A few months ago, we purchased a 3 bedroom, 2 bath 1800 sq. ft.home built in the mid-1960's. We've started to try to update the rooms (stripping wallpaper, painting - nothing major), and this weekend, decided to do the master bathroom. These bathrooms are tiny - maybe 6x5 feet - with tile covering most of the wall like wainscotting. Above the sink was a mirror that we discovered was hiding an in-set medicine cabinet, and a hole where an old wall sconce used to be located. Above the toilet was a new wall sconce, and when I removed it to strip the wallpaper, discovered that there was no junction box, and that it had an extension wire spliced to the old junction box. After much reading, I'm discovering several problems, and want to know if the way I think I can fix it will be an approved repair.
First, the extension wire that was spliced from the original junction box to their light fixture didn't have a ground wire, and the ground wire is just "hanging out" in the junction box. Then, of course, they didn't have a junction box, and the extension wire is 16 gauge (I forgot to look at the circuit breaker to see what amp the circuit is, but I'm betting it is 20). We thought we'd take this opportunity to put a new 3-light sconce up above our medicine cabinet, but of course, we can't use the old junction box because it's hidden behind the medicine cabinet, and the original romex cable coming into the junction box is not long enough to move to a new junction box.
Assuming the circuit is 20 amp, could I get new cable and splice the white/white, black/black, and ground/ground inside the old junction box, and then run the cable the 8 inches up the wall into a new "old work" blue plastic junction box for a light fixture? I'd get a cover for the old junction box, and our medicine cabinet would conceal it so it would still be accessible as per code, but not viewable every day. I'd then follow the lighting fixture guidlines for coupling the white/ white and black/black, but how would I handle the ground? The instructions are to put the fixture's ground wire to the screw, but then what would I do with the ground from the extension cable?
Thanks if you made it through this long question.