GFCI breakers

[Mike Bates]

I'm using a Square D NQO gfci breaker for a recptacle circuit in a bathroom 150 ft from the panel. When trying to test the GFCI protection of the circuit in the bathroom (touched neutral to ground) the breaker won't trip immediately.If i left the the N&G tied together the breaker would trip after 20-30 seconds but if i created a ground fault near the panel( j box near panel ) it would , and trip instantly. I' tried 3 seperate breakers all with the same result . i tried putting a gfci receptical inline. this would trip instantly when tested . The Breaker is a 5 milliamp trip as is the receptacle. The distance from the panel is about 150 ft, There are no shorts on the cable.Any one have any insight into this. Any help would be appreciated.
as I'm here to learn .

 

[don_resqcapt19]

Mike,
There is a time trip curve for GFCIs. You have created a parallel path for the grounded conductor current when you connect the EGC and the grounded conductor on the load side of the GFCI breaker. The amount of current that flows is based on the impedacne of the circuit. The more wire in the circuit, the less current that will flow. As you move the connection closer to the breaker the impedance goes down and the current goes up. If you have a meter that can measure AC mA connect it in the circuit at the point where you are shorting the EGC and the grounded conductor and see how much current that is flowing. The UL standard (UL 943) for GFCIs says that with a 6mA ground fault the device is permitted to take up to 5.6 seconds before it trips. The higher the current the quicker the trip. It also must not trip with a current less than 4mA. The trip time at 4mA could be as long as 10 seconds. Maximum permitted trip time =(20/mA)^1.43
Don

 

[Mike Bates]

Thanks don, That is what instinct was telling me but needed to hear it from someone.My foreman was fighting me on my "thoery" and I felt I would be better served getting a fresh pov on the matter.