Does your house have metal conduit to each box or is it a two conductor cable? If it is conduit and metal boxes then you can probably just ground the receptacles to the boxes. If it is a two conductor cable then you will have to run a ground wire to each box and back to the main panel. It will terminate on the grounding strip in the panel if there is one or to the neutral bus if there is no ground strip. This can be done by anyone if they are very careful and turn off the power. I do suggest reading up on how to go about it if you can find a good resource material. Also check the national electric code to be sure you follow all codes. It is permissable to replace two prong receptacles with gfci recepticles if you properly label them with a sign that says no equipment ground. This still does not supply a ground but makes them a little safer. Grounds provide a alternate path for current to help initiate an overcurrent device. They also bleed of static electricity which can affect hi-tech equipment like computers.

I used to install and service computers and we would NEVER say that metal conduit is an acceptable ground for sensitive electronic equipment. The connections are too poor for that, especially in older buildings. I have seen many computer problems cleared up by running an isolated ground to a cold water pipe.
Here's a URL for helpful wiring info. http://www.danswiringpage.com/

[This message has been edited by rpxlpx (edited February 09, 2001).]

Metal conduit is a legal ground if it is continuous to the panel box with no breaks. It will meet code requirements for the national electric code. It may not meet local codes in some places. Is it the best way to ground? Absolutely NOT. But if you are looking for the easiest way to ground an existing house that has metal conduit then this is the easiest way. It is always best when running an outlet for a computer to run an isolated ground. This means in addition to the regular ground wire another ground wire must be installed and ran all the way back to the grounding electrode system. The problem with using cold water pipe only is it may have been patched somewhere with pvc pipe making it noncontinous to ground. Also if you do use a cold water pipe there are code restrictions on where you can attach to such as within 5 feet of the point of entree into the house. All cold water grounds must be supplemented with another system usually a driven ground rod.

Please refer to my post under "my outlets are upside down ;(" for a discussion of alternatives to running new ground wire. In short, you can replace your outlets with GFCI outlets, which would be slightly expensive ($7-$15 an outlet), but less expensive than re-wiring or hiring a pro to re-wire.

Wiring a ground wire is virtually the same as re-wiring the entire house: it is a big deal, especially through finished walls. You can do it, but you will need to figure out the electrical plan and how wires run through the house to service that plan. As Electric Bill wrote, please read up on doing it if you plan to do it yourself. Buy one of the Electrical Wiring Books. Homne Depot just came out with one, and Black and Decker publishes one that I use that is great.

Metal conduit is fine for a grounda, although not perfect. It is less preferable to a seperate ground wire because it is exposed, which could shock you if a short circuit occurs. The current returns through the ground in a short circuit, so the metal conduit will be hot with electreicity in the event of a short circuit. Even if buried inside a wall, it couyld contact some metal part that is exposed, and that metal part would then become electrified. Not so with ground wires that are covered by sheathing.

The other problem with using conduit as a ground is that there is a greater chance that the ground will be interrupted if, say, someone later removes the conduit somewhere along the circuit and replaces it with NM cable, not knowing that the conduit served as the ground. Then the ground will be incomplete, and the same as if there was no ground.

As a result, if you have metal boxes and metal conduit or armored cable, test the metal conduit for continuity before relying upon it as a ground. Touch a circuit tester on the hot wire and the metal box. If it lights up, then it can serve as a ground. If not, there is an interruption somewhere along the circuit, and it will not work.

[This message has been edited by Lawrence (edited February 15, 2001).]