Thanks speedball for your answer. That cleared it up quite a bit.

Enlight of this:

I don't really know, but I two have seen them, and I think I'll take a stab at it. Living in an older home, I have seen many of these two prong outlets get worn out to the point where they don't hold a plug in them anymore. Once it gets to this point, its time for a replacement. However, rather than install a modern grounded receptacle in its place, fooling future people into thinking the outlet is actually grounded.

So you can install it with a regular two prong outlet, although still not grounded, at least you aren't giving the false asumption that an outlet IS grounded.

However, I must confess, when these outlets get worn, I normally replace them with regular three prong outlets. I know, I know, shame on me. The three prongers are actually a bit cheaper than the older style anyway.

Actually if the construction is old enough that it has metal boxes and conduit or BX, adding a 3 prong outlet leaves a properly connected ground as long as the conduit or BX is installed properly and hasn't rusted or something. More modern practice includes a ground wire for a more positive ground. The even older knob and tube does not provide a ground or the NM from the 50's-60's without a ground wire.

Interesting, yes I will agree with that. However my house doesn't have a lick of conduit it it, any old circuits are with that old two conductor wire. And most of it is visible in the basement.

I have had a few old timers tell me that the metal box grounds through the stud. Don't know about that. Doesn't seem like a real good reliable ground to me, but I have been wrong before.

"I have had a few old timers tell me that the metal box grounds through the stud. Dont know about that. Doesnt seem like a real good reliable ground to me, but I have been wrong before."
But not this time. Metal box, wood stud, seems like that metal box's pretty well insulated to me. The problem with that statement is that older homes don't have metal studs that run back to ground. Regards, Tom

Two wire outlets are still available for the specific purpose of replacement of a broken two wire outlet, that is used on an ungrounded system. These systems are still in use in many homes. Just like the S trap, they cannot be installed in new construction, but need to be available for those still in use.

A building is only required to be built to code at the time of construction, and no one can force a building to be brought up to current code, until ANY renovation is done, then watch out.

Using three wire outlets on a two wire ungrounded system is a violation of NEC, unless a GFI is installed to protect that outlet or circuit, and only if the labels "NO EQUIPMENT GROUND" is applied to all ungrounded three wire devices.

Grounding to a metal box is only relevant if the wiring to the box has an equipment ground, such as BX cable sheathing. And then the cable needs to be confirmed that it is terminated at all points correctly to insure an equipment ground is in place thruout the entire circuit.

If the wiring is Knob & Tubing, or the two wire Romex, called Loom, then assuming the metal box is grounded is dangerous, because it is not grounded.

So Andrew, grounding is only important while you are working on appliances, and not so important at home, where your loved ones can be using the ungrounded receptacles? They put a lot of faith in you and the work done around the home. Treat yourself and your family to a huge XMAS present and get some Ground Fault devices installed before someone gets injured, or worse.

Yea, I know. My major outlets are grounded. Such as AC, refrigerator, kitchen and bath. Just my bedroom and my living rooms still have the old two prong outlets.

2 years ago, I had one outlet in the bedroom that just wouldn't hold a plug anymore, grabbed an old 3 prong I had lying around and threw it in.

This house is a work in progress, it was built good, but its had a lot of jerry riggers living it in in the 60 years it has sat here. I fix things and time and money permits, as some may know, my most recent project was replacing my cracked cast iron drain stack.

Electrically, when I moved in here, I had a nightmare. I literal "foliage" of wires coming out of the breaker box. What do I mean by foilage? Well just like a tree has its branches. You had about 5 wires coming from the breaker box, you would follow one for so long, then you would have a taped splice, then 4 wires would branch off to there sections, where you may have taped splices on any one of those.

I have a picture of one "spider web of wires" though I don't feel it nessesary to post it. One wire came from a light fixture, a taped splice led a branch to feed a 120 volt AC outlet, the other end of the splice led under the bathroom, where it was taped again, one wire led to the washing machine, the other to the bathroom rec. Then there was another splice that led to an outlet in the bedroom, and from there fed all of the light fixtures in the house.

I cleaned up all of that, but as we just moved in, and we had a sloo of other problems to attend to, (oh yea, Ive had the sewer gas problem, the no water in the shower problem, etc) some of the old two conductor wire is still there. Particularly where it travels in the walls and its difficult for me to access.

So as you can see, Im not trying to be neglagent, I just have my work cut out for me.
I have just prioritized it behind other things, as much of the old outlets use two prong electronics anyway, such as the TV, stereo, etc, however I have noticed that more and more common electronics are coming with a ground prong.

Well I guess if it was a metal stud, or wet enough, it could ground. If you are lucky the 2 conductor stuff wasn't stapled to the studs, and once loosened from the clamps in the box, could be used to pull in grounded replacements.

A few years ago, I replaced all the old 2 prong outlets in my church with 3 prong grounding through the conduit and BX. I was then largely able to banish the 2 prong adapters. It drove me up the wall to see 3 prong plugs plugged into 2 prong adapters, then plugged into a 3 prong outlet.

I think Im going to wind up drilling a new hole under the wall in the basement, then taking the old box out of the wall, fishing a new wire up, and installing a new box.

My old house was no better, in fact, it was a bit worse. I finally replaced every inch of its old two conductor wire with three conductor, 12 gauge wire.

I am going to be remodeling my attic room this spring, I have some shoddy electrical work up here I need to replace. (this is the room I told you about the "taped" drywall joints). Rebuilding a closet, etc. Once I tear into the walls of this attic, I will probobly go ahead an upgrade most of my wiring then.