Members working with insulation in floor voids, in accordance with Part L of the ÐÇ¿Õ´«Ã½ Regulations, should derate installation cables by a factor of 0.55 if the cables are entirely surrounded by insulation, advises the ECA. In practice, this would mean installing a 4mm2 twin and earth cable with a 32 A ring circuit. Alternatives include fitting a 20 A protective device, creating a 75 mm void around the cable or using radial circuits.

Source

Electrical and Mechanical Contractor