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The paper "Different Types of Cables" is a perfect example of a research proposal on engineering and construction. In any building, there are likely to be different types of cables each representing a potential hidden danger that is capable of providing a full fire load with the potential of spreading rapidly in the building (Chase, 2001)…
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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
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