if i replace 2 prong outlets with 3 prong outlets in old house (but not wiring)...

[ShawnD1]

Neutral is grounded.

Theoretically you could just tie the ground pin of the receptacle to the neutral wire (white) and say the receptacle is grounded. THIS IS NOT LEGAL, but it will work. It'll also cancel your fire insurance if you ever have an electrical fire so do not do this unless it's just some random stupid thing that doesn't have insurance anyway.

Here's my take on it:
For a random project in a building that has no insurance anyway - use the neutral wire as a ground.
For your house or some other insured building - don't fuck with it in any way. Get an electrician if you don't know what you are doing.

 

[bruceb]

A very nice dissertation of grounding facts. All seem to be right on point.

 

[nerp]

Do it right or don't do it at all.

Unless you're proud of booger work.

 

[geno]

I got lucky with our house, we have metal workboxes with BX conduit. Swapping in 3-prong outlets (making metal to metal contact between the mounting tabs and the box) worked out just fine. If you have plastic boxes or ungrounded metal boxes and only 2 wires running to the box, you might be screwed as far as getting a proper ground to the outlet.

 

[ussfletcher]

Just get some 3 prong to 2 prong adapters and go to town with them. There is really no benefit to the second ground wire (the wider slit is a ground anyway) unless you are using something that carries a risk of electrifying itself, like a toaster.

 

[lytalbayre]

also, many of the boxes you mount to, even the older ones, are metal, so you shoud be able to ground against the box itself. One thing you can do is take a testing light/plug and put one end into the hot side (the shorter one), then the other side to the screw that holds the plug in place. If it lights, then you know you are grounded. You can also buy a tester that just plugs into the socket for $5 at home depot. If it doesn't light, then i would suggest you contact a licensed electrician to correct the issue, or just use the gfci plugs as you mentioned. They will cut power at the plug if there is a short, so while not the 100%, it will still keep a shock from happening should you short something.

this

 

[Gibson486]

Correct. And if you connect the ground to the neutral at the outlet, then it's possible that a person could provide a better, or at least parallel path to ground.

NEC says otherwise,