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Thank you for any help or advice you can provide. I am replacing a receptacle in my basement. The first problem I noted was I had a three prong receptacle, but there was no ground wire. The main incoming wires have a ground connected in the back of the box, but the receptacle ground was not attached to anything.

After the receptacle was removed I switched the breaker on to troubleshoot why the bottom receptacle doesn't work. There are two breakers labeled basement. If I open both breakers labeled basement, no power. If the bottom one is shut with the top one open, the voltage is normal 110V. However, If I reverse it, with the bottom open and top shut I get 11 volts. What would give me the measured 11 V?

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    What type of meter are you using? How are you measuring voltage (hot to neutral, or hot to ground)? Are the receptacles part of a multiwire branch circuit? – Tester101 Feb 7 '17 at 17:50
  • You probably have a self-grounding outlet, and it's common for some residual voltage to be present on the grounding (neutral) conductor. – isherwood Feb 7 '17 at 17:50
  • I'm using a Fluke 87V multimeter from hot to neutral. Measuring the cable ends, because the receptacle was already removed. – Dustin Standel Feb 7 '17 at 18:15
  • The 87v is a high impeadance true RMS meter. These will show induced voltage if there are wires with power running in parallel. Are these 2 separate duplex receptacles or a single? Recently a member of this site installed a new outlet that the tab was broken to the lower outlet. – Ed Beal Feb 7 '17 at 19:51
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Grounding

If you have a metal box, there should be a grounding pathway to the metal box. This can be a ground wire attached to the box with a #10-32 screw in the threaded hole provided on the box; or metal conduit (but not necessarily armored cable); or a combination.

A receptacle has a set of metal ears on top and bottom. This is called a "yoke". These metal parts are bonded internally to the ground socket holes and the ground screw.

If you have a grounded metal box... and the receptacle is screwed down so that the ears bottom out on the metal box... and you have solid metal-metal contact between receptacle and box... that is a valid grounding path. It is not valid if the ears "hang up" on drywall or plaster and there's a bit of screw length. Despite being all metal, screws are not a valid grounding path.

Two breakers, two circuits

Imagine if you unfurl 500 feet of electrical wire parallel to a high tension line. Will you get a measurable voltage? You bet. You're picking it up like radio waves. Will it be useful for anything? Nope.

The same happens in wires running parallel in your house. If one is hot and you test the other, sensitive voltmeters like a DVM will see a stray voltage. It's not useful for anything; an incandescent night-light won't light up. In fact, that's a great way to arrest this stray voltage: plug a night-light into one receptacle while measuring the other.

Other than that, I would say you have a very serious problem if the socket measures 120V with one breaker on, and 0V with both breakers on. That would indicate something complicated and weird, and potentially dangerous.

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  • We'd need to know more to know if generic "BX" is or isn't a grounding conductor because people don't get the differences between various types of metal-jacketed cables -- old armored cable isn't, modern AC with the bonding strip is, MCI isn't but MCS/MCC/MCI-A is. – ThreePhaseEel Feb 7 '17 at 23:39

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