Q & A of the Day - What reference method when installing cable on insulation?

Question: Reference methods 100 and 101 refer to twin & earth (T/E) cable installed within various thickness of insulation. What reference method should I use when cable is installed on top of any insulation?

Answer: Regulation 523.7 of BS 7671 requires that, where a cable is to be run in a space to which thermal insulation is likely to be provided, the cable is - wherever practicable - to be fixed in a position where it will not be covered by the thermal insulation.

In the scenario described in your query, the cable would appear to be in contact with thermal insulation on one side only. Therefore, if there is free air on the remaining sides of the cable, reference method 'C' for either Table 4D2A or Table 4D5 would be appropriate.

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