Two different cases that need to be considered are: So that cables installed in such locations will remain sufficient to meet the requirements of BS 7671, the cross-sectional area of conductors may need to be increased to compensate for any reduction in the current-carrying capacity due to thermal insulation. Consequently, as shown in Fig 1, contact with thermal insulation is generally unavoidable for most twin and earth cables installed in domestic and similar premises. However, it is common practice for thermally insulating materials to be installed in the walls and ceilings of domestic and similar premises to satisfy the energy efficiency and noise requirements of Building Regulations. Otherwise, the operating temperature of the conductors may be exceeded (70˚C for thermoplastic (pvc) insulated conductors), possibly leading to a reduction in the service life of the cable or damage to the insulation of the conductors or adjacent material (Regulation 523.9 of BS 7671 refers). Whilst the current-carrying capacity of a cable is dependent on a number of factors, this article looks at the impact of thermally insulating materials on the current-carrying capacity of flat twin and earth cables installed in domestic premises.Ī cable that is run in a space where thermal insulation is likely to be applied, such as in the loft of a dwelling, should preferably be installed so that contact with the thermal insulation is avoided.
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