WCA May 2016

The likely explanation for this phenomenon is the higher thermal mass provided by a thicker article thus acting as a bigger heat sink. Moreover, as the outer layer burns and creates a protective char layer, it provides a barrier for the air to reach the inner material, thus starving the system of necessary oxygen. At the same time the heat continues to get dissipated into the polymer and the conductor, further helping the cause of fire retardance. The results comparing solid vs stranded conductor also reveal a very significant impact of the construction in their relative burn behaviour. The inferior burn performance exhibited by the stranded wire is probably due to the presence of voids between insulation interior and the conductor. The presence of voids increases resistance to heat transfer between the insulation and the conductor and does not carry away heat as efficiently as that with a solid conductor. UL burn tests specify use of solid 14 AWG conductors with a 30 mil insulation thickness for VW-1 burn test under UL 44 protocol. However, material qualified for VW-1 rating is routinely used for 14 AWG stranded Cu conductor. The results clearly demonstrate that the use of stranded conductor adversely affects the burn behaviour and may lead to failure in the VW-1 test for marginal compounds. 5 References [1] “UL Standard for Safety and Thermoset-Insulated Wires and Cables, UL44,” 18 th edition, 28 th March 2014 [2] M M Hirschler “Survey of Fire Testing of Electrical Cables” Fire and Materials, 16, p107-118 (1992) [3] Elliot, P J Whiteley, R H, “A cone calorimeter test for the measurement of flammability properties of insulated wire,” Polymer Degradation and Stability, 64, p577-584 (1999) [4] “UL Standard for Safety for Wire and Cable Test Methods, UL 2556,” third edition, 22 nd March 2013 [5] J Fan and L Hunter “Engineering Apparel Fabrics and Garments,” p271, first published 2009, Woodhead Publishing Ltd and CRC Press LLC Paper courtesy of the 64 th IWCS Technical Symposium, Atlanta, Georgia, USA, November 2015.

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Wire & Cable ASIA – May/June 2016