Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, concerning a domestic wiring situation and what reference method to use, is answered by SELECT:
A flat twin & earth cable clipped to floor joists under a floor within a house, where the building void is less than 50 x diameter of the cable for approximately 20m (Reference Method B), then run within a thermally insulated wall for approximately 500mm (Method 100) to a final connection.
I would assume that the correct reference method would be Method 100 as this would have the most impact on the cable's current carrying capacity because of the thermal insulation. However, I'm not sure whether it should be the longest part of the run which would be Method B.
Please advise…?
Answer: You should always take the worst-case scenario, which, in your case, is within a thermally insulated wall. If it is a stud wall with thermal insulation, it will be either Method 102 or 103 (see Table 4A2 on page 265 of the Regulations).
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