GFCI Breaker Bench Testing

joes_electric

Member
Location
Tunkhannock,Pa
Occupation
E&I Tech (Retired)
I am testing a Sq-D QO 2 pole GFCI breaker on my bench. If I connect a 5.5 MA load from either hot pole to the breakers neutral or the pigtail neutral, no trip as expected. However if I connect a 6.7 MA load from either hot pole to the breakers neutral, NO TRIP. Connecting the same 6.7 MA load to the pigtail neutral WILL trip the breaker. Why no trip when the load connects to the breakers neutral? I am supplying the breaker with 220 Volts and am using 22 k and 18 k high wattage resistors as my test load. What am I missing here? Thanks...
 

retirede

Senior Member
Location
Illinois
The pigtail must be connected to neutral to power the electronics, I believe. If it’s not connected to anything when you apply leakage thru the breaker’s neutral terminal, it won’t trip.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
If I connect a 5.5 MA load from either hot pole to the breakers neutral or the pigtail neutral, no trip as expected.
It should trip with a load from either hot load terminal to the pigtail, but not to the breaker's neutral.

However if I connect a 6.7 MA load from either hot pole to the breakers neutral, NO TRIP.
That's seen as a line-to-neutral load, and should not trip the breaker.

Connecting the same 6.7 MA load to the pigtail neutral WILL trip the breaker.
Again, that's what should happen.

Why no trip when the load connects to the breakers neutral?
Again, a line-to-line or a line-to-neutral load should not trip it, only a line-to-ground (or the pigtail, neutral bus, etc) should.
 
Last edited:

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
Why would you expect the GFCI breaker to trip when you connect the resistor from the hot terminal to load neutral terminal? That is where L-N branch circuit loads would be connected. All current leaving the line terminal will be returned to the load neutral terminal (and vice versa on the other half cycle), causing no net magnetic field in the toroidal current transformer of the breaker.
When tying the resistor to the pigtail neutral, the current that it flows will not return though the transformer and therefore the breaker will trip.
 

joes_electric

Member
Location
Tunkhannock,Pa
Occupation
E&I Tech (Retired)
Why would you expect the GFCI breaker to trip when you connect the resistor from the hot terminal to load neutral terminal? That is where L-N branch circuit loads would be connected. All current leaving the line terminal will be returned to the load neutral terminal (and vice versa on the other half cycle), causing no net magnetic field in the toroidal current transformer of the breaker.
When tying the resistor to the pigtail neutral, the current that it flows will not return though the transformer and therefore the breaker will trip.
OK, this makes sense of it all. I'm not sure why I did not think of this way but Thank You for the answer...
 

joes_electric

Member
Location
Tunkhannock,Pa
Occupation
E&I Tech (Retired)
It should trip with a load from either hot load terminal to the pigtail, but not to the breaker's neutral.


That's seen as a line-to-neutral load, and should not trip the breaker.


Again, that's what should happen.


Again, a line-to-line or a line-to-neutral load should not trip it, only a line-to-ground (or the pigtail, neutral bus, etc) should.
Thanks Larry. This makes perfect sense...
 
Top