Jim asks this question, which concerns precautions to take when using flexible cables buried in plastered walls. It has been answered by BASEC (Theme – Cable, Wiring and Wiring Accessories):
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Question: With the increasing use of flexible cables within fixed installations, what precautions should be taken?
For example, if flexible cables are 'direct buried in plaster' (although not common practice, BS7671:2008 does allow it), does the insulation dry out and become brittle, and are there other consequences that should be considered?
I guess each cable manufacturer has to provide his answer to this question...
Answer: The use of flexible cables in fixed installations is not advised - see: BS 7540-1:2005 Electric cables — Guide to use for cables with a rated voltage not exceeding 450/750 V — Part 1: General guidance, Clause 4.4.5
This states: ‘Flexible cables and cords should not be used as fixed wiring unless they are contained in an enclosure affording mechanical protection, with the following two exceptions: a) final connection to fixed equipment when the duty type of the cable is at least ordinary duty or higher; b) fixed installations in temporary buildings when the duty type of the cable is heavy duty’.
Note that flexible cables are temperature rated for use in free air and not for embedding in thermal coverings such as plaster or insulation.
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