EuroWire November 2017

Technical article

Development and Qualification of a High Performance Zero Halogen Primary 90°CWet Rated LV

Insulation System By Mike E Slevin, David G Roberts, Allan P Marconi and James Freestone, SACO AEI Polymers

Abstract This paper describes the development and qualification of a moisture curable low smoke zero halogen (LSZH) cable insulation meeting UL 44 requirements. The overall development concept is outlined and data is presented on the final compound formulation showing that fire, electrical, mechanical and physical requirements have been comfortably exceeded. Industrial scale extrusion performance is also briefly reviewed. As LSZH cable types are deployed more widely in North America, this development should provide a solid platform for both new cable designs and future compound development. 1 Introduction There is growing interest at the global level in providing low smoke zero halogen (LSZH) solutions for all cable styles; this is particularly relevant in the built infrastructure with high human occupancy including mass transit, commercial buildings, airports and similar public places and [1, 2] . The use of LSZH insulations (to 1,000V) is now well established in many international markets and supported by international and national standards. The initial considerations for a material to work as an insulation in a low

of a complete cable in full-scale vertical (ladder) flame tests. Higher performance than that evidenced by an FT2 test is often desired in insulated singles. The purpose of this work was to furnish an LSZH system meeting UL 44 XHHW-2 requirements along with the optional fluid resistance requirements with the process advantages of a moisture cure solution. Initial product development focused on two challenges. First was identifying the flame retardant filler system to provide stable insulation resistance at 90ºC in water. Second was meeting the horizontal flame performance requirements of UL 44 with additional smoke and flame characteristics to offer a good balance of properties in a full-scale fire test. process approaches including CV, e-beam and moisture cure were investigated. Through a combination of a high-purity filler and moisture-repellant additive chemistry together with careful optimisation of the polymer system and graft chemistry, an excellent balance of properties has been achieved. 2 Development The key initial targets were to meet, as a minimum, the UL FT2 horizontal fire test requirements on 14 AWG copper as detailed in UL2556 and to meet the long-term insulation requirements for 90°C wet rated XHHW-2 as detailed in Careful consideration of

voltage (LV) system are the abilities to handle installation temperature (cold properties), to withstand the mechanical rigours of installation and finally to offer good mechanical and thermal ageing characteristics during service. Additionally, the insulation in a single conductor wire and cable defines the complete installed product and may need to offer good fluid (oil) resistance, which is an important challenge in developing a robust LSZH insulation. LV insulations place an additional demand on LV insulation systems with requirements for long-term wet electrical stability. Cross-linked insulations offer important benefits in providing the highest level of protection in overload conditions and are often preferred against thermoplastic styles. Practical manufacturing approaches for cross-linking LSZH insulation systems include organic peroxide (CV) or electron beam systems entailing significant capital expense. A moisture cure approach offers important manufacturing efficiencies, avoids the high capital expenditure and affords significant manufacturing flexibility. The minimum fire performance for an insulation built to UL 44 is the FT2 horizontal burn; single insulated cores can be a stand-alone product or are further built into multi-conductor cables. Hence the insulation must also be able to function on its own or as a component North American standards for

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November 2017