One thing that doesn't seem to have been mentioned yet is the insurance aspect of faulty wiring. When I set up my garage for my layout I got a professional in so I could get the wiring *(of the garage) certified when I could easily have got my father in law to do it far more cheaply. The reason being that I work in insurance industry reviewing complaints and every day on my desk I see loads of knocked back claims because people didn't go to the trouble of getting a professional to do the job. The reason Warley will be checking layouts is because their insurance may well be conditional upon that. If you do not have a valid certificate for your wiring you may well find any claim for an incident such as this would be rejected due to exclusions for faulty workmanship or the like.