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Aircraft carriers rely on composite junction boxes

Aircraft carriers rely on composite junction boxes Challenging applications often benefit from thinking outside the box. This was just the case when junction boxes were being sourced for the lighting systems onboard the Royal Navy's new aircraft carriers.

BVT Surface Fleet Solutions is currently undergoing the process of building two of the world's largest aircraft carriers for the Royal Navy; the HMS Queen Elizabeth, due to be completed in 2016, and the HMS Prince of Wales, due to be completed in 2018. Rather than using traditional metal junction boxes, which are prone to corrosion damage and denting, the ship builder has opted to specify polycarbonate enclosures.

Aircraft carriers are a vital component of modern naval strategy. The massive vessels act as mobile landing strips for aircraft, allowing them to access parts of the world that they wouldn't usually have the range to reach. The current project to build two new aircraft carriers is one of the most significant naval investments made by the Ministry of Defence since the turn of the century. The HMS Queen Elizabeth, which will be the first of the QE class carriers to be finished, is currently in its second stage of production.

The two carriers will each require 40,000 tonnes of steel and will weigh approximately 65,000 tonnes. Their power stations will generate 110MW and over 1.5 million metres of cable will be used across each carrier. Once at sea the ship's engineers will have extremely limited access to spare parts; so it's important that all the components specified are capable of surviving in the harsh maritime environment and performing their roles reliably.

In order to provide adequate protection to electrical connections, the junction boxes which are used on such a project need to be extremely tough. Being a maritime application it is important that the junction boxes provide suitable ingress protection while also offering corrosion resistance from the abrasive salt particles present in the water and the air. It is likely that the components will also be subjected to constant vibration which can often result in screws coming loose, meaning that the lids must be secured using a alternative method. To meet the challenging applications, the shipbuilder selected Abox polycarbonate enclosures from Spelsberg. polycarbonate, IP65 Abox enclosure for the project. By supplying the enclosures assembled (including terminals) Spelsberg was able to help the ship builder greatly reduce on-site installation time.

Design considerations
Chris Lloyd, General Manager for Spelsberg UK, comments: "Because this is a military spec project it might be expected that only metal junction boxes would be considered for the application. However, when we first spoke to the ship builders it quickly became clear that a tough, polycarbonate solution would actually be more suitable. Not only are metal enclosures more likely to corrode in the salty environment, they are also prone to denting during collisions; and with heavy military equipment passing through narrow corridors collisions are almost guaranteed."

Another consideration, and one that may seem strange considering the application, is weight saving. While it might seem odd to worry about the weight of a junction box on a 65,000 tonne aircraft carrier, the ship builders are very much aware that combined weight savings over all the onboard components across the entire span of the ship can result in very real performance improvements. Reduced weight will also result in lower delivery costs and improved installation times, which contributes to meeting the delivery schedule and budget of the project.

The Abox range is made from halogen-free materials and is available with a vast array of specifications in terms of size, IP rating, gland type and terminal type. From the Abox 025, measuring just 80mm x 80mm right up to the Abox 2400 with dimensions of 640mm x 320mm, there is a product to suit most applications.  A red cover can also be specified to identify circuits for safety lighting.

The industrial quality (IQ) versions of these junction boxes have an IK08 rating for protection against mechanical stress and the range is available with a variety of accessories which allow termination of cables with cross sections from 1.5mm2 up to 240mm2.  The SL series of Abox, equipped with the screwless terminals, are approved for use on ships and in offshore applications by Lloyds Register.  This approval was crucial in the specifications offered to the client.

The range is built with at least 8 potential cable entry points and has a number of accessories which can specified, including various terminals, cable clamps, glands, mounting rails and plates as well as sealing kits. For applications where the enclosure may be fully submerged a cast resin sealing kit is available which provides IP68 protection up to 15 metres.
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