Potential explosive atmospheres exist when a mixture of air gas, vapour, mist, or dust combine in a way that can ignite under certain operating conditions. It is these potentially explosive atmospheres which products falling under the ATEX Directive 2014/34/EU are designed for.
The directive defines not only the essential health but also the safety requirements and conformity assessment procedures, to be applied before products are placed on the market. Products that do not meet the ATEX Directive CE and Ex Mark cannot be marked as doing so.
ATEX rated equipment covers a wide range of products, including those used on fixed offshore platforms, petrochemical plants, mines, flour mills, amongst others. With such volatile gases and dust, these industries demand the very highest levels of safety from products they use in these areas. Within these sectors, products and equipment must comply within ATEX Standard (driven by EU law) or IECEx (a voluntarily Global certification scheme).
Exd Cable systems
IECEX explains how specialist cables such as fire-resistant cables must be used in certain Ex applications. The industry is fully aware of the precautions required when terminating cables for use in hazardous areas. Expensive fittings, epoxies and conduits all add to the time and cost of installation. Add the uncertainty the cable must be carried out in a manner that prevents tensile stress on these terminations only adds to the risk factor.
The recognised risks and costs associated with product failure result in greater detail and increased research being done into a cables true operation, Mineral Insulated Cables (MIC) may often be overlooked.
MIC has been in use commercially since 1937. From a fire performance perspective, it has not been surpassed by any other cable system. But did you know that if you combine a mineral insulated cable with an Exd rated cable gland you can achieve a hazardous area cable system suitable for zones 1 & 2 in one easy installation? Fitted with a fully approved cable gland there is no additional conduit needed or waiting for hours at a time for resins to cure. Consequently, Exd installations can be achieved in less than 10 minutes.
How does it work?
MIC cable has a unique copper sheath for its protection meaning it has its own fireproof conduit. Mineral Cables can survive temperatures in excess of 1000C for hours whilst undergoing direct impact and exposure to water pressure in excess of any current British Standard. The continuous operating temperatures of cables are often a key factor in selection decisions. A bare mineral insulated cable can work continuously up to 250C, far more than any other polymeric fire-resistant cable.
BS / IEC 60702-1 (the manufacturing standard for mineral insulated cables) states that each cable size must be manufactured to within 0.05mm in diameter. The insulation used in the construction of mineral insulated cable can be supplied by some manufacturers with highly compressed hand-fed magnesium oxide. This bespoke construction stops liquids and gas flowing through the cable. These extreme tolerances make the mineral cable a perfect candidate to create water, air and dust-tight seal with a fully approved mineral cable gland.
Each bespoke brass cable gland is precisely manufactured to match to a cable diameter. Once the lock nut is tightened the compression ring inside the gland clamps around the copper cable sheath. If a manufacturer holds the correct approvals the gland will also have a minimum of eight full threads for entry into Exd approved housing. With the correct approval MIC cable gland systems are permitted to be used in zone 1 & zone 2 locations and a complete Exd cable system is formed with multiple flame quench paths.
A newer type of Mineral Cable has seen growth in recent years. Popular in Asia, a twisted conductor mineral insulated cable provides greatly increased EMI performance. This specialist cable not only looks the same at its non-twisted counterpart but physically retains the same compact dimensions, meaning even greater performance with no compromise to size.
As safety and detection systems become increasingly complex, so does the demands placed on the cable feeding them grow. Mineral Cable in twisted form offers all its traditional benefits in terms of explosion-proof, gas resistant, dustproof and fire resistance, mechanical strength and now even higher levels of EMI without the need for additional screening and the associated cost and installation.
Mineral insulated cable offers so many inherent safety and fire-resistant advantages over soft skin polymeric fire-resistant cables. The following points summarise the clear advantages.
Mineral Insulated Cable – The Key Facts:
- MIC cable systems are significantly more cost-effective by up to 85% when compared to similar-sized Cable, Conduit, Exd connectors, and other gland systems.
- MIC cable systems are significantly less complex in component form and therefore less time consuming to install offering savings to installers and maintenance contractors.
- MIC cable can operate at a continuous temperature of 250o C, significantly higher than other cable types.
- MIC will withstand and still deliver load when compressed by 65% of its original outer diameter providing excellent resistance to impact and speedy maintenance inspections compared to hidden cables.
- MIC systems offer designers, engineers and installers the chance to maximise available space with MIC cable sizes with diameters being much smaller than other systems or products.
- You can find manufacturers of MIC cable systems offering a 30-year minimum lifetime warranty when installed by trained installers.
- Mineral Insulated Cable is totally inorganic and silicone-free.
- In most environments MIC cable manufactured as copper and MgO will not deteriorate and is a non-aging product.
As the only UK manufacturer of mineral insulated cables Wrexham Mineral Cables (WMC) offer the full range of mineral insulated cables including twisted. Established in 1989 they have supplied tens of millions of EX-rated cable glands to hazardous area environments around the world. In January 2018 they gained Dubai Civil Defence Approval with their local partners Solas Safety & Fire Protection Services. They also offer a 30-year warranty.
WMC has held ATEX approval since 1992. Their ring-type glands are specifically approved for apparatus (type of protection ‘d’) Zones 1 & 2, Groups IIA, IIB and IIC. Along with apparatus (type of protection T) zones 20, 21 & 22, groups IIIA, IIIB & IIIC. In compliance with EN 60079-0: 2012 / A11:2013, EN 60079-1:2014 and EN 60079-31:2014 under SIRA License SIRA02ATEX1305X
Steve Williams Commercial Manager of Wrexham Mineral Cables said, “The Exd cable system supplied by Wrexham Mineral Cables is manufactured by highly skilled personnel with the strictest of tolerances, process control is absolutely paramount. The use of high-quality raw materials, a 30-year-old Quality management System with zero in-field failures have made us market leaders in fire-resistant and Ex rated cable systems.”
He went on to say: “Momentum grows for more stringent inspections on buildings and cable systems. These inspections are not only within hazardous areas but all buildings supplying critical circuits. From our own investigations, we have found It can prove extremely difficult to inspect cables that are either buried in walls or placed in conduits. Mineral Insulated Cable can be surface mounted, has its own “built-in conduit”, will not degrade unlike polymeric cables and Inspection can take seconds.”
For more information, go to http://www.wrexhammineralcables.com/categories
About the Author
Steve Williams is Commercial Manager, Wrexham Mineral Cables Ltd.
