Outback Inverters/ X-240 Transformer Causing Generator Damage?

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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #32
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    Alan,

    I’ve reviewed this thread. In general, your system should work. We still need to confirm the actual inverter numbers. You can verify the model numbers from the label under the “manifold” cover and next to the battery posts. For example, my inverter’s label says it’s a 2024, which is correct for a model without the external cooling fan. However, mine has the fan, so it’s a 2524T.

    OutBack Series Stacking Operation (requires X-240 balancing transformer)

    With the "OutBack Series" stack and the X-240 transformer, the "master" inverter normally provides all power for 120 VAC loads on L1, 120 VAC loads on L2 (via the X-240), and all 240 VAC loads. The "slave" inverter sleeps in a very low power mode (~3 W, IIRC), and the green LED blinks to indicate this state.

    When the output of the "master" inverter increases to ~12 A AC (~1.4 kW), it will signal the "slave" inverter to turn on and help with the load. The "slave's" green LED will then illuminate continuously. I believe that each inverter should be supplying the same amount of power when they are both operating. Uneven loads on L1 and L2 are balanced via the X-240.

    Figures 6 and 7 in this X-240 manual may help explain this latter point: http://www.outbackpower.com/pdf/manuals/fw-x240.pdf

    When the total load on the two inverters drops back down to below ~4 A AC each (again, IIRC), the "master" will pick up the total AC load and signal the "slave" inverter to go back to sleep. The "slave's" green LED will than return to blink mode.

    You’ve already confirmed “OutBack Series” stack. Other settings to check include:

    Master Inverter: Plugged into Hub Port 1, and select Port 1 for relevant settings via the Mate
    Slave Inverter: Plugged into Hub Port 2, and select Port 2 for relevant settings via the Mate

    The FX Inverter/Charger Programming Manual may be a useful guide. See: http://www.outbackpower.com/pdf/manuals/fx_vfx.pdf

    Generator Specs and Related System Settings

    The AC2/Gen limit settings often need to be set much lower than the FX defaults. There are several reasons for this. One is that the generator’s real specs and conditions of use (altitude, temperature, etc) may result in considerably lower performance capability than the nameplate power spec may suggest. A related issue is that the generator’s breakers may not be able to sustain “rated” power output. Another reason is that the combination of pass-through loads and the inverters’ built-in chargers may exceed the generator’s capabilities. Yet another reason is that the FX inverters seem to pull a bit more current than the AAC setting would suggest.

    For example, this Onan “5500“ generator is rated at 4,000 W: http://www.cumminsonan.com/www/pdf/specsheets/a-1508.pdf

    Here’s a report I did on tests with my 2524T: http://www.outbackpower.com/forum/viewtopic.php?f=17&t=2134

    Based on the discussions above, you probably did the right thing insetting the AC2/Gen limit at 14 AAC for a “5500 W” generator. Assuming a real limit of ~16 A, that would mean a real load limit of ~1.9 kW on each leg. This limit does set the combined limit for AC throughput and charger current. As the downstream loads increase, the inverter will limit AC current to the battery charger to keep the total at ~14 AAC.

    In addition to setting these limits, you also need to tell the inverters to use this profile. Select “Gen” in the AC Transfer Control function.

    So, let me know how it’s going, and we can then get into additional specifics if required.

    HTH,
    Jim / crewzer
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  • AlanRT
    AlanRT Solar Expert Posts: 57 ✭✭✭✭
    #33
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    Hi Jim,

    Thanks for your very detailed reply. I know how much time it takes to think about and write up a reply like that and I truly appreciate the level of detail and trouble you went to.

    I'm up in Cal at the moment but my crew is returning this week to hook up the customer's new 17RES generator. I'll translate your advice into Spanish as best I can and send it to them to check.

    I'll also ask them to confirm the model numbers of the two inverters.

    Thanks Again,
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  • AlanRT
    AlanRT Solar Expert Posts: 57 ✭✭✭✭
    #34
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    I'm starting to think grounding could be an issue. The portable generators weren't grounded, and I'm assuming they should not be grounded. My understanding is that the inverters are the primary "utility" source so they should own the central grounding point for the entire electrical system, and that is where the neutral should be bonded to ground.

    But, in additional to the L1, L2 and neutral wires, we're going to install a safety ground wire and ground the generator frame to the inverter/gear ground bar. Then we'll take another look at the system to verify if there is a central ground point at the inverter, or if the system is also grounded or neutrals bonded to grounds at the load center.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,440 admin
    #35
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    Make sure that the grounding/neutral bonds/circuits are only tied to the DC grounding (negative assumed) is in one spot only. What you don't want is DC currents circulating through the AC neutral/ground system.

    Circulating ground currents in the AC lines/grounds have been accepted in utility installations (although--probably not good for lightning prone areas). For example, say you place your ground rod at the Inverter/AC bond. And run grounds/neutrals back to the genset, and run another ground rod into the earth at the genset... You will get AC current sharing between the Green and the Neutral wire (if neutral is bonded to earth at both the genset and the inverter/AC box).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • AlanRT
    AlanRT Solar Expert Posts: 57 ✭✭✭✭
    #36
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    OK, Thanks for that. We'll check the panel grounding and the load centers.

    These are all cement buildings here with embedded metal device boxes so at times it seems that everything is grounded everywhere. But frequently we come across load centers where all the ground wires are simply twisted together in a bundle and stuffed inside the load center with no connection to the neutrals or to a UFER ground point for that matter.
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
    #37
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    Hi
    Comments about grounding/grounded neutrals is really pertinent. I had problems with generator grounding recently. My large diesel 10kw genset had no problem running 240vac through an autotransformer down to 120vac, but a 5kw unit ran really squirrelly (my technical term). The T240 (Xantrex's version of X-240) had a neutral running back to the genset and it was conducting current through it returning to the genset windings. The result was imbalance between L1 and L2...sometimes L1 carried twice the current as L2. This led to very poor voltage regulation in the 5kw unit.

    To fix the problem I removed any 120vac loads from the 10kw genset and ran strictly 240vac loads (extra charger, water heater, T240)...and removed (floated) the neutral. There is no neutral conductor connected to the generator...

    The 5kw unit is 120/240 with duplex 120vac outlets on it's own panel. Without the neutral connected with the house/inverter ground point it has it's own grounding plate outside the garage...this keeps any 120 faulting from energizing the genset frame and zapping any operator. When running the T-240 now the 5kw unit is happy and will perform tolerably well.

    Ralph's rule of thumb...if you don't need a forklift to move your genset, it's too small. My `10kw Simpower must weigh over 1200 pounds, the 5kw Subaru about 200 pounds wet.

    Grounding conductor is the bare copper wire...Grounded conductor is the neutral (this took too long to clearly understand for me...grounding grounded shmounded!)

    Ralph
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #38
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    Alan,

    Always glad to help if/where I can. You might also want to check in with Kent Osterberg via the OutBack Forum (or via PM) re generator grounding.

    Best of luck!
    Jim / crewzer
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  • AlanRT
    AlanRT Solar Expert Posts: 57 ✭✭✭✭
    #39
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    OK, wanted to update this thread. The owner wasn't real sure what had happened to the last generator but now he says that the repair shop replaced a burned out voltage regulator. This leads me to further believe this is some kind of grounding problem, or problems with AC or DC current leaking back up the lines to the generator.

    We're just getting ready to install a new Kohler 17RES for this client and I sure want to solve this issue so it doesn't burn out the new gen. The generator pad will be about 15' from the inverters. I asked my guys to get me a complete picture of the entire system grounding today.

    I'm still reading through several posts on this forum and elsewhere to get a good grip on this to answer the following questions/assumptions. Your help appreciated:

    1. Does the Kohler 17RES have a floating ground?
    2. There should be no earth ground connection at the generator.
    3. In addition to L1, L2 and Neutral, we should run a 4th ground wire from the generator frame to the inverter frames?
    4. The generator neutral and ground should not be bonded to each other at the generator.
    5. The AC In/Out neutral and earth ground should be bonded to each other at the inverters?
    6. There should be a 4th earth ground wire installed between the main panel/load center and the inverters, and all circuit ground wires should be tied to this wire?
    7. The battery neg terminal and the inverter frames should be bonded to each other, and connected to the nearby ground rod.
    8. The primary (and only) earth ground point/ground rod in the entire system should be at/near the inverters.
    9. I'm assuming there is nothing we need to change about the auto transformer configuration that would have any effect on this issue.
    Many times the homes here are outfitted with a main service entrance and/or load center, and there may or may not be earth ground wires and/or bonded neutrals located there. If we find them there, I'm assuming we'll need to lift these in favor of #6 and #8 above. Remember. these are concrete buildings with metal device boxes, and the outlet ground wires probably all have an earth ground contact at each outlet.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,440 admin
    #40
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    Be a little "careful" about grounding statements...

    The generator frame should be grounded to earth ground. Whether that is a ground wire from the home, or a rod next to the genset does not matter too much (could even run both a common ground wire--at least as heavy as the AC leads from the genset or 6 awg -- which ever is larger and run ground stakes at both locations). What you don't want is your customer in muddy ground or touch a grounded metal water pipe/structure to and touch the housing of the genset and get shocked/electrocuted. (later on in this post, I will recommend that you run the safety ground from the generator frame backto the home safety/neutral bond for maximum safety).

    Think of the "ideal" grounding system as a start. The Ground Rod (or multiple Rods) are the center of the star. All grounds should run from their functional location back to the star. Your AC panel Neutral/ground should run back to the star. The Genset Frame Ground should run back to the center of the star.

    Your ONE DC Battery GROUND back to the Star (all other DC grounds should back to the battery "-" bus (like its own "sub-star").

    Try to avoid (for example) connecting a AC receptacle ground wire to a close by DC ground or a DC device with its safety ground tied to your "AC ground wire"... These mixing of AC / DC grounds can be an issue.

    That way, you will not have any mixed/circulating DC ground currents mixed with your AC power (which may have killed earlier generators).

    Regarding the Genset Neutral. If the generator Neutral is floating (with L1 and L2). When you connect it to the house power box--the neutral will be tied to earth/safety ground there. As long as this is a permanently wired connection--should be safe.

    If, you grounded the generator neutral at the generator frame and grounded the neutral at the home power box... Then you have a parallel path for AC power / Neutral current to flow. Either through the ground and/or through the safety ground wire that you run between the generator frame and the home ground connection.

    If you do this--run a separate ground wire from the home ground to generator frame ground--then the ground wire used needs to be at least the gauge as the neutral wire and able to handle all of the current (in case there is a short). In practice, the AC neutral current will be shared between the Neutral Wire and the Ground Wire (parallel paths).

    If I was doing the system (remember, this is "free internet advice" :roll: ) -- I would run a safety ground wire between the generator frame and the neutral/ground bond.

    The likelihood is small--but it is possible to energize the ground between a genset and the home (ground rod at generator, ground rod at home, no ground wire between gen/home). While a person may, or may not feel a shock when walking in wet ground (probably not likely in dry Mexico)--if there are cattle -- they can receive a fatal shock. Our legs-the current goes up one leg and down the other. A cow (or other livestock), the legs are much further apart and the current can go up the front legs, through the heart, and down the rear legs--and kill it.

    Granted--this is not a huge chance of this happening--but has been known to happen with high voltage transmission lines and their leakage current.

    Would also be a bit safer for people working on the setup (grounded electric tool plugged into the "home power', drilling/sanding/etc. on the generator frame).

    Running a safety ground wire between the generator frame ground and the home ground/neutral bond will help prevent any surprises.

    Sorry--long/wordy post... I did safety design on my equipment before--and it was these "weird" conditions that many times cause me the most problem when trying to design safe equipment.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • AlanRT
    AlanRT Solar Expert Posts: 57 ✭✭✭✭
    #41
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    To confirm, the single DC earth ground point and the single AC earth ground point should be separate earth ground points and not bonded to each other?

    BTW if it makes a difference, the generator will connect to the AC inputs on the Outback inverters through the Outback FlexWare AC panel. There is no direct connection between the generator and the house panel.

    I'm assuming the Inverters will sit more or less at the center of the star.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,440 admin
    #42
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    Regarding the AC to DC ground connections... One connection (typically at or near the ground rod) from both is what you will end up with (ground rod is center of star--in telcom, it was called the "ground window"). Once the AC or DC lead has left the center of the star, there should be no "jumpering" between the "rays" of the star (DC to AC especially).

    You don't want to "mix" your AC and DC grounds (such as run one ground wire around the home) and tie multiple AC and DC ground to it... That is where you can get DC current flow on your AC grounds and neutrals.

    For AC--typically, there is virtually zero current flow from the AC Hot/Neutral to the Ground (usually on the 0.001 amp or 1-5 milliamp level). AC power and safety grounds are isolated by design.

    With DC systems--typically the DC return back to the battery (for car/boat designed devices) have the "-" terminal to the case (for cars, the metal case is the return path to the battery). So--for many DC devices--the DC return and DC safety ground are one and the same. If you "tie" the DC equipment ground to your AC safety ground--you may then get current sharing between the DC return and the AC return--which then can get shared into the AC Neutral wire (for example, if the generator neutral is frame grounded and you use safety ground from generator back to the home safety/neutral bonding point).

    And given that DC currents tend to be 3-10 times as large for the same power levels (12-48 volt battery vs 120 VAC)--DC current impressed on an AC ground/neutral circuit can really cause problems.

    I am going to beg-off on answering on how to tie the Gen/Inverter neutrals and grounds. Other than to say "follow the installation manual and/or go to the Outback site and look at their wiring diagrams-off-grid systems"...

    I have never taken apart or looked in detail at an Outback Inverter--So, any thing I may try to add to the conversation regarding Outback would range from useless to wrong. :roll:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #43
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    Let's add a bit more confusion to the whole grounding discussion. :)

    If the resistance of a single grounding electrode (ground rod) exceeds 25 ohms, then the US National Electrical Code (Section 250.56) requires that a second grounding electrode be driven - with *at least* 6 feet between the two rods.

    I know you're in Baja and not subject to the USNEC, but I've run into this one several times in sandy soil (mountains and deserts), and I bet you've got sandy soil where you are.

    When I do it, I drive the two rods and connect them with a single unbroken wire; service -> water -> ground rod 1 -> ground rod 2.



    The first time I ran into this issue, was when I got called out to troubleshoot a service on a house that had had some sort of SERIOUS problem - serious enough to burn part of the neutral bus. I finally tracked it down to THREE serious problems all added up;

    1) There was no ground to water - someone had done some plumbing re-work and unhooked it and never hooked it back up.

    2) The lineman's crimp connection on the neutral from the pole drop wasn't tight and had overheated and burned up. You couldn't see that because it looked fine from the outside. When I went to check it though, it just came apart in my hand.

    3) The ground rod had been driven only 3 feet deep before they hit a rock - so they just sawed off the extra 5 feet.

    I ended up reconnecting the water ground, cutting off the lineman's crimp and using a split bolt, and yanking out the little 3' ground rod and driving a new one about 2' away - as well as installing a new service load center to replace the burnt one.

    The local inspector was a hotshot who measured the resistance of the ground rod and required me to stick in another rod. This was in a mountain area, and he said it was very common for the ground rod resistance to be excessive in the local (sandy and dry) soil.




    BTW, driving an 8' copper clad ground rod is a pain, and driving two is twice the pain - I usually rent one of these, which makes the job a piece of cake no matter how tough the soil:

    http://www.toolbarn.com/product/bosch/11304/

    Just take out the jackhammer bit and set the machine onto the end of the ground rod. The only problem is that the jackhammer is heavy and you have to heave it up a ladder to get it on the top of the rod, but after driving the rod a couple of feet it becomes very easy to handle.
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  • AlanRT
    AlanRT Solar Expert Posts: 57 ✭✭✭✭
    #44
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    Yes, soil conditions here are very sandy and dry. Customer is right behind the dunes 200' from the Pacific Ocean. Incredibly, 8' ground rods are difficult to come by here. Instead, 4's are common. I think grounding has not been a serious consideration in Mexico. Houses here in BCS are all concrete and rebar, yet UFER grounds aren't used.

    Although there is a Mexican electrical code, I have never seen a copy or any indication electricians here know anything about it. It's usually left up to the Architect to ensure best practices are enforced.
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  • AlanRT
    AlanRT Solar Expert Posts: 57 ✭✭✭✭
    #45
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    Also, to confirm, we won't run into problems by driving a ground rod next to the generator, connecting the generator frame to it, and running a ground wire from the generator frame to the Flexware panel ground bar, which is connected to the the other ground rod 20' away?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,440 admin
    #46
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    As long as the ground wire is the same gauge, or heavier, than the genset L1, L2, Neutral wiring (and the ground wire is rated to handle the generator's maximum output current--which ever results in a heavier gauge).

    You don't want to burn out the safety ground wire before any circuit breakers/fuses are tripped.

    The second ground rod at the generator may be redundant (belt and suspenders time)--but it certainly will not hurt and may protect against "weird" accidents/conditions (example: user disconnects the genset from the home and powers their RV/Trailer directly instead for some reason).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #47
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?
    AlanRT wrote: »
    I think grounding has not been a serious consideration in Mexico. Houses here in BCS are all concrete and rebar, yet UFER grounds aren't used.

    Ufer isn't really a very good ground anyway. Most places (in the U.S.) these days still require a ground rod (or two) even if you have a Ufer ground.

    In my example above, the problem was that when the lineman's crimp failed, the electricity flowed to ground...which had a *very* high resistance and burnt the neutral bus (which was bonded to ground in the service entrance).


    I've seen this high ground/neutral resistance problem manifest itself in other, truly SCARY ways as well.

    One (Ufer + rod grounded) building (in a high desert area in Nevada) had a very high resistance to ground, and an even higher resistance on the neutral. The incoming coax from the cable tv company was water grounded at the edge of the property (good water ground), so what happened was that the current flowing into the cable tv decoder box found a nice easy path to ground through the coax - which overheated the coax so that about 10' of it burned before it finally came apart and broke the connection.

    Another time (low desert area in California) I saw a situation (Ufer with no rod) where the cold water ground had a lower resistance than the neutral or the Ufer...but a higher resistance than the cast iron sewer pipe. So, when people touched a faucet *and* a drain at the same time, they got shocked. This happened if they were in the bathtub (with water in it) and touched the water faucet, or when they were touching the kitchen sink (stainless steel) and the faucet.


    You can get away with a crappy ground as long as the neutral on the grid connection doesn't have too high a resistance.


    As for that second ground rod being belt and suspenders...well, having an earth ground when you have a grid neutral is *already* a belt and suspenders situation - what's one more set of suspenders between friends? :D
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,440 admin
    #48
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    DHW,

    What is your recommendation? There is no Grid Power at the site (at least I think these are all off grid installations).

    "Grid Grounds" are "set" by the utility company driving a ground rod at their distributions transformers... At least that is what it appears to me. And then the Neutral is, again, bonded to the cold water pipes and a ground rod driven at the home (at least newer homes?)--again, as I understand.

    So--for the Off-Grid in Mexico--should there be driven grounds at both the home and genset -- or a rod at just the home, or just use Ufer grounding?

    And for those of us who have not heard of the "Ufer Ground"... A link.
    The term "Ufer" grounding is named after a consultant working for the US Army during World War II. The technique Mr. Ufer came up with was necessary because the site needing grounding had no underground water table and little rainfall. The desert site was a series of bomb storage vaults in the area of Flagstaff, Arizona.

    The principle of the Ufer ground is simple, it is very effective and inexpensive to install during new construction. The Ufer ground takes advantage of concrete’s properties to good advantage. Concrete absorbs moisture quickly and looses moisture very slowly. The mineral properties of concrete (lime and others) and their inherent pH means concrete has a supply of ions to conduct current. The soil around concrete becomes "doped" by the concrete, as a result, the pH of the soil rises and reduces what would normally be 1000 ohm meter soil conditions (hard to get a good ground). The moisture present, (concrete gives up moisture very slowly), in combination with the "doped" soil, make a good conductor for electrical energy or lightning currents.

    Ufer techniques are used in building footers, concrete floors, radio and television towers, tower guy wire anchors, light poles, etc. Copper wire does not function well as a "Ufer" ground due to the pH factor of concrete (+7pH is common). The use of steel reinforcement as a "Ufer" ground works well and concrete does not chip or flake as has been found with copper. The use of copper wire tied to the reinforcement rods outside the concrete shows none of these problems...
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #49
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?
    BB. wrote: »
    DHW,

    What is your recommendation? There is no Grid Power at the site (at least I think these are all off grid installations).

    "Grid Grounds" are "set" by the utility company driving a ground rod at their distributions transformers... At least that is what it appears to me. And then the Neutral is, again, bonded to the cold water pipes and a ground rod driven at the home (at least newer homes?)--again, as I understand.

    So--for the Off-Grid in Mexico--should there be driven grounds at both the home and genset -- or a rod at just the home, or just use Ufer grounding?

    And for those of us who have not heard of the "Ufer Ground"... A link.

    -Bill

    D'oh! I had replied to this, but I was in a hurry and I guess I didn't actually POST the thing... Ah well, it's for the best anyway since 5 minutes later while driving down the road I realized that I forgot to mention something important...

    So...here we go again. :)


    (I'm going to go by the NEC, even though I realize that Baja is not legally subject to the US NEC.)


    Since the house is not grid-connected, the generator (and the solar system) constitute a "separately derived system" (no permanent connection between building neutral and grid neutral), in which case a ground is *required*. I prefer a ground rod (or two) over a Ufer, so that's what I'd use (I would even if there WAS already a Ufer ground).


    Okay, first of all, I would make sure the house was properly wired - at least at the main load center. I.e., I would make sure that all the safety grounds were into a bus bar, and I would bond the neutral to the ground *at that point*.

    This is important, since the neutral to ground bonding should happen *at ONLY one point*.

    I would also make sure that in any sub-panels (and junction boxes and device boxes, etc.), the neutral and ground were NOT bonded.

    I also would NOT assume that there is any sort of acceptable ground just because the building is concrete.


    Then, I would drive a ground rod at the house (8' copper-clad 5/8"), and check the resistance. If the resistance is 25 ohms or less, then one ground rod would be sufficient.

    I will assume that the incoming water line is metal.

    Then, I would run a single unbroken *solid* copper wire of some stupidly large size - #4 at least, and maybe even #2. That wire would run *unbroken* like this:

    house panel -> water pipe -> ground rod -> generator frame

    If the resistance of the ground rod is more than 25 ohms, then we need a second ground rod, and since the two rods have to be at least 6' apart, I would drive the second rod at the generator for convenience. (Assuming that the gen is 6' away - most are.)

    In that case, the path of the unbroken solid wire would be:

    house panel -> water pipe -> ground rod 1 -> ground rod 2 -> gen frame


    Now, according to the Kohler 17RES installation manual:

    http://www.apelectric.com/v/vspfiles/pdf/kohler17res.installation.pdf

    "1.8.3 Grounding

    Ground the generator set. The grounding method must
    comply with NEC and local codes. Connect the
    grounding strap to the generator set ground lug,
    terminal GND inside the controller compartment.

    Kohler generator sets are shipped with the generator
    neutral attached to the generator in the junction box.    (emphasis added)

    At installation, the neutral can be grounded at the
    generator set or lifted from the ground stud and isolated
    if the installation requires an ungrounded neutral
    connection at the generator. The generator set will
    operate properly with the neutral either bonded to
    ground or isolated from ground at the generator.    (emphasis added)

    Various regulations and site configurations including the
    National Electrical Code (NEC), local codes, and the
    type of transfer switch used in the application determine
    the grounding of the neutral at the generator. NEC 2002
    Section 250.20 is one example that has a very good
    explanation of the neutral grounding requirements for
    generators."


    Okay, since the bonding of neutral to ground should only happen *at one place* (we're doing it at the house panel), and since the Kohler ships by default with the neutral bonded to the frame - I would unbond the neutral from the generator frame at the generator end. This way the neutral-ground bonding will happen ONLY at the main house load center - which is the proper place for it.



    Essentially, I would treat the building wiring as a separate system and make it proper unto itself - regardless of what the AC source is; grid, solar or generator.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,440 admin
    #50
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    Thank you Dwh,

    Very clear and well thought out--makes perfect sense.

    And you found the Genset Manual and its default neutral grounding.

    Well Done! :D
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • AlanRT
    AlanRT Solar Expert Posts: 57 ✭✭✭✭
    #51
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    Hello All,

    I've been remiss in following up. Thank you all for all the great information, especially DWH's step by step analysis. You did a lot of footwork to pull that together.

    We followed these steps and so far have had no problems with the new gen set blowing out.

    I should add that rural Baja does not use metal water piping, at least not the main supply outside the building. It's all plastic here. They do use copper supply piping embedded in the concrete walls and slabs of the buildings themselves.
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #52
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    Re: Outback Inverters/ X-240 Transformer Causing Generator Damage?

    Has there been a analysis on how the generator failed?

    Is it absolutely necessary to have the load balancing transformer on output? Only reason would be if one leg is exceeding capability of Outback inverter. This situation would likely be pump running (assume it's 240v pump) and 120v loads to house add to more then single Outback can handle.

    Most transformers have slightly more then a 1:1 transformation (like 1:1.03) to make up for transformer loss in a step down or step up configuration.

    My first inclination is to suspect backwash current on one leg into generator for long period of time. I am not real familar with Outback alarms, does it have one that trips for 'AC out connected to AC in' which would be case if transformer was pushing power backwards from one side to other when voltages mismatched due to different L1 to neutral and L2 to neutral loads.

    A lot of newer generators have electronic regulators that regulate field current based on current sense on their L1 & L2 legs , along with output voltage. They don't know power flow polarity because they assume it's an output load so an input forced current would signal regulator to turn up the field current.

    All syncronous grid tie hybrid inverters have some backwash but usually for only a short period of time (unless in sell mode). This is caused by fluxuations in loads on L1-neutral and L2-neutral resulting in voltage fluxuations that take a short time for the inverter to readjust its matching voltage. I always worried about this but only in case where an inverter-generator was used.

    Isn't the maximum ACin to ACout current pass on Outback 60 amps? If so would seem safer to do the generator load balance on the AC input side. If the customer is already running the gen during pumping then he probably doesn't need the Outback output side balancing for the case of a battery supply only pumping and house load situation.
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