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Discussion Forum

Grounded outlet in ungrounded box?

DanH | Posted in General Discussion on March 14, 2009 09:36am

You’re saying the old stuff is metalic armor (so-called BX)? If so then you definitely should connect the ground wire in the new romex to a grounding terminal (ie screw in a threaded hole in the back of the box) in the old boxes where you make the connections, and should connect the ground wire of the romex to the ground terminal of the new outlets.

If you don’t have metalic armor (or some other continuous ground connection back to the breaker panel) then you shouldn’t use grounded outlets, or you should uses GFCIs labeled “No equipment ground”.


The modern conservative is engaged in one of man’s oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
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Replies

  1. JTC1 | Mar 14, 2009 09:45pm | #1

    What DanH said, with one addition.

    The metal boxes which you have in the walls may be old enough that they do not have a threaded ground screw hole in the back of the box.

    You can attach the ground wire to the box via a "ground clip" which is a small, green, metal clip which grips the wire and slides over the exposed front edge of the box. Ground clips are readily available at BB or electrical supply houses.

    Or, you can bore and tap your own ground screw hole - 10-32 machine screw tap.

    Before doing any of this, I would ascertain that the box(s) in question is indeed grounded via the metallic cable covering. If not grounded - back to what DanH said.

    Jim

    Never underestimate the value of a sharp pencil or good light.
  2. HansonConstruction | Mar 14, 2009 10:41pm | #2

    It is old armored cable, so it is not grounded. That being the case, if I use new three-pronged outlets (which won't be grounded), how is that any worse than the old two-prong outlets, which weren't grounded either? Thanks.

    1. JTC1 | Mar 14, 2009 11:09pm | #3

      >>It is old armored cable, so it is not grounded.<<

      Maybe yes and maybe no.

      From your description it is the old two wire armored cable, without even the little #16 ground wire (circa 1950)

      Only reliable way to tell is with a meter at each box.

      Measure voltage from: Hot to Neutral; then Hot to Box &/or metal cable sheath.

      Compare readings, if the voltage matches - the box is grounded via the metallic cable sheath. Think metallic conduit that happens to flex.

      Required Disclaimer: I am not a licensed electrician, but I fix some of their work.

      JimNever underestimate the value of a sharp pencil or good light.

    2. DanH | Mar 15, 2009 12:00am | #4

      It is illegal and dangerous to use 3 prong outlets on an ungrounded circuit, unless the circuit is GFCI protected.
      The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

    3. brucet9 | Mar 15, 2009 04:04am | #5

      "I use new three-pronged outlets (which won't be grounded), how is that any worse than the old two-prong outlets, which weren't grounded either?"When a person sees a three-prong outlet, he may reasonably assume that it is a grounded outlet. By using it, devices that require grounding may be damaged. A motor driven device, if it has a ground fault, could have surfaces electrically charged without popping the breaker; clearly dangerous for the user. BruceT

      1. DanH | Mar 15, 2009 04:47am | #6

        Yeah, most seriously, a device with a grounded plug need not be "double insulated", and is far more likely to have a hot-to-case short. Without a good ground the case can become "hot" and create an electrocution hazard.
        The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

      2. oops | Mar 16, 2009 07:43pm | #16

        A little off the subject. Reading this made me think of the adapters I've seen that you use to plug a grounded appliance into an ungrounded receptacle. (i.e. two prong male/three prong female with the little green ground wire.) How is this suppose to make it safe. What/where should the green ground wire be connected. Just curious.

        1. DanH | Mar 16, 2009 07:55pm | #17

          The theory is that the box is grounded (via, eg, the armor on armored cable) and connecting the wire to the cover screw will thus produce a properly grounded outlet.Like I said, this is just a "theory", often disproven in practice, which is why the adapters are commonly called "suicide plugs".
          The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

  3. MSA1 | Mar 15, 2009 05:35am | #7

    If the wire is run in BX check continuity. We were able to use grounded receptacles throughout one of our houses without rewiring thanks to the BX.

    The BX casing can act as the ground. This was inspected and approved.

     

    Family.....They're always there when they need you.

    1. HansonConstruction | Mar 15, 2009 04:56pm | #8

      Thanks to all for the advice. I see now the danger in putting in the three-pronged plugs. I'll consult an electrician to insure that I'm not doing anything dangerous or against code.

      1. DanH | Mar 15, 2009 05:19pm | #9

        You still haven't made it clear why, if you have metal-armored cable, you don't use that for the ground.
        The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

        1. User avater
          xxPaulCPxx | Mar 16, 2009 06:27pm | #14

          I had thought that metal armored was no longer considered acceptable for ground, that you still needed a specific ground conductor besides the jacket, as the jacket couldn't always be dependd on be be well connected electricly.

          Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!

          Look, just send me to my drawer.  This whole talking-to-you thing is like double punishment.

          1. DanH | Mar 16, 2009 07:32pm | #15

            I think for new construction what you say is true, but it's still considered OK (grandfathered) for in-place wiring. It should be checked for continuity, though.
            The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

      2. brucet9 | Mar 16, 2009 04:04am | #10

        If the boxes are not grounded, you can still get new 2-blade outlets to replace worn out ones. Not at big box, but likely available at a good electrical supply house.BruceT

        1. DanH | Mar 16, 2009 05:49am | #11

          I've seen them at HD.
          The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

          1. brucet9 | Mar 16, 2009 07:18am | #12

            "I've seen them at HD."Not around here. I have to get them at Hank's Electric. I guess there are regional differences in what the HD stores stock.BruceT

          2. DanH | Mar 16, 2009 03:07pm | #13

            Thing is, you likely won't see them unless you're looking for them, and even then it's a needle in a haystack.
            The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

  4. glatt | Mar 16, 2009 08:32pm | #18

    "If you don't have metalic armor (or some other continuous ground connection back to the breaker panel) then you shouldn't use grounded outlets, or you should uses GFCIs labeled "No equipment ground"."

    This is kind of timely for me. Yesterday I was upgrading some of the wiring in my house. A couple of the very old circuits are ungrounded non-metallic. In the basement, the washer was plugged into an ungrounded three prong outlet. As I took it apart to replace it with a GFCI receptacle, I saw that the neutral wire went from the 3 prong receptacle to the mounting screw that held the box to the concrete block wall, and then tied into the neutral wire in the cable. The box was all rusty from the damp conditions. This means that when the washer was in use, this exposed metal box on the wall was energized, right? It had been that way since we bought the house ten years ago. I knew the outlet was ungrounded, but had no idea the box itself was tied in to the circuit.

    Was it ever common to bond the neutral to the box? This just seems crazy to me.

    I moved the box (a new one) up to the side of a dry floor joist, replaced the receptacle with a GFCI one, and labeled it "no ground."

    1. DanH | Mar 16, 2009 08:36pm | #19

      Well, while it's illegal for a number of reasons, it would probably be safer in that particular situation to tie the ground to the neutral wire than to leave the washer ungrounded. Why they'd tie the box to the neutral and then not tie the ground pin on the outlet to the box, though, I don't know. It may be that the outlet was being semi-adequately grounded through the mounting screws.
      The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

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