Published: 7 April 2015
Category: Q&A
John asks this question, concerning the calculation of the size of conductors and rating factors. It has been answered by SELECT (Theme – Cables, Wiring and Wiring Accessories):
This Q & A is one of thousands posted in our Technical Expertise area, and answered on a daily basis by our Voltimum Experts.
Question: When calculating the size of conductors, a debate has arisen regarding the application of rating factors - can you please help?
When more than one condition for the application of factors exists, then we must consider the worst case. If, as an example, a cable runs through an area of high ambient temperature, and if it is grouped with several other cables at another location and is finally run totally enclosed in thermal insulation at another point, then we consider all the factors and apply the most onerous.
However, if more than one condition applies at a single location then we must apply all those factors.
Some people in our office insist that all of the factors have to be applied at all times, even if they only affect the cable at differing stages along the run. However, the other people insist that the factors are only all applied if it takes place at one point in the entire run.
At all times they have to be considered, BUT, what about applying them?
Answer: Application factors for ambient temperature, grouping and when cables are completely surrounded by thermal insulation need to be identified. These factors should be applied individually.
All factors would only be applied if ALL conditions were effective simultaneously.
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