Different Types of Cables - Research Proposal Example

Introduction and Objectives In any building there is likely to be different types of cables each representing a potential hidden danger that is capable of providing a full fire load with potential of spreading rapidly in the building (Chase, 2001). This makes it important for cables to be tested so as to approve them to the appropriate standards. Fire retardant cables are designed for application in fire situations where there is need to retard the spread of flames along the cable route (Montogomery, 2001). There is a wide application of fire retardant cables owing to their low cost (Anglogold, 2002). The cables may be installed in single wires or in bundles but there will be flame retardation confining the flame to a small and this reduces the fire hazard that could be due to propagation. The purpose of this experiment was to test flame propagation characteristics of a single wire or cable. In the test a 440mm cable sample was fixed vertically and a 125mm long flame was applied at 45 degrees from a gas burner which was placed at the bottom of the cable. In the experiment the specimen is said to have passed the test if after burning has stopped, the charred or the affected position has not reached the lower edge of the top clamp which was equivalent to 420mm above the point of flame application. Procedure A one metre cable was placed into the top and bottom clamps to make it tight and a 20mm line was marked out from the top edge of the bottom clamp so that a burning distance of 420mm was left. The Bunsen burner flame height was then set to approximately 125mm with an inner blue cone. A filter paper was placed underneath the cable and it was ensured that the thermocouples were touching the top and the bottom of the wire at the same time the data being on. The flame was impinged on the 20mm line mark at 45 degrees angle with the flame being left in this position for 60 seconds before being removed. The temperature from the thermocouples were recorded every 15 second while observation of the cable if it could burn to the top clamp or if droplets emanating from cable could ignite the filter paper. This procedure was repeated for second sample of a different cable. For the remaining two samples the clamps were set up at an angle or a slope of approximately 45 degrees with the widest part being at the bottom. Results Sample – Green and yellow striped Nylon (7 core) - Vertical 440mm test length - Length of sample burnt – 440mm. Time of test – 7minutes Sample failed Table 1 Time (seconds) Top thermocouple (°C) Bottom thermocouple (°C) 0 21.5 21.5 15 25.5 33.5 30 32 75 45 35 121 60 35.5 140 75 36 168 90 36 183 105 37 205 120 39 213 135 42 227 150 47 244 165 51 257 180 60 271 195 71 243 210 85 219 225 98 209 240 101 188 255 119 161 270 127 149 285 135 122 300 142 88 315 151 69 330 169 56 345 175 49.5 360 183 44 375 205 39.5 390 219 38 405 231 35.5 420 245 33.5 Figure 1 From table 1 it can be seen that it can be seen that there was a steady increase in temperature registered at the bottom thermocouple. The temperature increased from 21.5 oC at time 0 seconds to 271 oC 180 seconds. After the 180 seconds the flame was removed and this caused the drop in temperature to be registered. From figure 1 it can be seen that there was a rapid drop in temperature registered by the bottom thermocouple up to the point when the temperature reached the 50 oC. The test experiment failed as the entire cable length of 440 mm was burnt when a flame was introduced at the bottom thermocouple. The cable allowed faster and complete frame propagation from its point of application as indicated by corresponding increase in temperatures at the top thermocouple. This therefore shows that the cable may expose a building to full load flame propagation, hence becoming a fire hazard and it should not be approved for use as a standard fire retardant cable. Sample – Green and yellow striped Nylon (7 core) – 45 degree angle 440mm test length - Length of sample burnt – 170mm. Time of test – 2 minutes 40 seconds Sample – Passed Table 2 Time (seconds) Top thermocouple (°C) Bottom thermocouple (°C) 0 25 26 15 27 111 30 27 158 45 27 201 60 31 245 75 31 289 90 31 307 105 32 328 120 32 358.5 135 32 240 150 33 168.5 165 33 135.5 180 31 113 195 31 113 210 31 94 225 31 77 240 31 69 Figure 2 From the graph above we can see that within the first 120 seconds the top thermocouple reaches maximum temperatures, but relatively there is no change in temperature at the top thermocouple. The cable passes the test on this angled orientation as at about 2 minutes and 40 seconds only a length of 170 mm of the cable had burnt. Since this was the same cable that failed the test in its vertical orientation on first experiment, then we can say that depending on the cable orientation angle to the flame source, a particular cable can change its property in flame propagation. Therefore vertical orientation expose a cable to fully potential flame propagation and this can be hazard in buildings. Cable - Flame propagation results Sample – White PVC (3 core) - Vertical 440mm test length - Length of sample burnt – 200mm. Time of test – 1.26 minutes Sample Passed Table 3 Time (seconds) Top thermocouple (°C) Bottom thermocouple (°C) 0 25 25 15 201 25 30 377 25 45 410 24.5 60 840 25 75 208 27 90 108 26 Figure 3 From the above graph you can get that the cable passed the test as at 1.26 minutes a length of 200 mm of the cable had burnt. The bottom thermocouple temperatures at the 60th minutes reaches a maximum temperatures but there is relatively no increase in temperature of the top thermocouple as there no heat transfer along the sample cable. This shows that this cable can be used as a fire retardant cable as there is no full flame propagation along the vertical cable. This cable can not allow fire propagation through wire cables routes in the buildings, as they will not allow flames to be transferred through the entire sample cable and this will puts off the flames. Cable - Flame propagation results Sample – White PVC (3 core) – 45 degree angle 440mm test length - Length of sample burnt – 220mm. Time of test – 1.24 minutes Sample Passed Table 4 Time (seconds) Bottom thermocouple (°C) Top thermocouple (°C) 0 25.5 27 15 37.5 25.5 30 54.5 25 45 64.5 25 60 70.5 25 75 70 25 90 69 25 Figure 4 From this last experiment we can get that the sample cable passed the test, as at 1.24 minutes a length of 220 mm of the sample cable had burnt. The bottom thermocouple displayed a temperature increase where as the top thermocouple showed a relatively no change in temperature. This shows that despite the 45 degree angle orientation, the cable still prevented flame propagation throughout the entire cable. Therefore the cable can be used as fire retardant in buildings to avoid spread of fire through wire cable channels. Discussion It is clear that in some circumstances a cable can fail a flame propagation test depending on the angle of the cable. The flame may fail the test in the vertical position while the cable may pass the test when at a 45 degree angle. This is clearly seen from the Green and yellow striped Nylon cable which failed the propagation test in the vertical position but past the test at 45 degrees orientation. The angle of the cable determines the amount of heat the cable is exposed to with the vertical orientation having the maximum heat exposure. When the heat exposure is high it will result in a high propagation of the flame which may lead to the failure of the cable. High propagation will result in high temperature top thermocouple. On the other hand for a case where the cable has poor flame propagation the temperature will increase highly at the bottom of thermocouple while at the top thermocouple the temperature will remain relatively constant. The increase in the temperature at the bottom thermocouple will be dependant on the angle of the cable. Conclusion From the test the following conclusion can be made. Cables are likely to fail a flame propagation test when vertical that when they are at an angle. There will be very high temperature at the bottom thermocouples for cables with poor flame propagation with the highest temperature being recorded for the cables with vertical orientation. References Anglogold (2002). Elelectric cables with extruded solid dielectric for fixed installation. 565/1 Chase, D. et al. (2001). “UV Cure Fiber Optic Buffering Resins,” Proceedings of the Fiftieth IWCS/FOCUS, 529-531. Montogomery E. (2001).UV-Curable Buffer Resins vs. Thermoplastics: A Closer Look at New Flame Retardant, UV-Curable Materials in Tight Buffered Cables Read More