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Thread: Ground fault interupter question

  1. #1
    DIY Member RRW's Avatar
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    Question Ground fault interupter question

    This should be simple but I gotta ask. As I understand it, the gfi kicks in if there is an imbalance in current betweeen the hot and neutral. This being the case could a person receive a strong shock by being in the circuit between the ground and neutral and not trip the gfie? In other words, does the current need to be diverted away from the the neutral in order to trip the gfi?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    If your house is wired properly, ground and neutral are bonded together at the power entry panel, so there should be no current between the two. A GFCI doesn't monitor the ground and in many cases, you can install them without one attached at all in older installations where there may not be a ground. So, if you were injured by current on the ground OR neutral, it would be a fluke that the GFCI couldn't help you with. You're right, it looks for an imbalence between the hot and neutral, and (most?) trip at about 5ma of current; far less than what it takes to kill or injure a healthy person.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member RRW's Avatar
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    Thanks Jim, Well, I goofed up the question . It should have said "between the hot and neutral" rather than what I said. I think you answered it anyway. Regards, RW

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    Yes the current would need to flow through your body. Then the GFCI would trip turning off the electricity. BUT this happens SO fast, you don't even notice it!

    People frequently have faulty handheld appliances plugged into a GFCI. The GFCI keeps shutting off. They think something is wrong with the GFCI. They replace the GFCI - same problem. The problem is with the appliance (which is shocking them)! The GFCI is doing its job.

    RCD/GFCI...
    http://en.wikipedia.org/wiki/Residual-current_device

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    Electrical Contractor/Instructor jwelectric's Avatar
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    If the current is flowing from the hot to the neutral through your body the GFCI
    WILL NOT OPEN!!!!
    It will see your body as any other load that would be plugged into the receptacle or on the circuit.

    GFCI devices will not keep you from being electrocuted unless you are between the hot and the equipment grounding conductor or another conducting body that serves in place of the equipment grounding conductor.
    Should you remove a GFCI receptacle from its enclosure and grasp the device between your forefinger and thumb from the hot to the neutral the device would look at the connection the same as anything plugged into it and would not open.

    The job of a GFCI device is contained in its name, GROUND FAULT circuit interrupter.

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    DIY Member RRW's Avatar
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    Thank you Mr. Marne, that is a definitive answer. So there is basically no protection from cross or should I say within circuit shocks. I know I have received some pretty severe shocks and it never tripped the breaker either.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The device is looking for an imbalance. That means that some of the current that is normally on the hot to neutral connection is leaking to ground somehow. In that case, something is wrong (a fault) and some of the current is leaking to ground. If it was a straight short, it would likely trip the breaker, but more often, it is much less current. the GFI portion is pretty quick to respond.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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