Hi. I have a few three-prong outlets in the home we just bought that are not grounded when I test them. Most of the outlets on the circuit are two-prong. So, I'm not sure if these three prong outlets were properly installed. When I open up the receptacle I see the grounding wire and it has been screwed into the receptacle. Why isn't it grounded then?
Hello thebigad. Welcome to the Community!
Testing these outlets is a great idea. What you have found is that whoever installed the 3 prong outlets just assumed that using a short ground wire from the outlet to the metal outlet box would ground the system. Your tester showed that that is not the case. Testers like these can be a quick and handy way to ensure proper wiring. They come in a standard version as well as one with a GFCI test function as well:
An electrical system which uses metal conduit tubing often uses that metal to provide the system ground. This eliminates the need for separate green or bare ground wires to be run throughout the system. As long as that conduit system is properly grounded, you should get an OK reading with your tester. With systems that use non-metallic flexible cable, (often called Romex), a ground wire must exist throughout the cable system AND BE USED as such from box to box. This grounding system must also be properly grounded at the main panel as well as to water piping with a jumper over the water meter. I have too often seen cases where the cable ground wires have been cut off short, not hooked up to anything or where cable without a ground wire has been installed.
I highly recommend that you have an electrician take a quick look at the grounding system in your home. Wayward power needs a better path to ground than you or your loved ones. Hopefully, this could be an easy fix, but you need someone to provide an eye's on evaluation of your home to determine what that solution is.
I hope this helps,