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Thread: Simple GFI tester question

  1. #51
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    Jun 2012
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    Quote Originally Posted by hurk27 View Post
    but this could never happen on the load side as all GFCI's have a second current transformer in them that inject a 120hz signal that will allow the electronics to detect a grounded neutral
    Hurk....

    Wow! Take a breath and let me review your post line by line and read the attachment.

    But I am puzzled by your reference to 120 Hz signal as I'm not aware of that coming from a GFCI. What am I missing, or is that contained in the attachment?
    Mike Sokol (SoundGuy)
    NoShockZone Seminars
    mike@fitsandstarts.com

  2. #52
    Join Date
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    Portage, Indiana NEC: 2008
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    @ Mike again on the post 40, after reading a little more, I agree as I said above yes the GFCI can be RPBG wired ahead of it and still function as if it was wired correctly, and as you pointed out any current flowing in any other path that do not take it back through the current coil in the GFCI will cause it to trip if it exceeds the .005 amps, but in that post you made the commit that you thought there was a way that would defeat the GFCI from detecting a ground fault, and I don't think that is passable as any current that flows from the hot through the current coil must flow back through through same current coil or the coil will develop a voltage and trip the electronics, and the fact that all GFCI devices newer then 1996 will have the 120hz injection coil that will keep anyone from boot legging the ground from the neutral any where down stream from a GFCI device whether its a breaker or receptacle device, this does not not hold true to AFCI's as they do not have the 120hz injecting coil and that is why if you have a grounded neutral on a AFCI circuit it will not trip until a load is present.

    I will say you are on top of the rest of it, and have offered some very great advice. again look over that PDF I attached to the previous post as it is a good reference for those who would like to know how a GFCI works, the writer is a very well known electronics publisher who has written many thousands of books on electronics and is most well know for his "Sam Facts" booklets that many of us used to repair anything from radios and TV's and even had a series on CB radios, and are highly sought after as they included all schematics for many of these electronic appliances.
    Wayne A. From: N.W.Indiana
    Be Fair, Be Safe
    Just don't be fairly safe

  3. #53
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    Quote Originally Posted by jmsokol View Post
    Hurk....

    Wow! Take a breath and let me review your post line by line and read the attachment.

    But I am puzzled by your reference to 120 Hz signal as I'm not aware of that coming from a GFCI. What am I missing, or is that contained in the attachment?
    sorry I get carried away some times LOL

    Yes it is in the atachment, and the next post was kind of before I seen this post
    Wayne A. From: N.W.Indiana
    Be Fair, Be Safe
    Just don't be fairly safe

  4. #54
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    Portage, Indiana NEC: 2008
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    also another little feature that newer GFCI's are required to have is they can not be reset if even there is a reversed line side neutral and hot, but this depends upon having a correctly connected EGC conductor to the GFCI device and would not apply on a two wire circuit, you can reverse the load side neutral and hot and it will still reset, but another feature is in you mix up or cross lets say put the load neutral on the line side neutral terminal and the line neutral on the load side terminal it will also not reset, but I have found a few GFCI receptacles that were made in China that have got past customs as they are clearly boot legged UL stickers on them that do not have these required features and I sent them to UL to investigate them.
    Last edited by hurk27; 07-06-12 at 11:33 PM.
    Wayne A. From: N.W.Indiana
    Be Fair, Be Safe
    Just don't be fairly safe

  5. #55
    Join Date
    May 2007
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    917

    RE: 120 Hz current injection

    You might find this link interesting. About midway down it talks about a how else this is commonly done.

    http://www.idea2ic.com/GFI/GFICs.html

    I came across this after having reverse engineered a Leviton 7599 GFCI and finding that the 200:1 coil was not connected as shown in the LM1851 doc that is commonly viewed.
    I measured the voltage across that coil and it was not 120Hz so that is what got me looking for how else it worked.
    - Resistance is Futile ..... (if less than < 1 ohm) -

  6. #56
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    Quote Originally Posted by ELA View Post
    You might find this link interesting. About midway down it talks about a how else this is commonly done.

    http://www.idea2ic.com/GFI/GFICs.html
    This is most excellent! OpAmp theory I understand, so this schematic and explanation will plug a lot of holes in my GFCI theory. Thanks very much...

    I'm happiest when I'm learning something...
    Mike Sokol (SoundGuy)
    NoShockZone Seminars
    mike@fitsandstarts.com

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