GFCI operation question

On Sun, 01 Oct 2006 21:30:31 -0400 snipped-for-privacy@aol.com wrote:
| On Sun, 01 Oct 2006 17:14:18 GMT, "Member, Takoma Park Volunteer Fire
| |>What makes you so certain that a GFCI circuit breaker does not open the |>neutral? Have you checked with several manufacturers. | | Square D doesn't |
http://members.aol.com/gfretwell/gfci.jpg
| | There is no real need for it in a breaker since you know which leg is | hot.
MAYBE there is no real need for it. The fact that GFCI receptacles ARE opening the neutral because of the chance of miswire or usability on old wiring like K&T, we might not know if there are hazards to leaving the neutral connected. Statistics for this would also be harder to gather since if there are such hazards, they would be less often and/or less severe than with the hot left connected.
Still, I personally believe there is a small NON-ZERO hazard, generally associated with other faults or conditions. One is the possibility of higher than expected voltage on the neutral due to a loose/open neutral condition upstream. The other is that even with a normally very low neutral voltage, a solid fault from neutral to ground could still pull the 6ma that would trip the breaker. The hazard exists *IF* the breaker would continue to be activiting its mechanism to open the circuit even after it is already open, if the mechanism is not rated for continuous duty heat dissipation.
And speaking of heat, look forward, post 2008, for a lot of new home panels, the ones now FULL of AFCI breakers, to be more crowded with pig-tail wires, AND getting extra hot due to all those AFCI breakers continuously (24x356xN) using a small bit of power.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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In alt.engineering.electrical Member, Takoma Park Volunteer Fire Department
| What makes you so certain that a GFCI circuit breaker does not open the | neutral? Have you checked with several manufacturers.
I've looked at the engineering diagrams, cut-aways, and schematics. There are no contacts for interrupting the neutral wire.
| One reason why it might be OK for a breaker to leave the neutral alone | is that it is far less likely and in fact rather difficult for a breaker | to be revere wired. When a breaker type GFCI operates it will nearly | always open the ungrounded conductor. There are a lot more ways a | receptacle type of GFCI can be supplied with the ungrounded conductor | controlled by the grounded conductor leg of the GFCI mechanism.
So basically, there is no goal or interest in specifically opening the neutral. It's just a case of opening both in situations where either might be the neutral.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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wrote:

Let me say what I said another way. GFCI outlets and circuit breakers measure if there is a difference between the amount of current going throught the hot wire and though the neutral wire. If they are the same, the gfci sees no problem. Having a loose connection does not mean that will happen. Using an appliance that shorts to your body and from there to some other path than the neutral wire *would* cause it to trip.
OTOH, if you took two all-metal screwdrivers, one in each hand, and stuck one into each of the slots in an outlett, even a GFCI outlet, you could burn your heart to a fine grey ash, and the breaker would not trip. Because the same amount of current was going through the two conductors.

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Methos wrote:

There's all kinds of "bad connections". If the bad connection resulted in a difference of 5 mA or more between the current in the neutral versus the current in the hot wire, the GFCI would trip. The example you gave would not cause the GFCI to trip.
Ed
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As others have mentioned, a GFCI would probably not trip. They sense current differences, and usually have current overload sensing in them also. But a bad connection causing the terminal to warm up would not trip it unless it got very hot, and even then the results are indeterminate.

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So far there has been a lot of misinformation in replies to this thread.
Only the smoke will indicate a simple HOT connection. If there is any arcing a AFCI should detect the fault and disconnect.
Quote
"The AFCI is an arc fault circuit interrupter. AFCIs are newly-developed electrical devices designed to protect against fires caused by arcing faults in the home electrical wiring."
****
A GFCI will only protect from differences in the current flowing in the two conductors beyond the GFCI. It will cutoff the current when a very small current difference, 5 or 30 ma., is detected and should do it quick enough to save a person from electrocution.
Neither device is intended to protect from voltage spikes and neither device can detect a simple hot connection.
A hot connection alone will not csause a difference in current between the 2 legs of the circuit, only a ground fault can cause that and a GFCI should detect that.
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John G

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