Efficient connections for the Ex zone
Howard Forryan argues the case for the use of Ex connectors, in place of hard-wired solutions, in hazardous areas.
Operators of oil and gas platforms need to continuously monitor the sites’ ambient condition status through parameters such as gas concentration levels, differential pressures and temperatures.
Mobile explosion-proof detectors and transmitters allow such measurements to be made at various key locations on the platform and then be re-positioned as required. The readings from these instruments are switched and recorded via an explosion-proof central controller. These pre-existing detectors and central controller enclosures will, typically, already have glanded conduit access points. Because of the stringent requirements of explosion-proof equipment, any modifications to such certified equipment is often avoided.
In order to save installation time and to maximise location flexibility of such a mobile detection systems onto an oil or gas platform installation, exposion-proof cable-to-cable connection solutions can be retrofitted without compromising the equipment’s Ex certification compliance.
For the links to the central controller enclosure already located on site, cables can be wired through existing glands and conduits, leaving free ends for cable-to-cable connector termination. HARTING can provide a mating cable-to-cable connector with tool-less quick-lock termination connector inserts, allowing for quick and simple non-specialist wiring on-site installation. Its Han Ex 4A cable-to-cable connector system allows the connection between the controller and the detectors to be made outside the explosion-proof enclosure, ensuring that no modifications are done to the enclosure and so there is no need for re-certification of equipment.
Connectors versus hard-wiring
Another offshore oil and gas platform related application where connectors can offer significant benefits over hard-wiring is on mobile heavy lifting cranes, which may need to be frequently removed and re-installed at different locations. While the crane platform and operator cabin will be installed in the ‘safe zone’, the boom is operating in the hazardous zone, so it is mandatory to use ATEX approved components. The boom carries a number of different sensors (for detecting angle and load, for example) and a light bar at its tip; near the cabin various connectors are used at a panel where all the sensors are wired up.
Across the general Ex sector, the replacement of defective loads, such as low-voltage switchgear, generators or pumps is complex. The power has to be switched off before the defective equipment can be uninstalled and replaced. With a hard-wired installation, all cores would have to be screwed or connected individually. Connectors, on the other hand, reduce downtime and support modern and flexible machine configuration through modularisation in hazardous areas. Connectors such as HARTING’s Han Ex series are available in different tool-less contact wiring termination designs, so that no specialist skills are needed for initial assembly and replacement of components. Similarly, the installers require no special tools, accelerating the switch-out operation while maintaining all safety functions.
Intrinsically safe explosion protection is based on the limitation of the power circulating in intrinsic circuits, permitting electrical devices to be operated safely even in an explosive environment. Han Ex connectors meet the standards for materials that are permitted to be used in potentially explosive atmospheres (DIN EN 60 079-0). Air clearance and material creepage distances are in accordance with the intrinsically safe circuit requirements for zones 1 and 2. The connectors feature a termination technique which supports unskilled assembly and flexible hood and housing mating solutions while their blue colour provides easy identification of inherently safe circuits and they ensure protection class IP65 when mated or unmated in conjunction with appropriate lanyard attachable loose covers.
Howard Forryan is a product market specialist at HARTING.>
Source: Control Engineering Europe - All Articles