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Thread: Doubt About testing EGC

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    Doubt About testing EGC

    hello !
    I was studying aspects of grounding systems and watching videos in youtube i found something interesting that i would like to understand...

    the video is about testing the grounding in a house.... everything was good until the guy disconneted the EGC for the test and measured a voltage (15 V aprox) between the hot and EGC entrance in the receptacle....

    the question is: what is the explanation of this voltage if the EGC was disconnected ??...
    here is the link in youtube.... i invite you guys to take a look to the video and if it is possible, give me an explanation about it...


    https://www.youtube.com/watch?v=QIdComJj7QU&t=7s

    Thanks....

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    Don't need the video. A high-impedance voltmeter does not provide enough of a load to prevent itself from measuring induced (phantom) voltage.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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    Quote Originally Posted by LarryFine View Post
    Don't need the video. A high-impedance voltmeter does not provide enough of a load to prevent itself from measuring induced (phantom) voltage.
    +1, did not look at video myself, but not sure why you would disonnect the EGC and then test from the hot to it even with a low impedance meter, what is that measurement going to prove other then possibly something that indicates "open ground" which you intentionally created?
    I live for today, I'm just a day behind.

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    Exactly Sir.... I agree with you... but the thing is that there is a voltage.... please take a look to the video.. and see what i mean
    thanks for your time!

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    Quote Originally Posted by Orestes.Cubas View Post
    Exactly Sir.... I agree with you... but the thing is that there is a voltage.... please take a look to the video.. and see what i mean
    thanks for your time!
    Had he used a low impedance meter he wouldn't have had a reading from Hot to the open ground.

    When he uses the term "earthing" he is talking about what we call the equipment grounding conductor here.

    Only thing he has proven is that the "earth" conductor in his application is connected to the the grounded (neutral) conductor at some point upstream, nothing he has measured tells us if it is connected at a point where it isn't supposed to be connected, or that it actually is "earthed" anywhere.
    I live for today, I'm just a day behind.

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    All he did was measure voltage between the hot and a small piece of metal floating (insulated from everything.) It dodn't read zero volts because there is a small amount of conductivity (capacitance of the air) between the grounding contact and the world around the receptacle. The larger the piece of metal, the higher the voltage would be.

    It reads voltage because the meter is sensitive, meaning it takes very little current to make it show a voltage. If he had a small light bulb connected in parallel with the meter leads, it would have read zero, because of the relatively low resistance of the bulb. He could have measured from hot to his hand and gotten an even higher voltage.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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    Quote Originally Posted by LarryFine View Post
    All he did was measure voltage between the hot and a small piece of metal floating (insulated from everything.) It dodn't read zero volts because there is a small amount of conductivity (capacitance of the air) between the grounding contact and the world around the receptacle. The larger the piece of metal, the higher the voltage would be.

    It reads voltage because the meter is sensitive, meaning it takes very little current to make it show a voltage. If he had a small light bulb connected in parallel with the meter leads, it would have read zero, because of the relatively low resistance of the bulb. He could have measured from hot to his hand and gotten an even higher voltage.
    Measuring from hot to other lead in open air likely gives similar reading as he had for the disconnected EGC.
    I live for today, I'm just a day behind.

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    I can walk across a carpet on a cold winter morning and get zapped by several thousand volts. The 16V here is like...meh.

    We bond to bring things to a common potential. Remove the bond, and things will take on whatever potential the circumstances of life impose. In the case of the EGC, it's not only bonded to the GEC (and earth), but is bonded to neutral as well. In the case of the video, the presenter disconnected the EGC. This removed the bond to the ground terminal of the outlet. Removed the bond to neutral, as well as to the GEC (and earth). Now the ground terminal exists as a point in space unbonded (in the low impedance sense) to anything. It will take on whatever potential circumstances of life impose. Actually, to be more accurate, we should say it takes on a RELATIVE potential based on whatever the circumstances of life impose.

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