GFCI Testing – GFCI Without Equipment Ground Fails Testing

Any equipment that uses a two prong plug will be as safe being plugged into this setup as they would be if they were plugged into a properly grounded three prong outlet. Two prong plugs (obviously) do not use the ground pin. As for three prong plugs, this depends on what is being plugged in. If the item is a laptop power supply that is sealed in a plastic shell, the ground pin is pretty much ISO-proforma [meaning, that is the standard cord- whether the equipment needs a ground or not.] I would be hesitant to plug in something with a metal shell, like a full size desk top tower, because the power supply is enclosed in a metal shell and attached directly to the frame of the case, this could present a shock hazard if the power supply were to malfunction.

A GFCI is a good start. If they are functioning properly, they will guard against lethal shocks, but you may still get a tingle if the electric is not quite right.

A possible suggestion: Use a 2->3 pin converter and attach a ground wire to the grounding tab. Attach the other end of the wire to a radiator if you have steam heat or possibly a metal water pipe. (no gas pipes.) This will get you a ground and you can use those items safely.

The cheapie 3-light testers work by connecting 3 lamps in a triangle fashion across the 3 outlet pins. The hot-neutral lamp works in the obvious way. The hot-ground lamp works if the ground pin can find a path back to neutral, presumably via a ground wire correctly bonded to neutral in the panel. But not necessarily.

It sounds like the UPS is connecting neutral to ground in some way. Perhaps with its own onboard ground tester.

All of this is idle amusement. If you know there's no ground wire, then that's your answer - the tester's output is irrelevant. These testers are a little bit hokey and are not the last word on the subject.