Electrical Wiring in the Home/Ground wires
I have found several outlets in my home that do not have a ground. Can this be fixed by running just a bare copper ground wire to the outlet OR does the entire cable have to be replaced (hot, neutral plus ground)?
Unfortunately, you are not going to get an easy answer to this question. Some people believe it is OK, some do not. It really isn't covered in the code, since the code applies to new construction. I personally believe in doing it right (new cable), if you can.
You are also allowed to use grounded outlets without the ground wire if you use a GFCI on the circuit and put a sticker on the outlet saying "no equipment ground."
About Electrical Wiring in the Home
This site answers questions related to home electrical wiring, home wiring, general electrical help,and other electrical questions related to aleternating current (AC). You can find help on the National Electical Code, home electrical issues, wiring electrical outlets, installing lighting, electrical grounding, and general electrical help for do-it-yourself projects not require an electrician. If you do not see your home electrical wiring question answered in this area then please ask your electrical wiring question here