I have a question about the wiring in my apartment which may not be up to code (New York City building, built circa 1910). While a contractor was attempting to install a ceiling fan, I was asked to cut the power to the area of the ceiling fixture by unscrewing the fuse feeding power to it. After I did so, the contractor allowed two of several wires in the area around the fixture to touch and caused a spark--not a large one indicating a short, but a noticeable one nonetheless. I had to unscrew the fuse powering an adjacent area of the apt to keep the spark from re-occurring. I was told that the two fuse lines seemed to share a neutral. My questions are: (a) does the above description mean that a neutral wire is actually being shared by two branch circuits each with their own fuses; and (if yes) (b) is this permissible under the current code; and (if not) (c) which sections of the code would be applicable to this situation?
Thank you very much.