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iLearn

join:2013-01-16
canada
reply to iLearn

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

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.



leibold
Premium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:10
Reviews:
·SONIC.NET

Regardless what potential you are using as your reference (neutral is often used as 0V reference in the context of line voltage AC) the voltage on hot and neutral will be different (by about 120V in a North American household).

Any current coming from the power source (utility, generator) through the hot wire to the load needs to somehow return to the power source to complete the circuit. The normal return path is the neutral wire which carries the exact same strength current in the opposite direction. In a ground fault situation a portion of the return current takes an alternate return path (ground wire, water pipe, moist soil, ...) which causes the current in the hot wire to be different from the current in the neutral wire. Even a slight difference in currents is sufficient for the GFCI to trip.
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garys_2k
Premium
join:2004-05-07
Farmington, MI
Reviews:
·Callcentric
·callwithus

1 recommendation

reply to iLearn

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?

iLearn

join:2013-01-16
canada

Thank you. I understand it now.


lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1

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.

iLearn

join:2013-01-16
canada

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


Bob4
Account deleted

join:2012-07-22
New Jersey
Reviews:
·Optimum Online

1 recommendation

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.