My house is over 70 years old. Wired with armored (BX) cable - cloth wrapped hot & neutral inside. No ground wire.
I've been gradually replacing ancient receptacles with 3-prong ones. I've been pigtailing the ground screw to the metal outlet boxes. I've been testing each box with with a voltage tester (one of those little ones that's just a small light), and I've since acquired one with a digital readout for the last few. Indeed, I'm seeing the same voltage (~124v) from hot to neutral as hot to ground - indicating (i think) that the boxes, via the armored cable, are grounded.
However, I've recently read some postings claiming that armored cable doesn't provide true ground - that there is so much conductive material joined by the boxes and all of the cable sheathing that current will flow into it, but that there still may be a more direct path to ground in the event of a short circuit.
so, is that true?
I have no way to measure the current, only the voltage. Do I have a grounded system?