A little DIY job.

One of the diy jobs that I find really easy to do others struggle to comprehend, that job is changing a ceiling rose for a light. When undone and people see red and black cables, these are the old colour cables by the way, they assume that all black cables and all red cables go together, big mistake. The resultant big bang when they put the power back on shows this is not the case, what they fail to realise that maybe one of those black cables is not really a black cable, it is a red cable. To make this a bit clearer when the cables were being installed originally one of the pairs of cables used were taken to the switch and as such is a switch wire, the black used should have had a red sleeve put over it to signify that it was a switch wire and is live, and not a neutral as the other blacks usually are. Obviously if the installation was done correctly the cable taken to the switch should have been a twin red (again these are old colours).