Converting 2-prong outlets to 3-prong

Just put in a gfi with a label on it saying " ungrounded"

Thank you, I do realize that your suggestion is another alternative to my situation.

You will need to determine if your cable has the thin bond wire that allows the cable to be used as a grounding means. Look near your panel at the cables.

Putting a ground to the back of the box would serve no purpose its either ghe gfi or a rewire which is something to consider in the future

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MJJK said:

I have read several posts, on this web site about changing 2-prong receptacles to 3-prong receptacles. I am still confused if I can safely do the following: My daughter's recently purchased 1952 home with BX cable (2 conductor) wired (with steel boxes) has all 2-prong receptacles, except in the kitchen where there are GFCIs. With each 2-prong outlet, if I first determine that I have a proper ground between the hot conductor and steel box (by using a 100w incandescent bulb as my tester). Then next, if I affix a ground wire pigtail to the back of the steel box and to the new 3-prong receptacle ground screw, will this serve as a proper and safe grounded 3-prong receptacle?

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This will only work if the steel box (j box) is properly earthed.
I am not sure what code says,
as it varies from area to area.

About 25 years ago I was faced with a similar problem and basically I handled it as the OP did. I definitely had that thin uninsulated third wire that ran along side the hot and common. Having checked the outlet with a meter (hot and ground) I was convinced the outlet was grounded. I am not suggesting that this meets present code and if it does not of course I would like to know that as well. I reasoned that the service panel was grounded and that the metal cable carried the ground to the outlet box. In my visits to the big box store I later found that there are outlets that ground w/o a ground wire to the green screw but they cost a bit more and must only be used with a grounded metal box.

The thin bonding strip is the key. If you have it, the armoured cable can be used as the ground. A jumper from the box to the outlet can be added.

If the bonding strip does not exist, it cannot be used. Even if you get the test light to light showing that some "ground" exists, it is unsafe/against code to use it.