A breakthrough for hazardous areas
A polyamide cable protection system which fulfils the Atex regulations

Cable protection is an inconspicuous but very important detail in system design and construction. After all, a defective cable can disable a complete system. PMA, a specialist in polyamide cable protection systems, has now developed a flexible polyamide system which fulfils the stringent requirements of the Atex directive and can therefore be recommended for applications in the process industry.

Cable protection systems prevent malfunction or complete breakdown of machines, vehicles and installations, avoiding potential financial losses through production stops and claims for compensation. Most common metal or polyamide cable conduits are suitable for this role, in particular cable protection systems made from polyamide have established and proven themselves through flexibility and mechanical strength, resistance to UV in outdoor applications, resistance to corrosion and, for a polyamide, a wide application temperature range. Exceptionally wide reaching consequences can result from cable damage in an area at risk of explosion. A damaged cable is a potential source of ignition which could lead to very grave accidents with serious results for equipment and personnel.

The high requirements upon the Cable Protection components in Ex-systems have up till now prevented the use of polyamide solutions. No system available on the market fulfilled the requirements of the standards behind the directive 94/9/EG (Atex 95). At the end of 2005 the Swiss cable protection manufacturer PMA presented the first flexible completely polyamide cable protection system approved for use in the Atex 137 defined zones 1 and 2 (gas/vapours) plus zones 21 und 22 (dust) according to directive 94/9/EG.
Generally a cable protection system should protect electrical cables and lines from mechanical influences such as chafing, compression, bending and impact, seal against water or any other fluid, as well as excluding weathering, UV radiation, chemical exposure and rodents.
For this role in machine, vehicle and installation building flexible or highly flexible corrugated polyamide conduits have established and proven themselves. Static, dynamic and even applications in robotics could be realised. Variations upon Polyamide 6, Polyamide 11 and Polyamide12 specially modified for the specific application environment have shown themselves to be best suited to fulfilling high and highest protection requirements.
High demands
In areas where through gases, fluids or finely distributed solid particles in combination with oxygen an explosive atmosphere can potentially occur there are for safety reasons strict requirements concerning the machines and components which may be used. For cable protection systems this means firstly more stringent requirements upon the system resistance to ingression of water, dust etc., to ageing at high temperature and to impact at low temperature. The latter provided the material engineers in the past with the greatest challenge. Secondly all materials used must be modified to ensure electrostatic discharge because polyamides tend towards the build up of electrostatic charge and can as such be a potentially igniting source in an explosion risk environment. If the surface resistance is below109 Ohms electrostatic charge which could otherwise build up through, for example, two surfaces rubbing together will be discharged via the earth connection of the cable protection system preventing igniting sparks. Only when a product can be proven to have all these characteristics, through testing of samples according to EN 60079-0 and EN 60079-7 (formerly EN 50014 and EN 50019), will it receive an Atex 95 approval.
Through the use of specially modified Polyamide 11 and Polyamide 12 raw materials combined with an optimal component geometry, for the first time polyamide cable protection systems can be built which fulfil these high requirements. The modified polyamide has a surface resistance between 106 and 108 Ohms to ensure no electrostatic build up. They are halogen and cadmium free, resistant against motor fuels, fats, oils, weak acids and bases, as well as other common solvents and do not corrode. The components are approved according to Atex 95 for use in the temperature range –20 °C to +85 °C so they are suitable for use under the most adverse conditions in indoor and outdoor applications. The product range includes in addition to the highly flexible corrugated conduit, numerous straight and elbow terminations, distributors and mountings for the conduit. A special connecting piece allows a simple connection from a rigid metal conduit to flexible polyamide. According to the required ingress protection specification the fittings are available with IP66 and IP68 ratings. The threads for the IP68 series are made from nickel plated brass.
Added value of flexibility
The flexible cable protection system offers not only assembly and configuration advantages but also substantial associated cost savings. Flexible corrugated conduit is quickly and easily formed around corners, so that time consuming assembly procedures, such as cutting to precise length and fitting corner parts are not necessary. The conduits can be cut with a standard knife or a special pair of scissors and attached very easily to a system by pushing them into the fittings. Re-opening of the connection is possible, but for safety reasons a screwdriver is necessary, it cannot be done purely by hand. The conduits have excellent resistance to reverse bending, withstanding more than four million cycles, making them extremely well suited to dynamic applications. Conventional cable protection systems for Ex-applications were unable to cover such use. The new Atex approved products are functionally equivalent to the standard PMA products which have been tried and tested in rail, machine and automation segments for 30 years now. This modified raw material product line allows the system to be used in critical, explosion endangered installations. These include for example, chemical installations, refineries, oil, gas and pharmaceutical plants, painting machines, mills and textile factories. But the new system is also suitable for use in the machines and installations used for the manufacture and handling of paper and cardboard.