GFCI comments and questions

Any of the newer GFCIs would trip open on loss of power so opening the neutral would open the hot. With the older GFCIs your scenario might work.

In Europe, some RCDs include monitoring for loss of neutral, loss of earth connection, or live/neutral reversal, and will trip on any of these fault conditions.

We have "fail-safe" RCD's which trip on loss of power, but they aren't commonly used or found. The wiring fault conditions checked for above are treated quite separately from loss of power -- power loss does not normally trip fault monitoring RCDs.

I just had a bad GCFI breaker today, old style. It tripped with both load conductors off and the pigtail connected. Yes if you disconnect the pigtail from the neutral; bus and connect the circuit neutral to the bus it becomes a non-GFCI breaker. I doubt the new style would ever reset without the neutral pigtail connected but if it was already "on" I am not sure what would make it trip. They don't trip with a power failure.

I sort of remember taking a receptacle GFI apart some years ago and being impressed that it looked like a simple, purely magnetic, trip mechanism. That is, an unbalance of the line and neutral currents would create enough magnetic force to trip the unit. Also, I do NOT remember any electronics other than the resistor for the test. Of course those with the LED light would need another resistor and the LED. --Phil

I thought I knew what "pigtail" meant until I read this post. I am not sure now what "off" means. Does it mean disconnected or open? How would you write this up without using the pigtail and off?

Bill

-- Ferme le Bush

The GFCI breaker has a white wire permanently attached to the breaker (I called a pigtail) This connects to the neutral bus. You then connect both white and black from the load side circuit to the breaker. The power rail and the pigtail provide power for the GFCI circuitry along with the load. This one worked fine when I removed both white wires from the GFCI and only used it to source the hot leg. (circuit "white" directly on the bus) This was the old style that would reset without power to it. I have not tried the new ones in this configuration but I can't imagine how anything could trip without both sides of the power attached.. I do have the bad one here and I will open it up later tonight to see what is inside.

Really?

I have some 12 or so GFCIs in the house. We lose power on the average of once a week (semi rural location).

Trust me: GFCIs don't "trip open" on loss of power.

If they did, I would be running all over the house resetting the gadgets all the time.

Do a Google search and find a diagram. There is a "chip", a diode bridge, a few caps, and the magnetic "trip."

Among other things the "electronics" injects a common mode 120 Hz signal on the load lines so that the device can detect NEUTRAL/GROUND faults.

This is the bad one I replaced today. Manufacture date is mid 90s Square D QO 30a GFCI

I read it as the load terminals will disconnect if the line-neutral is removed (for the new GFCIs). The load-hot (and load-neutral) will be disconnected, but the GFCI will not be tripped. That is my understanding of how the new ones work (but I havn't made the simple test to see if it is true). My guess is that a 2 pole GFCI breaker would be powered by the

The new standard also prevents reverse wired GFCIs (line to GFCI load terminals) from powering the local receptacle or GFCI line terminals.

bud--

Neat!

That, of course, is a combination CB and GFCI used in the CB box. All I have are the ones that place a duplex outlet.

Isn't taking stuff apart FUN?

I haven't done that particular experiment. I just removed power and observed that there was still continuity. Since I still have my "experimental setup" nearby (tangled in misc. lamp cords, computer cords, etc), I will do some additional research this weekend.

But how can they be "disconnected" if the device isn't "tripped?"

It seems that the 120 volt jobs are ALSO two pole. Since the insert says that you don't need a ground for the device to function, to a good approximation they just don't care which is HOT and which is NEUTRAL.

Yep!

Yes Andrew but that is why I made no mention of RCDs.

You *must* modify the existing circuit, but the mod is simple - or at least it was for the receptacle circuit I used. In principle, it should be the same: limit the current through the chip and use the scr output to drive an opto which drives a triac.

Ed

This one is bad. Trips immediately when the white pigtail is connected. I would use a good one if I was building something

You can manufacture them with a DPST NO relay connecting the line to the receptacle. No line-neutral, no control power, no relay pull-in, "disconnected".

Another of the changes for new GFCIs was to be more likely to fail OFF (commonly failed ON previously). Using a NO relay may aid in that.

My intent was that a 2 pole breaker with neutral could have control power from line-to-neutral or line-to-line. My guess is it is line-to-line so it doesn't matter if the line-neutral pigtail is connected or not.

I thought GFCIs triped on reverse line-hot-neutral although it is not obvious how that would work unless they referenced the ground wire connection.

If a GFCI is tripped, is the control power dead or live?

bud--

I suppose one could make them that way. Easy to determine: just listen for the "click" when power comes back on.

Well, my OP was to question how the devices operate as NOW made.

Having a relay at the outlet is "Interesting." It reminds me of something that was proposed YEARS ago: "Smart" outlets. The idea was that each "smart" outlet would "test" the connected load for safety BEFORE permitting power to flow.

Again, my OP concerned 120 volt US standard stuff in which the neutral is bonded to ground at or near the meter or main panel.

Since they have two pole "relays" that just isn't a safety concern.

I "think" it's live. Some years ago I had a GFCI with a "pilot" light. Now they have a light that goes on if the device is "tripped" but (of course) the power is still coming in.

Has anyone taken a "new" GFCI outlet apart?

bud--

The GFCI would not lose "power" in this scenario. There is no direct connection to the gfci circuit from the line side wiring. A GFCI compares the currents on the hot and neutral. this comparison is made using coils that convert the line currents to voltages and currents utilized by the GFCI circuit. In your scenario, if someone were to come in contact with either the hot or neutral on the load side of the GFCI that creates a ground fault you would have current flow through the hot conductor and none through the neutral, the GFCI would "trip" if this current were above the set point of the GFCI, approximately 5-6 milliamps for a Class A GFCI. For a good discussion on how a GFCI works go to