In my old, mostly ungrounded house I have found a 3-prong outlet housed in a metal electrical box that behaves strangely. It operates fine, but when inspected with a digital multi-meter I observe:
- Hot to Neutral: 120V
- Hot to Ground: 80V (same for Hot to electrical box)
- Neutral to Ground: 30V (same for Neutral to electrical box)
- When I use a GFCI tester it reports "Open Ground"
- Looking at the wiring, there is a ground wire coming into the box in the romex cable but it is not connected to the outlet
- There are no outlets connected downstream from this one
My questions:
- Why am I observing these voltages to what looks like a disconnected ground?
- Is there any safety risk (e.g. electrical fire) in using this outlet as is beyond the standard ungrounded shock risks?
Best Answer
Your GFCI Tester tells it all. The ground conductor needs to be connected at the device and all the way back to the panel ground. Otherwise it is just a loose wire and the readings you are getting off of it is a "ghost" reading or a voltage reading of a very low amperage output. So it just means it is not connected properly.
The NEC Is specific about changing out a 2 prong outlet to a three prong. You must install a GFCI outlet instead, or install a GFCI device and feed the entire circuit through it, and all receptacles then must be labeled as ungrounded. If you purchase a GFCI receptacle these labels will come with it.
I did an edit on this answer to install two examples of what I am talking about which might help you understand.
Just remember your installation does not have a ground.
Stay safe and good luck.