Posted By Ken Taylor The IEE Regs require that wiring systems are erected so that no damage is caused by the ingress of water during use and maintenance. Beyond that (other than specific requirements for bathrooms, swimming pools, etc) I believe it to be a matter for the professional judgement of the competent installer and tester. The risk points will generally be at socket outlets, junction boxes and other points of connection rather than through intact insulation and armouring. It is very common to see water and electricity services in proximity in both ducts and surface mounted. Compression joints adjacent to switchgear, fuse-boards and the like are the sort of situations to look out for.