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I had a 2 prong plug in place where I needed a 3 prong. (no heavy loads, just TV and such) I read about replacing this with a 3 prong and found out the following:

  1. If the hot end to the box screw registers a voltage, then the metal box in the wall is grounded.

  2. I should use a GFCI outlet if possible in the box.

When I opened the outlet I realized that the box is too small for the GFCI outlet. Instead, I had a self-grounding 3 prong outlet.

I installed the self-grounding outlet, and tested with a circuit tester. The circuit tester lights up normal. However, my contact-less tester beeps on each hole. I also measure the following voltages:

  • Hot to Neutral - 120V
  • Neutral to Ground - 0V
  • Hot to Ground - 120V

Is this normal for a self-grounding outlet?

  • What is the resistance ~~line~~ ground to neutral? – Someone Somewhere Jun 22 at 23:07
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    do you mean hot to neutral? Can I measure this with the power on? – MadProgrammer Jun 22 at 23:08
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    Sorry; ground to neutral. Was thinking of other things. – Someone Somewhere Jun 22 at 23:09
  • I will check now, I can do this with the power still on right? – MadProgrammer Jun 22 at 23:11
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    Yes, power on is fine. – Someone Somewhere Jun 22 at 23:13
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So you have metal boxes? The findings of 120 V hot to ground, 120 V hot to neutral, and low resistance neutral to ground are consistent with separate ground and neutral paths to the panel and that is almost certainly what you have.

The ground and neutral are supposed to be connected in the panel and only in the panel. If that is what you have, the resistance you measure between neutral and ground at a receptacle is the lengths of neutral and ground wire back to the panel where they are connected.

EDIT

You need to determine that there is a separate ground path (metal conduit or a ground wire) all the way to the panel. The other possibility consistent (I think) with your measurement results is that someone has connected the grounds of the each receptacle to the neutral in each box. I think this is called a "bootleg ground" and it is not according to code and not safe. I think you would see evidence of this inside the boxes.

Time for you to take pictures of the inside of one or more boxes and attach the picture to your question. Also time for one of the experts to comment.

EDIT2

Bootleg ground wiki. You could take off one or more faceplates on receptacles. You could take off the "dead front" on your panel and see if you have ground wires there. Of course, you could be grounded via conduit.

  • This makes sense Jim. What baffles me is that other outlets are not measuring 120V hot to ground. And yes, I have metal boxes - at least its metal on this outlet. I havent looked at others yet. – MadProgrammer Jun 22 at 23:57
  • What are you getting for hot to ground at these other outlets? Do these other outlets have grounded receptacles? When was this house built? Was it in the time that receptacles were not grounded, i.e., two slots neutral and hot? – Jim Stewart Jun 22 at 23:59
  • Ok, checked again. Looks like If I wiggle my probe I do get hot to ground 120V. The house was built 1930 which I'm pretty sure is pre mandatory 3 prong. – MadProgrammer Jun 23 at 0:04
  • You need to determine that there is a separate ground path (metal conduit or a ground wire) all the way to the panel. The other possibility for your measurement results is that someone has connected the grounds of the each receptacle to the neutral in each box. I think this is called a "bootleg ground" and it is not according to code and not safe. I think you would see evidence of this inside the boxes. – Jim Stewart Jun 23 at 1:02

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