashed in a clamp by 25% of it's thickness, left in an oven for 3 days, at the end of which the sample is left to recover at ambient temperature. The difference between the original thickness and the new thickness (the ‘set’) is expressed as a percentage of the amount it was squashed by - a good TSE will show a compression set % of less than a 3rd of that shown by even the best TPE.
The ageing resistance of TSE's is better, particularly ozone, UV, oxidisation resistance and ‘weathering’ resistance. The chemical and oil resistance of TSE's can be infinitely better. The temperature resistance of TSE's is much better. For example, silicone TSE (used in Hawke's rear seals and in the 453/Universal diaphragm seal) has a maximum intermittent operating temperature of 300°C, whereas most TPE's soften appreciably at 100°C. Silicone will operate effectively at -60°C, whereas the best TPE works at -40°C. Flame resistance is better, silicone has the additional benefit of being low smoke and fume and zero halogen.
Cable Tolerances And Construction
Cable costs are significant in a hazardous area installation and we have seen moves to reduce costs by reducing specification and tolerances of the cables. Hawke International Cable Glands employ a rear sealing system with an extremely wide tolerance range, which takes into consideration variation in cable diameters along it's length and does away with the need to specify Cable Glands with special outer seals.
There are also requirements for some cables to be flame-resistant or flame retardant in accordance with IEC 60331 and IEC 60332. Many of these cables exhibit ‘cold flow’ of the inner sheath bedding. That is, the material will flow away from pressure applied to it, such as that of a Cable Gland inner seal of the compression or displacement type, hence creating an inefficient seal. The code of practice EN 60079-14 : 1997 / IEC 60079-14 : 1996 Clause 9.1.3 notes clearly states that a Cable Gland employing a compression (displacement) seal should not be used on cable exhibiting "cold flow characteristics". Hawke's 501/453/Universal Cable Gland uses a diaphragm inner seal that complies with this requirement in the code of practice, in that it exerts minimal pressure on the cables inner sheath. It does not cause ‘cold flow’ but maintains IP and explosion requirements.
Why Should You Specify Cable Glands?
Only training of the Cable Gland installer in the correct practice of installation can ensure that the Cable Gland will function correctly. Most reputable contractors ensure that their personnel have been fully trained and in many cases, it is a requirement that they hold a certificate from a recognised training authority such as CompEx. However, in some regions of the world, this is not so stringent, therefore it is important that the Cable Gland selected has been designed with ease of installation in mind, that every Cable Gland comes with detailed installation instructions and is easy to inspect at each stage of the installation operation. We have designed our Cable Glands with minimum components, ease, speed and simplicity of installation.
Safety Through Inspectability
Safety is of prime importance on hazardous area installations. Safety depends on many factors, some of which have already been discussed. Inspectability of equipment also plays a key part in safety. Can all the safety features of the Cable Gland be inspected, preferably easily? We have developed Cable Glands that answer Yes to this question. All our Cable Glands can be easily disassembled to allow visual inspection of the armour clamping arrangement. In addition the 501/453/Universal allows inspection of the inner seal on the cable sheath and the ICG 653/ Universal in the only barrier Cable Gland on the market that allows full inspection and if necessary, repair of the cured compound without destroying the Cable Gland. And finally the rear sealing arrangement and deluge seal can be inspected in their operable position.
Why You Should Specify Cable Glands
If you are interested in safety, reliability and the lowest lifetime cost through reduced downtime and loss of production of your plant, then you should take the time to consider specifying the features you require from your Cable Gland.
In summary, what key features during specification of Cable Glands should you be considering?
The most common fault experienced on hazardous area installations is incorrect selection and bad installation of Cable Glands.
- Will a Cable Gland that is certified "fit for purpose" meet all your requirements?
- There are necessary features that are not covered in the certification process. Does the Cable Gland meet your requirements for ingress of dust and moisture?
- Does it have a test certificate covering the deluge requirements of DTS01 for ingress into the equipment and into the armour clamping arrangement of the Cable Gland?
- Will the Cable Gland seals give long life and protection from water ingress under the typical heat cycling and operational conditions on site?
- Are they produced from the best Thermoset (TSE) material?
- Will the Cable Gland sealing range cope with the cable diameter tolerances without the need for special seals?
- Is the Cable Gland suitable for use on cables that exhibit ‘cold flow’ characteristics and in line with the code of practice BS EN 60079-14 1997/IEC 60079-14 1996 Clause 9.1.3?
- Is the Cable Gland fast and easy to install with minimum parts and clear assembly instructions?
- Will the Cable Gland enhance safety on your site through ease of inspection?
Careful consideration should be paid to these issues as they are not taken into consideration during certification. A certificate does not mean they are fit for your purpose. Correct selection and specification of Cable Glands will reduce costs during initial installation and throughout the life of the installation.