For the reasons others have mentioned - by making the test current flow from one "line side" terminal to the opposing "load side" terminal the current during a test with the unit's test button does not depend on an EGC being present, but still puts an unbalanced "real current" through the sense coil for the protective circuitry to actually respond to what it sees as a real condition and is not a manual activation of the trip mechanism.Just an FYI, while the test button on the GFI receptacle will function properly but some plug-in testers may not work if the EGC is not present
It is slightly more than manually operating the trip components.
It tells the microprocessor to do what it would do if an arc signature was detected. So it at least tests that the processor is still running at least part of its control program.
AFAIK it does not test the sensor used by the processor to detect the arc signature.
If the device includes a class B GFCI, I do not think that it separately tests that function.
Not sure about the test button on an AFCI breaker with Class A GFCI.
Tapatalk!
It is slightly more than manually operating the trip components.
It tells the microprocessor to do what it would do if an arc signature was detected. So it at least tests that the processor is still running at least part of its control program.
AFAIK it does not test the sensor used by the processor to detect the arc signature.
If the device includes a class B GFCI, I do not think that it separately tests that function.
Not sure about the test button on an AFCI breaker with Class A GFCI.
Tapatalk!
How does test button on a gfci with no EGC work, How does it put a unbalanced load on the sensing coil ?
So how do we really know the test is confirming that we have the "alleged" protection being offered.
Thanks for the diagrams.:thumbsup:It puts a load on the circuit with one leg not in the detector coil which shows up as an imbalance. Here is the circuit.
View attachment 10185
Thanks for the diagrams.:thumbsup:
It puts a load on the circuit with one leg not in the detector coil which shows up as an imbalance. Here is the circuit.
View attachment 10185
Most GFCI's open the neutral when tripped, which this diagram does not show. I know receptacle types generally do and would assume circuit breaker types do as well.
Domnic,How does test button on a gfci with no EGC work, How does it put a unbalanced load on the sensing coil ?
You may well be correct that no OEM has assembled the TEST circuit as a discrete conductor passing through the current sensing transformer as the diagrams illustrate.I doubt that any receptacle type GFCIs have a third wire pass thru the current transformer because it makes no sense from a manufacturing perspective. Thus, I see no reason to show the schematics as they are drawn.
But whether via one wire or two, same current still passes through the CT.You may well be correct that no OEM has assembled the TEST circuit as a discrete conductor passing through the current sensing transformer as the diagrams illustrate.
However, from a teaching perspective to someone who is working with a beginning of Kirchoff's Laws, and who isn't going to spend time with Thevenin Equivalents, having a graphic image of current path helps to de-mystify the "Black Box" of a GFCI.
Nice photo study of the Leviton 7899. Thank you for the careful exposition.