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Farmington, MI

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reply to iLearn

Re: First post - recently joined - GFCI without a ground wire

said by iLearn:

Thanks leibold and LazMan.

@ leibold - I wanted some clarification, you said 'differential in current between hot and neutral', do you mean differential in voltage instead? I am saying this because as far as I know, the neutral carries the different between the current coming in through hot and the amp (current) used by the resistance (a bulb for example). So the current flowing through the neutral will always be less than the hot wire and the GFCI will always trip, correct?

Sorry, I am just trying to get my basics right.

Think of voltage like the water pressure on a pipe system and current as the amount of water flow. The voltage (pressure) pushes the water (electricity) through the pipes (wires) but the flow (current) is the same no matter which of the series connected pipes (wires) you measured it.

Now, if the pipes should spring a leak, then the one supplying the water (electricity) will have more flow (current) than the one "downstream" (past) the leak. That leak will be bleeding off some of the flow (current) that was supposed to run through the pipe (wire). The flows (currents) in the pipe (wire) supplying the system won't balance with the flow (current) in the pipe (wire) carrying the flow (current) away.

In no case does the total pressure (voltage) really enter into it, that's what makes the flow (current) happen, but whether the leak is there, or not, the pressure (voltage) won't change much.

Does that help, or make it worse?


Thank you. I understand it now.

... of ideas
Ottawa, ON
Here is a diagram from wikipedia RCD entry and really simplified description to help you visualize what is inside a typical GFCI outlet.

Both hot and neutral (L/N) conductors pass through the core of a single current transformer (3). Ideally the currents flowing through L/N are identical and in opposite direction, so effectively zero current flows through the coil (2).

But when there is some leakage current from either L or N (to some grounded human or grounded object) the electromagnet (1) disconnects both L/N conductors from the outlet.

The ground conductor (when available) is connected straight through to the ground of the outlet. So when a GFCI outlet has tripped, ground prong is still connected to ground, but the L/N prongs are both floating.

P.S. The test switch (4) bypasses about 5mA from L to N.


ah great, now I am confused again (j/k)

Account deleted

New Jersey

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Shorter answer: With a properly-functioning appliance, the current on the hot and neutral prongs is the same. If there's a problem and the current is instead traveling through, for example, your body, the GFCI outlet will trip and cut-off the current. A ground wire is not necessary for this protection.