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lost_cause
12-30-2013, 08:55 PM
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.

lakeside53
12-30-2013, 09:12 PM
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.

darryl
12-30-2013, 09:21 PM
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.

lakeside53
12-30-2013, 09:32 PM
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.

lost_cause
12-30-2013, 09:39 PM
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.

KJ1I
12-30-2013, 09:50 PM
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.

J Tiers
12-30-2013, 10:01 PM
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".

Barrington
12-31-2013, 09:11 AM
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

.

vincemulhollon
12-31-2013, 09:13 AM
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!

Jon Heron
12-31-2013, 09:41 AM
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

lost_cause
12-31-2013, 01:15 PM
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.

Jon Heron
12-31-2013, 02:51 PM
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

Mike279
12-31-2013, 02:52 PM
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

Barrington
12-31-2013, 03:03 PM
lost_cause, can you tell use the type/model of transfer switch fitted ?

Cheers

.

lost_cause
12-31-2013, 03:37 PM
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.


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 :D 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.

KJ1I
12-31-2013, 04:15 PM
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.

Are you sure its a ground fault breaker and not an arc fault breaker?

Barrington
12-31-2013, 04:27 PM
gentran 30310
A quick look at the installation instructions( http://www.gen-tran.com/assets/pdfs/vintageInstall.pdf )
confirms what I first thought, so I can only repeat:-


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.

The gentran units are indeed wired between the output of the original circuit breakers and the circuits themselves, switching just the live connections, resulting the effect described above.

I can't however see any simple way of getting around the problem, apart from abandoning the GFI.

I also repeat that the GFI is providing NO protection when under generator power.

Cheers

.

lost_cause
12-31-2013, 04:49 PM
Are you sure its a ground fault breaker and not an arc fault breaker?

i'm feeling not-so-smart right now... i was totally unacquainted with the concept of an afc fault breaker. knowing the date of installation, i'm going to guess that's what it is then... the two breakers that look the same in the box - the one labeled "whirlpool tub" and the one labeled "master bedroom" look the same from what I can see that is exposed, and there are no markings on them that i can see to indicate what they are. i assumed gfci, and it looks like i'm probably wrong in one case.

i've also found that my generator is actually a floating neutral, so my assumptions are totally wrong so far... i'm not familiar with what makes an arc fault breaker tick, or trip in this case, so i'm open to suggestions again... could be a super-sensitive breaker, or are these likely to act this way with generator-line switching?

Barrington
12-31-2013, 05:00 PM
OK, one last try...

This is what's happening with the circuit switched to generator and no utility power (thicker lines show current flow):-

http://i564.photobucket.com/albums/ss82/MrBarrington/GFI_zpsecf51466.jpg

All the circuit current is passing through the neutral path of the GFI, but it doesn't trip because it has no line-neutral voltage to power its internal circuit.

In this condition, restoring the utility power powers up the GFI and it responds to the imbalance by tripping.

Cheers

.

lost_cause
12-31-2013, 05:03 PM
A quick look at the installation instructions( http://www.gen-tran.com/assets/pdfs/vintageInstall.pdf )
confirms what I first thought, so I can only repeat:-



The gentran units are indeed wired between the output of the original circuit breakers and the circuits themselves, switching just the live connections, resulting the effect described above.

I can't however see any simple way of getting around the problem, apart from abandoning the GFI.

I also repeat that the GFI is providing NO protection when under generator power.

Cheers

.

you bring up a point that i had never really considered either... i worked under the assumption that since the work was done by a qualified person, that all is well. at the date of the original transfer switch installation i don't think there would have been any gfci protected circuits anywhere in the house, so everything was probably fine. now, after a little bit of renovating, things are different. maybe there is no solution, but the ever changing codes dictate the hoops we have to jump through, and in the end, it may be a waste of time. sure, the circuits are powered by generator a very small percentage of the time, but those are the time when catastrophe is likely to happen - a big tree crashing through the house wiring, water infiltrating the house and going where it shouldn't - those are far more likely when you are in the adverse conditions that would require a generator.

here's a thought - instead of a gfci breaker, what about a gfci receptacle on a normal breaker as the first thing in the circuit, eliminating the gfci breaker completely, but keeping the gfci device in the circuit when under generator power. are there any cases where this is not acceptable and you need a gfci breaker?

of course, none of this solves the issue of the afci breaker which my lack of knowledge didn't pick up on.

lakeside53
12-31-2013, 05:25 PM
GFCI outlets are fine so long as they do not have common neutrals to other circuits in the downstream wiring. The old method of "twist all the whites together in the box" doesn't work.

edit - replaced upstream with downstream! not driving tonight...

J Tiers
12-31-2013, 07:37 PM
If, as might be the case with some statements above, the offending item is actually an arc-protective breaker, it is possible that noise from genset brushes (if it has any) may be triggering it. They can produce a signal which looks like the signal from an arc. The breaker wouldn't be powered until grid power is restored.

The bedroom breakers are, under new codes, required to use the arc-protective breakers. You mentioned they were to bedrooms, I think.


GFCI outlets are fine so long as they do not have common neutrals to other circuits in the upstream wiring. The old method of "twist all the whites together in the box" doesn't work.

Not certain what you mean here, but the GFI (GFCI) will be fine protecting it's own outlet, and any correctly connected downstream outlets virtually regardless of any upstream connections. It only cares about the balance of current going through it.

kf2qd
12-31-2013, 08:21 PM
Possible ground currents showing up because of an out of phase condition between the generator and the power company. Possibly a very small current that is induced because of the out of phase condition between the 2 sources..

lakeside53
12-31-2013, 09:15 PM
it's New Year's eve and I've had couple but I'll try to explain :)

The key is (as you say) is "correctly connected down steam". I've had to figure out why many retrofit homeowner gfci installations didn't work. Mostly there were down steam neutrals from other circuits connected to the gfci "neutral". Lights and receptacles in the bathroom or garage on different circuits having a common box often led to this.

In the case of the OP, this probably won't apply as his breaker has been working fine.

garyhlucas
01-02-2014, 08:25 PM
A little more about GFCIs. They make big ones too, they are required on services rated at 480 volts or more and 1000 amps. The trip setting on those is about 200 amps. It is not intended to protect people. It is intended to stop a high resistance ground fault which could consume say 800 amps at 480 volts without ever tripping the main breaker. Imagine the arc and heat that would produce! I had a couple of guys working with me that barely got out of an electrical room alive when the main service just melted down on a job.

The interesting part is that you don't directly look for some kind of load difference on the hot and neutral, it is much easier than that. You just run the hot and neutral both through the same current sensing loop. If what goes out on the hot is the same as what comes back on the neutral the sum of the power sensed is zero. So any current flow in you sensing loop is due to a ground fault, power is going some place else. This of course is why it trips with the generator, some power is going somewhere else. A ground fault sensor needs to be downstream of the transfer switch to work properly. I don't like GFCI breakers, they too often nuisance trip, and no one tests them. One at my daughters house powered a receptacle in the hall way, and oh yeah, an outdoor receptacle that filled with water every time it rained! Better to have GFCI receptacles at each point of use where they are needed. Then you will be aware of what tripped it, and right there to reset it.

Noitoen
01-03-2014, 07:05 AM
I live in Europe and here, we have 3 phase and neutral supply. In the factories, our step down transformers 15Kv or 30Kv are delta/star configuration and the secondary's star connection is connected to a ground bar array, separated from the ground protection array, so, this leaves us with 5 conductors. 3 phase lines, a neutral line and a earth line. Usually the main circuit breaker does not have ground fault protection as this would be a nuisance every time there was a problem with some secondary circuit, it would trip the all the power. The various separate circuits receive each a adjustable ground fault protection relay in which the time to trip and leakage current can be adjusted (usually 1000mS 10A at my plant). This cares for direct ground fault and ignores electronic filter noise in VFD's and SMPSU's. To protect people, we use 300mA, 30mA and 3mA GFCI's in various locations.
When we use backup generators, for the systems to work properly, the generator's star/neutral connection must be grounded at the generator side and the switch over connector must cut the 4 supply lines otherwise you get problems with neutral loops.

At home, I have a 3phase and neutral supply and derive to various small switch boards.The kitchen garage and shop get 3phase. The other 2 floors get single phase each with a 30mA GFCI's. The independent protection circuit breakers are DPn which cuts phase and neutral. This helps troubleshoot any problem such as a wet receptacles.