I need to ground outlets in my house and need to pigtail the ground wires. Just wondering if I can salvage the old neutral wires, strip them, and use them to pigtail to the outlet instead of cutting off extra ground wire.
Yes, as long as they are thick enough (thicker is always OK) and you must strip the whole wire because grounds must be green or bare, not white or any other color. If you are concerned about the ground wires shorting against screws, put tape over the screws, not over the ground wires.
For 15A - 30A, the sizes are the same as the hot & neutral for the same size circuits:
- 15A - 14 AWG
- 20A - 12 AWG
- 30A - 10 AWG
Above 30A, you get to downsize:
- 40A - 10 AWG
- 50A - 10 AWG
- 60A - 10 AWG
- 100A - 8 AWG
- 200A - 6 AWG
Yes, that's fine.
The ground wire needs to be thick enough for requirements. For instance if you are wiring up a #6 range circuit, the ground is #10. If your piece of scrap is #8, that is fine. A #12 would not do.
The ground wire must be yellow/green, green, or bare. You cannot recolor wires unless they are #4 or larger*, but if you strip it bare, I won't tell :) Just make sure this type of wire lends itself to being stripped bare; for instance the stranded THHN I use would quickly tangle into a rat's nest.
EXCEPT: You are always allowed to re-mark a wire within the category it's already in.
- Hot: Black brown red orange yellow pink blue purple
- Neutral: white gray
- Ground: yellow/green green bare
So you can re-mark a bare wire green. If you have a white wire you want as a ground pigtail, and you don't want a bare wire, then you strip the white wire bare, then you tape-wrap the bare wire with green tape (legal).
* Except in cables, you can remark white to be a hot.