Thread: GFCI outlets
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Old 11-06-2018, 02:08 AM   #14
Qurich
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Join Date: Sep 2018
Location: New York
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There is no interaction between one GFCI and another, unless one is faulty in some ground-faulting manner. Set that idea aside and let's imagine some scenarios where all the branch circuit wiring and GFCIs are good.

The GFCI receptacle will trip with a leakage, let's say, of 5.12 milliamps that can come from whatever is downstream of it.

The GFCI breaker will trip, let's pretend, at 5.3 milliamps.

Now the branch circuit has a couple other outlets on it between the GFCI breaker and the GFCI receptacle, and the branch circuit conductors are each about 55 feet long between the breaker and receptacle. There will be a capacitive "leakage" to ground along the 55 feet. Lets say that is 0.1 milliamp.

If no load is connected to any of the outlets between breaker and GFCI receptacle, and a ground fault downstream of the GFCI receptacle of 5.15 milliamps occurs, the receptacle will see 5.15 milliamps, and the breaker will see 5.25 milliamps. The receptacle will trip.

Now, let's add a cord and plug "thing" to one of the intermediate outlets between the GFCI breaker and the GFCI receptacle, a thing that has a ground fault "leakage" of 0.2 milliamps. Now, a ground fault through the GFCI receptacle of 5.05 milliamps occurs, the GFCI receptacle will see 5.05 milliamps and not trip, and the GFCI breaker will see 5.35 milliamps and the breaker WILL trip.

Moral of the story: It's hard to know, without careful circuit analysis, which GFCI will trip. The end user will probably find their behavior to be a mystery and hard to live with.

I currently have 2 dedicated 120v/20 amp circuits that have 20 amp GFCI receptacles (these). After some thought and consideration I realized it would be quite difficult to test/reset a faulted GFCI outlet as my tank/stand is about 43" from the receptacle and I would be leaning across a 36" wide sump.

So I went and bought two Square D Homeline 20-Amp Single-Pole GFCI Circuit Breakers https://besttoolexpert.com/gfci-outlet/ (my sub-panel is a Square D Homeline model).
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