WCA May 2016

❍ ❍ Figure 3 : Effect of conductor type on burn duration for different formulations for 30 mil insulation thickness The data also suggests that VB-1 is better than VB-2 in flame-retardance as evidenced by the higher uncharred length and shorter burn duration. no burn time recorded for the 60 mil insulation with VB-1 formulation. These results are in line with the expectation that for insulation or articles made with flame-retardant materials, it is increasingly difficult to start a sustainable fire. The data also shows that for the less flame-retardant material, ie, for HB-1 sample in this case, the opposite may be true. This observation can be easily explained by the fact that below a minimum level of flame-retardance when thicker materials do catch and support a sustaining flame, they will just burn longer because of the larger mass of available flammable material. For both cases with HB-1 formulation, the wire samples burn all the way through the flag leaving no uncharred length. The effect of insulation thickness on the burn behaviour can also be expressed by the uncharred length of the samples as shown in Figure 2 . The results are shown only for the VW-1 rated samples as the horizontal burn rated sample burns through the entire length of the wire leaving no uncharred length. It is seen that for both the formulations, the uncharred length is higher for the thicker sample, indicating a greater flame-retardance with increase in thickness.

30 mil 60 mil

Uncharred length (mm)

24" wire specimens affixed with Kraft paper strips at their tops were suspended vertically in a draft-free chamber. A 37 ±1 MJ/m 3 methane flame was impinged upon the samples at an angle of 20° to the vertical. The impingement point of the flame was 254 ±2mm below the bottom of the Kraft paper strip. A continuous layer of surgical cotton was placed below the specimens such that the surface of the cotton was 235 ±6mm below the impingement point of the flame. Each specimen was subjugated to five 15-second appli- cations of flame. The interval between flame applications was 15 seconds and the interval was maintained for all applications where the specimen self-extinguished prior to the elapse of the 15 seconds. For samples burning longer than 15 seconds but shorter than 60 seconds, the next application of flame was done when the sample self extinguished. In order for a sample to have passed the VW-1 burn test, all of the following criteria must have been met: • Less than 25 per cent of the Kraft paper indicator was burned • The specimen did not burn longer than 60 seconds after any of the five applications of flame • The cotton batting was not ignited by either flaming or glowing particles or flaming drops In addition to these criteria, the burn performances of the specimens in this study were characterised by the following parameters: • Uncharred length – the distance below the Kraft paper indicator that is not burned and maintained a smooth, unblemished surface after wiping with a soft cloth • Average burn time – the duration that the specimen continued to burn after the removal of the flame and averaged over the five flame applications. For burn durations greater than 60 seconds, the time was measured until the Kraft paper began to burn ❍ ❍ Figure 2 : Effect of insulation thickness on uncharred length in VW-1 type test for different FR formulations (solid conductors)

Solid Stranded

Burn duration (sec)

❍ ❍ Figure 4 : Effect of conductor type on burn duration for different formulations for 60 mil insulation thickness

Solid Stranded

3 Results and Discussion 3.1 Effect of insulation thickness

The effect of insulation thickness on the performance of multiple compositions in a VW-1 type test is shown in Figure 1 for 14 AWG solid Cu conductors. The results show that for the two higher flame-retardant compositions, the burn duration decreases as insulation thickness increases with

Burn duration (sec)

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Wire & Cable ASIA – May/June 2016