I recently bought an older home. Started remodeling the bathroom on the top floor and realized after opening some walls, that the entire top floor is old knob & tube electrical. I figured my best course of action would be to run a subpanel up to the top floor and rewire the entire top floor from the attic. My question is do I go with a 70amp sub or a 100amp. And what wire do I use? No.6 for 70amp and No.4 for 100amp? Any help would be appreciated. Thanks!

No on the wire size, just wait for TK to answer your question. In the mean time tell us how the knob and tube wire is eventually getting power from the panel below, why not just replace the wiring from the existing panel up to the top floor. You may need a permit if this is extensive.

Appears that the previous owners in order to sell the house,ran good wires from the panel box enough to almost hide the knob and tube. Its 100amp panel in the basement, basically what they did was run romex and/or BX right up to the ceiling in the basement, put in a junction box and tied in the knob and tube there. So at first appearance the main panel looks good, until you actually follow the wiring all the way. I'm even finding buried junction boxes behind walls. Its really upsetting. I feel like I'm on a eposide of Holmes Inspections on HGTV.

I'm figuring it would be easier/more cost effective to have a sub panel up on the top floor instead of running a whole bunch of wires down two flights to the basement's main panel. So what I figured to do was run new wires from the panel in the basement and up through the basement floor for the main level. And for the top "third floor" id have a sub panel up there and feed down from the attic.

Hope I'm explaining myself correctly here. Just frustrated and looking for ideas. One simple retile job in a bathroom has become a rewiring of the entire house. Serves me right for trying to restore a 100 year old house.

Again TK will give you the best option but I believe a covered junction box is acceptable but not inside the wall. You may have just cut your task by 75%. Thanks Don, I made the correction so as to not mislead anyone who did not see your post after mine. TX

Sorry, but all junction boxes have to be accessible.

You need to have access to the contents of the box without removing or damaging any walls or ceilings.

How many circuits are needed on the second floor? Just one bathroom and some bedrooms?

Anything else, such as air conditioners?

I need some detail of what loads there are on the second floor.

TK, There will be a pretty large bathroom with a double sink vanity & a makeup counter, four bedrooms, at least one will have to have an window AC unit. Another bedroom will be an office with computers, copier, fax etc.

I would install a #2 aluminum 4 wire SER cable to a subpanel on the second floor. Perhaps a 12-16 circuit panel should be sufficient, and protect it with a 60 amp breaker.

I will assume you already know about Arc Fault protection of all branch circuits but the bathroom, GFI receptacle in bathroom, smoke detectors in each bedroom and one in the common area, all interconnected with the smoke detectors on the other levels of the home.

You should check with your local building official about these bedrooms, they may need second egress in the event of fire. While your at the building inspectors office, you can check into permit for the electrical work.