I am doing a minor reno in a new house. I took out a wall and in it was two strands of 12-2 that went to one outlet. That wiring will not be used anymore, I don't want to splice into them or run them to a different location. I can not tell how the wires run back to the box so I can't pull them out so I want to hide then in the floor. Can I just cap it with some wire screws? Or should I put a box around it? The box is less favorable because I would have to cut a hole in the sub floor to hide it. But is that the safer option? Thanks J
Junctions and terminations must be in a box, and the box must be accessible. You can't bury it under a floor. Unless you have an idea where the source is, you'll need to treat the wires as though they're live.
There are splices rated for being closed up behind a wall without a junction box.
Once you trace the wires (I would use first a voltmeter to figure out which breaker shuts it off) then you will want to disconnect the other end, even if it is coming from another outlet.
Sometimes (when the breaker is off) I have used a toner/tracer to follow a wire.
The code is not concerned about totally disconnected wires. They are about as interesting to the NEC as the nails that hold the wood together.
Then I would cap both ends with wire nuts just to complete the job. Maybe even wrap each end (with the nuts) with electrical tape to show it is inactive.