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Thread: Floating Ground

  1. #1
    Join Date
    Jun 2017
    Location
    Norwalk CA US
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    2

    Floating Ground

    My house old built 1957 is 2 wire with a ground wire that is in the attic going wherever.
    I added some lights in the bath and discovered I have a floating ground measures 120VAC no load 12VAC loaded it gives a jolt. I refered to the code when adding 2 conductor with ground to existing 2 wire no ground bond the grounds to the box and fixture I did. found the ground unloaded has 120 VAC and ohms out at 9.6 M Ohm.
    Not exactly sure of the proper way to deal with this.
    I Could add a light in series on the ground wire I m sure this isn't ethical practice.
    Any feedback is appreciated.

    Regards,

    Mike SO Cali

  2. #2
    Join Date
    Jan 2009
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    3 Hr 2 Min from Winged Horses
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    Let’s forget about the ground for a sec.

    You measured with no load as in line to neutral, correct. Load is off.

    With load you measured the same way, as in across the load while it is on, line to neutral, correct?
    "Electricity is really just organized lightning." George Carlin


    Derek

  3. #3
    Join Date
    Jun 2015
    Location
    texas
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    1,697
    Quote Originally Posted by monsagrati View Post
    My house old built 1957 is 2 wire with a ground wire that is in the attic going wherever.
    I added some lights in the bath and discovered I have a floating ground measures 120VAC no load 12VAC loaded it gives a jolt. I refered to the code when adding 2 conductor with ground to existing 2 wire no ground bond the grounds to the box and fixture I did. found the ground unloaded has 120 VAC and ohms out at 9.6 M Ohm.
    Not exactly sure of the proper way to deal with this.
    I Could add a light in series on the ground wire I m sure this isn't ethical practice.
    Any feedback is appreciated.

    Regards,

    Mike SO Cali
    Monsagrati, I reviewed your other post from a thread titled "Home Grounding" that was closed by Little Bill, and I believe that thread is related to this one.

    In that thread, you mentioned that the bath and kitchen had a reno and that there were wires attached to insulators in your attic that you believed was for lightning strikes and in this one you are referencing this same wire and now bath lights. If the wire is cloth covered it is knob and tube that could be now live/you may have inadvertently tied something together somewhere. If the wire is plastic coated or bare, it is likely a separately run egc (old practice from when first egc reqs hit the scene) that is now live from something thats been done...

    You complain about the lack of a good egc and there are really only 2 ways to get that: either run new circuits from panel to where needed or follow 250.130(C)- its dangerous to try and use an unverified conductor as an egc.

    All that said, its prolly a good idea to have an ec come look at your work- not being rude, just think its in your best interest.

  4. #4
    Join Date
    Apr 2009
    Location
    Williamsburg, VA
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    5,271
    Adding a light in series with your ground will not due anything good if you have current on it; it'll actually make things worse as you would be increasing the resistance of the circuit. That said, using an incandescent light (temporarily, as a test instrument) would tell you if your voltage readings are true or phantom.

    As user 100 wrote, the wiring on insulators in your attic is probably old knob and tube. Even if it were lightning protection, I dont believe that is tied to the electrical ground and thus back to the service, so it's no good as a fault-clearing pathway.

    The best way to deal with adding lights to existing two-wire circuits is using trims that are all plastic and do not have an EGC (double insulated), using GFCI protection, or running a new 3 wire cable from the panel. Tying any ground wires included on the lights to the ungrounded metal boxes is useless (in this case); those old boxes are not bonded back to the service. Your reading of 9,600,000 ohms is proof that you have no ground path. A proper path with have in the neighborhood of a hundredth or less of an ohm.

    The ground wire is only used under fault conditions and you should not feel a jolt while touching it or the metal frame of the fixture while the light is on (or off). Getting shocked here is an indication of another problem, perhaps a defective fixture, improper neutral to ground bonding, or wiring with failing insulation.

    Also as user 100 wrote, I think you'd benefit from having another electrician evaluate your situation. Like he wrote, no offense intended, just that this particular problem seems to be a bit outside your regular electrical work and knowledge.
    Last edited by JFletcher; 01-10-18 at 02:25 AM.

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