MarineTech
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- Location
- Camarillo, CA
Just for reference I have included a link to the LM1851.
http://www.ti.com/lit/ds/snis158/snis158.pdf
http://www.ti.com/lit/ds/snis158/snis158.pdf
We agree and yet we do not.
Unless you are talking about times on the order of one nanosecond, the time it takes light to travel about a foot, (corresponding to a frequency on the order of 1 GHz), there is no way that the currents can be unequal at two different points in a single closed loop circuit. The electrons have to be going somewhere.
What causes the effects that you observe with spikes, inductive kickbacks, and other transients is current through relatively small stray capacitances that make no noticeable difference at 60Hz but become important at higher frequencies. So when I am talking about reactive current paths, I am including ones in the range that you would not notice unless you were specifically looking at transients and high frequencies.
Let's now assume that the exact same current waveform was applied through both windings of the GFCI current sensor. If the coils are not necessarily identical in characteristics across that wide frequency range, you could then get a non-zero difference signal. One simple way for this to happen would be if one of the coils has a little more intra-winding capacitance than the other, so some of the current at high frequency is actually bypassing the coil instead of flowing through it.
That does not change the fact that the same current is flowing in both wires, it just means that the GFCI is not well enough engineered to behave well at that frequency. And, as you point out indirectly, it is easier to use a time delay to ignore those signals than to engineer them out, especially if part of the problem is capacitive couplings within the appliance. This delay takes care of both problems with one stone.
I posted here that the GFCI can trip faster ( under normal conditions) than some were/are stating as supposed fact.
http://forums.mikeholt.com/showthread.php?t=149465&page=2&p=1445387#post1445387
I posted here that GFCI's can trip even more immediately due to EMI. In many of these cases the differential sensing core may be completely bypassed.
http://forums.mikeholt.com/showthread.php?t=152331&page=3&p=1473338#post1473338
In this thread a differential current meter should be used to confirm that excessive leakage is, or is not, present.
Point taken. Certainly the small sensor coil in an outlet-mounted GFCI works exactly as you state.
Larger imbalance detection systems at a source or breaker panel have other options, but they can also be built in exactly the same way.
Very familiar with the LM 1851 data sheet.
Like to view a link to the LM 1951 data sheet that was mentioned. Not the 1 amp switch, but a device that replaces the 1851?
I temporarily disconnected the frame ground wire from the cordset, and refer worked fine, no trip, reconnected, tripped instantly. Obvious current leak to ground. Worked good in non-GFCI protected circuit. Appliance repair company said not to put on GFCI, and after talking to 3 technicians, all with a different story on how GFCI's work, (None Correct), I finally was able to relocate the GFCI downstream from Refer, but still covering all countertop recepts. Tile Floor, now waiting for HO to get shocked. Leviton says they do not recommend them on refers, but did not say not to. How about the thousands that work OK, including mine.
I temporarily disconnected the frame ground wire from the cordset, and refer worked fine, no trip, reconnected, tripped instantly. Obvious current leak to ground. Worked good in non-GFCI protected circuit. Appliance repair company said not to put on GFCI, and after talking to 3 technicians, all with a different story on how GFCI's work, (None Correct), I finally was able to relocate the GFCI downstream from Refer, but still covering all countertop recepts. Tile Floor, now waiting for HO to get shocked. Leviton says they do not recommend them on refers, but did not say not to. How about the thousands that work OK, including mine.