Trying to charge off-grid set up from generator -- blowing GFCI breakers?

PorkChopsMmm · October 2012

I've discussed this briefly in the off-grid forum but wanted to bring this to the larger forum for input.

Background:
I have a 100% offgrid setup with an Outback inverter, charge controller, battery monitor, etc. etc. powering my house and the solar components are all mutually grounded to a single 8ft copper rod pounded into the ground. I recently moved my power shed, trenched a long AC run, and relocated all of my solar equipment. A new 8ft copper rod was driven at the new power shed site. Symptoms did not change. Things only got worse tonight when I installed a high amp rated 4 prong 120/240 twist lock receptacle and a 120 Volt normal receptacle (I only used the 120V receptacle -- I don't have a twist lock cord yet). After this change I could not the generator to run without constantly popping the breaker. I double checked all of the grounding -- it was good before the power shed move and is good now.

Problem
I have a large construction generator, an Ingersoll Rand G7HE 7KW 50 Amp generator. It has 2 GFCI 120V outlets that have their own breakers separate from the "reset" and "test" buttons on the outlet itself. Whenever I try and charge my battery bank the generator every few minutes OR under a large load (e.g. running water pump and charging battery bank -- max output from the generator is 2KW) the breakers pop. This is driving me crazy! I was able to do some jerry-rigging listed below with varying levels of success. At best I could charge the battery bank and if a large load came on the breaker would pop and reset (because it was taped down) after 30 seconds or so. So every few minutes the breaker pops and the inverter stops charging the batteries for 30 seconds or so. It is a very inefficient way to try and charge my bank.

Additional Info
This generator works beautifully when running hand tools, air compressors, etc. Anything I can throw at it. It is only when I have it try to charge the battery bank that breakers pop. Also, I have used a smaller non-GFCI generator to charge the battery bank. It works like a champ and has never given me a problem.

Things I have done to try and stop the breakers from popping:
- Disconnected the common ground from the frame of the generator
- Tied the generator into the ground for the solar system
These last 3 worked the best...
- Used an extension cord with the ground removed
- Taped down the "breaker" for the outlet since under some circumstances it blows (a circular "breaker" button above the GFCI outlet)
- Lowered the amperage being used by the inverter to power the batteries. This worked well enough but my 7KW generator, when running at full-tilt, was only providing 700 watts or so.

Questions
Any advice on how to proceed? I want this to be a well designed set up and taping down breakers and removing grounding pins from cords is not a good solution. My hopes tonight were that by tying the generator into the grounding rod that the solar setup was using and wiring a dedicated outlet with 10/2 wire would give me the infrastructure to charge the bank. I am no where near the 20 Amp limit of the receptacle -- we are talking 6 amps as set in my inverter charger configuration screen.

Any tips or suggestions would be appreciated. Thanks!

ChrisOlson · October 2012

Re: Trying to charge off-grid set up from generator -- blowing GFCI breakers?

While the grounding may be good, the GFCI trips because it sees a ground fault. GFCI's work by measuring the current through the hot and the neutral, and trip if they aren't equal.

Where is your system neutral/ground bond made? Generators with GFCI have the generator frame hooked to neutral, otherwise the GFCI wouldn't work because there would be no alternate path to ground. So if you have the required neutral/ground bond made at your service panel or inverter, now you got two neutral/ground bonds (because of the GFCI generator), and you can't have that.

So where is your system neutral bonded to ground besides the generator?
--
Chris

PorkChopsMmm · October 2012

Re: Trying to charge off-grid set up from generator -- blowing GFCI breakers?

I have a bus bar that I connect the charge controller, inverter, and breaker panel to. This bus bar is then grounded to the grounding rod outside. Tomorrow morning I am going to go and remove the grounding wire from the generator that goes to the grounding rod and see if that makes a difference.

ChrisOlson · October 2012

Re: Trying to charge off-grid set up from generator -- blowing GFCI breakers?

Your battery bank ground should also be hooked to that ground rod so there is no potential between the AC system grounds and DC grounds. But that's a separate issue.

Your electrical system must have the inverter neutral bonded to ground at one point, and only one point, in the system. At all other places in the system (subpanels, etc.) neutral and ground are kept separate. Power flows in the neutral during normal operation - it never flows in the ground unless there's a fault. The GFCI is detecting > 10 mA difference between hot and neutral, and that's why it trips. The reason it's detecting a difference is because you have "leak" someplace where power in either the neutral or hot is flowing to ground.

If you have two neutral ground bonds in the system you create a ground fault loop where neutral has more than one path to ground. This is VERY dangerous and will kill you if you use an appliance or tool that develops a ground fault.

Before you do anything further, please check the following: disconnect your generator from the inverter. With an ohm meter check a standard 120 volt outlet in your home by putting one probe lead into the ground of the outlet and the other into the neutral (the neutral is the larger of the two blade holes). The ohm meter should show 0.0-0.1 ohm. If the ohm meter shows open (no grounded neutral), or higher resistance than 0.1 ohm, I would highly suggest getting a licensed electrician out there to fix it before somebody gets electrocuted.
--
Chris

PorkChopsMmm · October 2012

Re: Trying to charge off-grid set up from generator -- blowing GFCI breakers?

ChrisOlson wrote: »

Your battery bank ground should also be hooked to that ground rod so there is no potential between the AC system grounds and DC grounds. But that's a separate issue.

That's interesting. Never heard that suggested. How do you ground the battery bank?

ChrisOlson wrote: »

Before you do anything further, please check the following: disconnect your generator from the inverter. With an ohm meter check a standard 120 volt outlet in your home by putting one probe lead into the ground of the outlet and the other into the neutral (the neutral is the larger of the two blade holes). The ohm meter should show 0.0-0.1 ohm. If the ohm meter shows open (no grounded neutral), or higher resistance than 0.1 ohm, I would highly suggest getting a licensed electrician out there to fix it before somebody gets electrocuted.

Thank you for the advice -- I will check it tonight. I did disconnect the generator from the grounding rod this morning and I had the same popping of the breakers the instant I plugged the cord in. The only thing that worked previous to this was removing the ground pin from the extension cord hard wired into the inverter. When I hard wired the inverter into the new receptacle I hooked up the ground. I guess another test would be disconnecting the ground in the receptacle and seeing if that changes anything.
--
Chris[/QUOTE]

ChrisOlson · October 2012

Re: Trying to charge off-grid set up from generator -- blowing GFCI breakers?

You want zero potential (voltage difference) between grounds in your system. Otherwise you could get a shock by touching two different grounds if one is carrying power because of a fault and the other isn't. The DC ground is bonded to the AC ground at the grounding point, typically by running a 6 AWG grounding wire from the negative DC bus bar to the ground rod and secured with a separate clamp. This is required by NEC, although I'd have to look up the appropriate section to get the exact wording.

I'm worried that your system either doesn't have a neutral/ground bond on the AC side (or you have more than one), and that is a very serious issue. Without the bond the only path to ground is thru you in the event of a fault and that can result in death. If you have more than one you create a ground fault loop with the ground carrying return power instead of the neutral because it puts the ground in parallel with the neutral wire.

Typically the generator should have a floating neutral when used with an off-grid inverter system. The Outback inverter does not have an internal neutral/ground bond, so neutral is bonded to ground at the service panel. When you hook up a generator with a floating neutral the generator frame is automatically grounded thru the grounding conductor (ground pin that you removed) in the cord.

You have a GFCI generator so it has a bonded neutral, meaning the generator neutral is connected to the generator frame.

Again, I can't stress enough that if you don't understand this, please just hire a licensed electrician to come and fix it. His fees will be way cheaper than somebody ending up dead because of a system that's not wired to code.
--
Chris

BB. · October 2012

Re: Trying to charge off-grid set up from generator -- blowing GFCI breakers?

Just to be very clear--Your system is tripping the GFI breaker, not the over current side of the breaker?

The usual issue is that larger genset (over ~3.5 kW?) tie their neutral to the frame ground at the generator. And if AC neutral is tied to earth ground at the main panel, you will have current flow it both the neutral and earth ground leads from the generator (the neutral and earth are in "parallel" and both carry some of the current).

Lifting the ground in the extension cord is one way of addressing the issue. Lifting the neutral to frame ground inside the generator is another.

When hardwiring the system... Lifting the earth/neutral connection in the generator (and bonding the earth/neutral in the main panel), plus carrying a green wire from the genset to the main panel earth/safety ground bond should be the answer.

detaching the safety ground (green) wire from the generator leaves you with a dangerous situation... It is possible (say failing/intermittent neutral wire connection from main panel to genset) to cause the metal frame of the generator to become energized with 120 (or 240) VAC. Obviously, a vary dangerous situation.

Sorry to be so repetitive with my post (after Chris' posts)--But I want to make sure that you safely address the situation. You may even need to find an electrician that works with genset installations to find one that really understands the issues (I am not sure that all electricians will).

In other installations (such as an RV), they have the issue that a grounded neutral is supplies from the RV park plug. And then need to supply an earth/frame bond when using an on-board generator. The usual way of addressing the problem is to use an AC Transfer Switch that not not only switches the "hot leads" but switches the Neutral Leads too... This allows the RV park to supply a grounded neutral when on park power, and the local genset to supply frame bonded neutral when on generator power.

-Bill

PorkChopsMmm · October 2012

Re: Trying to charge off-grid set up from generator -- blowing GFCI breakers?

Thanks guys. I will give a local electrician friend a ring and see what he thinks. I will also test the voltage of ground when I get home.

PorkChopsMmm · October 2012

Re: Trying to charge off-grid set up from generator -- blowing GFCI breakers?

Talked to my electrician buddy -- he is ~65 years old and a semi-retired master electrician. He knew exactly what you all were saying but didn't think it was a deadly scenario. He also suggested I test the outlets (neutral to ground with a voltmeter) to see if there is current. I did test and saw that some outlets, I didn't test all, had current. It seemed to fluctuate between .7V and 1V.

My plan now is to turn off all breakers in the house, turn on one breaker at a time, and check outlets on that run to see if there is a suspect outlet on that run that is causing the problem. If I can narrow it down to one breaker and the outlets/fixtures on that breaker then I will take all of the covers off and check my wiring.

Is there any other way to test? Will an outlet with a crossed or touching wire give off my current on neutral to ground than others? If so, that would be a helpful way to test.

Thanks!

inetdog · October 2012

Re: Trying to charge off-grid set up from generator -- blowing GFCI breakers?

PorkChopsMmm wrote: »

Talked to my electrician buddy -- he is ~65 years old and a semi-retired master electrician. He knew exactly what you all were saying but didn't think it was a deadly scenario. He also suggested I test the outlets (neutral to ground with a voltmeter) to see if there is current. I did test and saw that some outlets, I didn't test all, had current. It seemed to fluctuate between .7V and 1V.

My plan now is to turn off all breakers in the house, turn on one breaker at a time, and check outlets on that run to see if there is a suspect outlet on that run that is causing the problem. If I can narrow it down to one breaker and the outlets/fixtures on that breaker then I will take all of the covers off and check my wiring.

Is there any other way to test? Will an outlet with a crossed or touching wire give off my current on neutral to ground than others? If so, that would be a helpful way to test.

Thanks!

A voltage difference between the neutral and the ground wire at an outlet is not unusual, it just means that there is something plugged into that circuit which is drawing current and causing a voltate drop between the neutral and the panel. The ground wire should not be carrying any current under normal use, so its voltage should be exactly the same as the ground wire at the panel.

Your problem seems to be that the ground and the neutral are connected together somewhere other than at the panel, so that some of the current which should be returning via the neutral is instead going back through the ground wire. If that is the case, then the outlet nearest to where the cross connection is happening would measure zero volts between neutral and ground.
Unfortunately, you will also measure zero volts between neutral and ground if there are no loads turned on for that circuit, so it is not a definitive test.

You could try plugging a toaster or other high current appliance into each outlet in turn. If you find one were the ground-to-neutral voltage stays at zero (or does not change at all) when the toaster is turned on, then you are close to the problem area.

RCinFLA · October 2012

Re: Trying to charge off-grid set up from generator -- blowing GFCI breakers?

I noticed your generator has a 120v/240v switch to allow full power at 120 vac. Usually when there is a 120v/240v switch the neutral is not connected to frame at chassis. When you have the switch on 120v only, then one of the 240 v hot prongs on the 120v/240v twist socket is likely also connected to neutral. Only one of the L1/L2 lines are live with the 120 vac. Since it is a 30 amp socket you cannot get full 7 kW out of the 30 amp outlet, only 30 amps.

It appears with the outlets shown in the picture, the only way to get full gen power at 120 vac is to use multiple socket outputs which is a no-no unless they are separate appliances. Don't try to wire multiple plug outlets to a single feed to your house. That would be what is called a 'suicide cord' setup with multiple hot male plugs. The current would likely not be properly shared between outlets causing a cascade tripping of each outlets respective breaker.

If your house wiring has a ground bond at the breaker panel, the best way to run is to use 4 wire cord to bring the generator ground prong (chassis ground) independently back to the ground in the breaker box. The neutral should not be connected to ground at generator. Do not separately ground generator chassis. As long as you only use the single plug in cord and its ground is connected at breaker box it will be a safe setup.

By tieing the neutral to ground at box and at generator you have the current carried in the return potentially shared between the ground wire and neutral wire to generator which will trip the generator GFI. A GFI only needs 20-50 uA (that's micro-amps) imbalance between hot and neutral current to trip it. You can have 30 amps carried on the hot wire and 30 amps minus 50 uA carried on return neutral and the GFI will pop.

ChrisOlson · October 2012

Re: Trying to charge off-grid set up from generator -- blowing GFCI breakers?

When used as a stand-alone power source (a “Separately Derived System” in NEC parlance), OSHA requires that portable generators have a bonded neutral and GFCI protection with floating ground. Refer to:
29 CFR 1926.404 (f)(3)(iii) "Neutral Conductor Bonding":
A neutral conductor shall be bonded to the generator frame if the generator is a component of a separately derived system

The NEC reference to this is Article 250.34(C). There used to be a GFCI exemption on generators smaller than 5 kW, two-wire single phase. That was eliminated in NEC 2002, and ever since then AHJ's will require the use of GFCI's on portable generators on construction sites. There is no way the GFCI can work without a bonded neutral on a dual voltage system. Without the neutral bond, electricity will not leak to the equipment grounding conductor to trip the GFCI - it's only path is thru the human using it (assuming a hand tool on a construction site) to ground and back to the generator, leaving a dead human which is highly frowned upon on construction sites.

This is why two-wire single voltage generators with floating neutral do not require GFCI - you can come in contact with either conductor and won't get a shock because there is no return path thru you to the generator. In order to have a true neutral you need to center tap the winding, meaning you have a dual voltage system.

This generator in question has a bonded neutral. All that 120/240 switch does is reverse the polarity of one coil group by connecting either the start lead of the coil to neutral or the end lead. In one configuration the coil group generates a sine wave that is in phase with the other coil group (parallel configuration - 120V only). In the other it generates a sine wave that is 180° out of phase with the other coil group (series configuration - 120/240 with neutral as reference).
--
Chris

inetdog · October 2012

Re: Trying to charge off-grid set up from generator -- blowing GFCI breakers?

ChrisOlson wrote: »

When used as a stand-alone power source (a “Separately Derived System” in NEC parlance), OSHA requires that portable generators have a bonded neutral and GFCI protection with floating ground. Refer to:
29 CFR 1926.404 (f)(3)(iii) "Neutral Conductor Bonding":
A neutral conductor shall be bonded to the generator frame if the generator is a component of a separately derived system

The NEC reference to this is Article 250.34(C). There used to be a GFCI exemption on generators smaller than 5 kW, two-wire single phase. That was eliminated in NEC 2002, and ever since then AHJ's will require the use of GFCI's on portable generators on construction sites. There is no way the GFCI can work without a bonded neutral on a dual voltage system. Without the neutral bond, electricity will not leak to the equipment grounding conductor to trip the GFCI - it's only path is thru the human using it (assuming a hand tool on a construction site) to ground and back to the generator, leaving a dead human which is highly frowned upon on construction sites.

This is why two-wire single voltage generators with floating neutral do not require GFCI - you can come in contact with either conductor and won't get a shock because there is no return path thru you to the generator. In order to have a true neutral you need to center tap the winding, meaning you have a dual voltage system.

This generator in question has a bonded neutral. All that 120/240 switch does is reverse the polarity of one coil group by connecting either the start lead of the coil to neutral or the end lead. In one configuration the coil group generates a sine wave that is in phase with the other coil group (parallel configuration - 120V only). In the other it generates a sine wave that is 180° out of phase with the other coil group (series configuration - 120/240 with neutral as reference).
--
Chris

I think you are misinterpreting the way a GFCI works, Chris.
It does not rely on current flowing through the grounding conductor (or anywhere else specifically). What it detects is that the current in the hot lead is not equal to the current in the corresponding neutral lead.
As a result, if there is current leakage in the load equipment (in the worst case, through the operator), then no current will flow through the operator to ground unless the neutral and ground are bonded somewhere. But if current somehow flows through the operator back to the neutral wire, then the GFCI will not be able to detect that and will not trip.

The issue here is that since the current NEC requires a bonded neutral at the generator, the neutral must not also be bonded to ground at the load center or elsewhere in the circuit. A separately derived system must have its (grounded) neutral bonded to the earth ground system at exactly one place. The same applies to the POCO connection, except that if a transformer supplies multiple services there must still be a neutral to ground bond at each service. (This can cause very strange behavior in cases where a neutral conductor is accidentally interrupted and the "normal" load current ends up flowing through the earth from one house to the next to complete the circuit.)

ChrisOlson · October 2012

Re: Trying to charge off-grid set up from generator -- blowing GFCI breakers?

No, I understand how the GFCI works. The purpose of the bond is to provide a path (besides thru a human) to ground in the event a current imbalance exists between the hot and neutral conductors. The neutral must be bonded to ground at the service entrance or load center. So in order to use a GFCI generator as a standby power source for a home the neutral ground bond at the generator must be defeated.

That's why I recommended in the first place to get an electrician (that understands genset installations) out there to fix it. There is obviously current flowing in the ground in this case, which means something is not hooked up right. Grounding everything is one issue, but that bond between the neutral and ground is another.

I worked on genset installations for 19 years for Cumminc Power Generation - mostly megawatt class units. But the only difference between a one megawatt generator and a 1 kW generator is the size, and big units are three-phase.

Edit:
Adding some more comments:
GFCI does not prevent electric shock. It shortens the time that the hazard exists to make it more survivable. Secondly, you do not necessarily have to defeat the generator's neutral/ground bonding IF you use transfer gear with a switched neutral. However, in this case, the Outback inverter does not have that. It uses pass-thru neutral.

The GFCI did it's job here in indicating that there is a problem someplace. I really think this is one that an electrician should look at and not provide information on an internet forum on how to "fix" it - because none of us can see how the system is wired up and if the information is wrong somebody could end up getting a shock. An electrician that is familiar with genset installations will see the problem within a few minutes, and his fees will be cheaper that doing things like removing the ground pin from the cord to try to "fix" it - and possibly somebody gets a wild hairdo by touching the generator.
--
Chris

Trying to charge off-grid set up from generator -- blowing GFCI breakers?

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