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OT: GFCI Breakers and Generator Transfer Switch

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  • OT: GFCI Breakers and Generator Transfer Switch

    with the nearly constant power outage we've been having over the last week, this issue has occurred with my house wiring, and i'm wondering whether we have any electricians or qualified amateurs here who can tell me exactly what is happening.

    i have a manual transfer switch installed to allow generator power feed to 10 circuits in my main load center (breaker box). the transfer switch is wired in so that each of the 10 circuits ties in before the breaker in the load center. the transfer switch has 10 separate breakers that have three positions each: line, off, and generator. when in the line position, the power is supplied from the wire coming in from the electric company. in the generator position the power comes from the generator input. when in off, no power goes to the circuit from either input.

    the one unique thing with this setup is that when i am on generator power i have 10 circuits in the house that work, and the rest do not. when the power comes back on, the 10 circuits powered by generator are still on generator power, but the remaining circuits in my house are simultaneously powered by the line coming in. this all works fine with the exception of one circuit. one of the 10 circuits routed through the transfer switch has a gfci breaker in the load center. this circuit never poses a problem when on only line power or generator power, but when it is on generator power and the main line comes back on, the breaker immediately trips.

    i can see nothing that is done wrong with the wiring in the house or to the transfer switch, so i have been wondering why this always trips. the only thing i can think of is that because the generator carries a neutral line back to the transfer switch when powering the circuit, the breaker is basically seeing two different neutrals when the main line comes back on. i believe a gfci looks for a difference between the hot and neutral, so would this account for my phenomenon? i can't figure out any other reason for this, and i can't see any way it would all work under normal circumstances if it wasn't properly wired.

  • #2
    The "common" neutral is likely your problem. Even without wiring like your generator, GFCI require a separate (verses "shared") neutral. You find this the hard way when trying to add a GFCI to 3 wire 120v distribution.

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    • #3
      I think GFIs are designed to require power to energize the relay coil- thus when power fails, the circuit is interrupted automatically. No power is needed to maintain the off condition. When power is restored, it seems prudent that a human input would be required to trip it on again. You would not want to automatically re-power a circuit which may have been responsible for the disconnect in the first place. I realize that your condition is not a fault downstream of the GFI, but the action would be the same.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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      • #4
        No GFCI that I use is like that. Power can go on or off at will. If they are tripped due to a current imbalance, they will of course stay tripped.

        Comment


        • #5
          Originally posted by darryl View Post
          I think GFIs are designed to require power to energize the relay coil- thus when power fails, the circuit is interrupted automatically. No power is needed to maintain the off condition. When power is restored, it seems prudent that a human input would be required to trip it on again. You would not want to automatically re-power a circuit which may have been responsible for the disconnect in the first place. I realize that your condition is not a fault downstream of the GFI, but the action would be the same.
          it only trips when both generator and line power are both on simultaneously. if it's just a case of a power failure with no generator input when the power is restored, there is no issue with the breaker tripping when the power comes back on. it has happened before in previous years, but i took it as an anomaly due to me toggling between line and generator. it's only now that i've been home over the holidays and that i've see it happen every time that the generator is on that i'm seeing the issue as a regular issue. constant tripping is bound to weaken the breaker prematurely. looking at it now, i can't figure out why there is even a gfci breaker on this circuit snce it's for a bedroom - i thought it was the circuit powering the whirlpool tub, but that's on a different gfci. (maybe that's all the electrician had left on him that day?) or, it's possible that circuit powers the light over the shower i the bathroom next door? i'll have to see if i can isolate everything on that circuit and maybe do a little rewiring to eliminate the need for the gfci.

          Comment


          • #6
            What's happening is that the GFCI breaker has a "sense wire" connected to the neutral side of your main panel. When the hot side is powered from the generator side of the transfer switch and the power comes back on, the GFCI senses the difference between the utility return and the generator return, thinks there is a fault, and trips.
            Kevin

            More tools than sense.

            Comment


            • #7
              The principle of the GFCI is to compare the current on the hot lead to the current on the neutral. If they do not match to a low number of milliamps (thousandths of an amp) the thing trips.

              Any externally "injected" current that travels through the neutral wire of the GFCI will cause an instant trip. Would be the same for the hot wire, but we presume that is isolated.

              Therefore, there must be some way for "extra" current to travel over the neutral through your GFCI when both sources are "on".
              1601

              Keep eye on ball.
              Hashim Khan

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              • #8
                A GFI requires two conditions to operate. An imbalance of line and neutral currents and the presence of line-neutral voltage to power it.

                I suspect the transfer switch is simply switching the circuit 'live' between the GFI output and the generator output.

                When operating from the utility power the GFI simply operates as designed. When operating from the generator with no utility power present, only the neutral current flows through the GFI but it doesn't trip because it has no line supply (from the utility).

                When the utility power is restored the GFI receives a power supply, and immediately detects the imbalance.

                Note: If this is the problem, then the GFI is NOT providing protection when operating under generator power.

                Cheers

                .

                Comment


                • #9
                  I'd have to think for a minute if a bond between the neutral on that ckt and the ground on that generator (which is bad), could cause something similar while the generator is running but not when its off. I think you'd need a ground current at the generator (which in itself is probably a bad thing) AND that particular wiring error at the same time.

                  Or maybe somebody bonded the neutral and ground at the generator AND did the same mistake on that branch, so you won't find a wire between two branch neutrals, its actually the ground thats acting like a wire. Which is really bad, BTW. Fix one mistake and the symptom will go away until someone gets electrocuted, so if you find one bond you should try to find the other also.

                  I wonder if RF noise / induced current noise from the generator ignition ckt could be strong enough to confuse the GFCI. 20 years ago one of my fathers ham radio friends found out 1500 watts of RF could thoroughly confuse a 1990s vintage GFCI, or maybe there was some rectification component such that the line/neutral currents really were genuinely outta whack and the GFCI was doing the right thing, never really heard how that turned out. Ferrite core would have to be too big for power lines, right? Probably easiest to change the wiring such that its not a perfect quarter-wave length at 80 meters band or whatever.

                  The other guys are probably 99.9% odds to be correct about a shared neutral but my crazy ideas could be a possibility if the simple shared neutral doesn't pan out. Electrical puzzles are fun, especially the weird ones! Be sure to post back when its figured out!

                  Comment


                  • #10
                    Is the neutral grounded in the genset and then also switched in the transfer switch? If your xfer switch is a 3 pole and the neutral is being switched then the genset neutral *must* be grounded in the genset or transfer switch.
                    If the neutral is floating at the genset then your transfer switch should be only a 2pole and the neutral will be common throughout your system and should be grounded at the point of your service entrance only.
                    That would be the first thing I investigated, I have seen more than a few times where a genset with a grounded neutral is used in a 2 pole (assuming single phase) xfer setup, however the neutral should only be grounded at one point, the point where the main breaker or fuse is. If it is grounded at the genset and you only have a 2 pole xfer switch just remove the ground screw in the genset, its typically a brass screw and is labelled in the documentation.
                    If that checks out check for clean switch contacts in the transfer switch, if its made with moulded case switches there is not much you can do but look for signs of excessive carbon around the vents on the switches as well as any signs of heat. Then you should check all the connections and make sure they are snug and clean.
                    I am an electrician.
                    Let us know what you find.
                    Cheers,
                    Jon

                    Comment


                    • #11
                      without having tested it yet, i'm betting that it is a case of the generator having the neutral bonded, as a couple of you have suggested. i've done a little more searching, and this seems to come up as a common issue. this was all set up before i lived in this house, but it was family that had the work done about 12-15 years ago. i remember the electrician who did the work, and i thought he was a fairly reputable one, although the first time i had the panel apart i found one pair of wires for the transfer switch twisted and black taped (apparently someone ran out of wire nuts that day?).

                      at the time of the generator installation, the gfci breakers wouldn't have been in the panel, so the issue would not have been noticed, though i know for a fact that the generator had been purchased and was available for the electrician to hook up to, because he made a short cord with the proper plug to connect at the receptacle on the outside of the house. i assume that you weren't supposed to have multiple ground-neutral bonds then either? - we're talking 1998-1999 era. i know codes change pretty regularly, so maybe he did it by the code at that time?

                      the same electrician was the one who did the remodeling to the bathroom and master bedroom just prior to my moving in (2006), and at that time the gfci breakers were installed. this was when i would think he would have known that the gfci breakers would have posed a problem. my generator is technically a portable, though i can't remember the last time i took it anywhere else to use. regardless, i think, actually, i know that if i remove the ground-neutral bond at the generator i'll forget about it and murphy's law will rise and bite me in the backside when i use it for something else and forget about that screw i removed. it looks like there is a switched neutral kit available for about $100 that will take care of my problem without modifying the generator. it's only 8 circuits and my transfer switch is 10, but that won't be an issue because 2 of the circuits run my well pump, so that's two that don't require a neutral.

                      i'll have to confirm this of course, but if i were a betting man, this is where i'd put my money. also, i've been threatening to do a little creative wiring in the house too. i'm not happy with the way a lot of the circuits are wired, with respect to what's on them. when the bathroom was remodeled, the light above the mirror and the receptacles above the sink were wired in with a spare bedroom on one side of the bathroom, instead of with the rest of the bathroom. now that i've also found a gfci breaker for the master bedroom, it's either not needed, or it powers the new light over the shower in the bathroom. it's beginning to look like i've got 4 separate circuits powering my bathroom - ceiling lights and wall outlet on the bathroom circuit, wall lights and sink outlets on the spare bedroom circuit, whirlpool tub on its own, and light over the shower on the master bedroom circuit - when it could have been on one, or two max. thankfully the house is a ranch with a full basement. a good portion of thef the wiring is accessible.
                      Last edited by lost_cause; 12-31-2013, 01:22 PM.

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                      • #12
                        If the neutral is bonded at the genset then my recommendation would be to remove it. Tyrap the screw or a note to the hitch on the genset so if you ever move it you will remember it.
                        In my opinion it is a better arrangement to have the neutral floating at the genny and bonded at service entrance.
                        FWIW a GFCI is not required on the bathroom lights and fans, just the receptacles within 1m of the sink , shower and tub.
                        Good luck!
                        Jon

                        Comment


                        • #13
                          Interesting thread, I hope you find the problem and let us know what you find. I have a small generator and plan to power some circuits with a small manual transfer box with six circuits. I do have some ground faults spread throughout the house and would like to be sure things run smoothly if the need arises. With your bathroom using more than a few circuits I think that is maybe a better than worse scenario. My whirlpool tub uses two separate circuits and it is nice to have the lights stay on if the hairdryer trips the circuit it is on. I know many rooms in my house have a shared light circuit. That way you are not in the dark if you trip a vacuum or washer or some other thing like the cat chewing through a cord. Mike

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                          • #14
                            lost_cause, can you tell use the type/model of transfer switch fitted ?

                            Cheers

                            .

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                            • #15
                              Originally posted by Jon Heron View Post
                              FWIW a GFCI is not required on the bathroom lights and fans, just the receptacles within 1m of the sink , shower and tub.
                              the light in question is the ceiling light directly over the shower enclosure. i'm betting that it requires a gfci?

                              my initial guess that it was tied to the bedroom wiring was actually incorrect. i shut the breaker off and the light is not on that one. i'm pretty confident that gfci breaker is actually not for any purpose than the electrician didn't have any standard breakers left on him and didn't want to make another trip, so i got the gfci that he did have on him - the same approach that left me with one connection in the box with black tape and no wire nut.

                              Originally posted by Barrington View Post
                              lost_cause, can you tell use the type/model of transfer switch fitted ?
                              gentran 30310

                              now that i've done a little more looking and have done an internet diagnostic i'll wait till i have time to pull the covers off the panels to verify that there isn't already a switched neutral kit installed, and that my generator is still ground-neutral bonded. then i'll have the problem sorted fully.

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