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Thread: small cabin inverter/backup generator grounding

  1. #11

    Default Re: small cabin inverter/backup generator grounding

    Bryan,

    Are we talking about the same genset (Honda EU2000i)? I read the manual and the only thing I can find about this topic is the following:

    GROUND SYSTEM
    Honda portable generators have a system ground that connects generator frame components to the ground terminals in the AC output receptacles. The system ground is not connected to the AC neutral wire. If the generator is tested by a receptacle tester, it will not show the same ground circuit condition as for a home receptacle.

    I am not an electrician nor I want to make my life complicated, I just want advice making a safe electrical installation.

    Thanks.

  2. #12

    Default Re: small cabin inverter/backup generator grounding

    Off topic here, but did you by chance take an Advanced PV course online from SEI last spring? I think we were classmates.... either way good luck on your project.
    Saludos,
    HB

  3. #13
    Join Date
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    Default Re: small cabin inverter/backup generator grounding

    It is unfortunate the Samulex grounds the neutral... It would be better to just have the central Neutral/Ground bonding in your main power panel.

    I wonder if you can safety (and within warranty) disable the Samulex ground Bonding.

    In reality, with the small samulex wattage rating, I would not have a heart attack with Neutral/Ground bonding in the main panel and at the Samulex--You would get some shared current in the green and white wire--not the end of the world.

    But, it would not be an issue to leave the generator neutral floating either...

    In the end, neutral bonding at the Samulex and at the generator side of the transfer switch will meet your needs nicely and have consistent neutral bonding whether generator / inverter operation (and transfer switch will keep the "two neutral bond points" from interacting.

    As long as you use good AC wiring practices and components you are doing fine.

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  4. #14

    Default Re: small cabin inverter/backup generator grounding

    HB,

    That is me! I am glad you remembered.

    Thanks and good luck to you too.

  5. #15

    Default Re: small cabin inverter/backup generator grounding

    Bill,

    I thought about disabling the neutral to ground bond inside the Samlex inverter but I don't want to mess with warranty issues. Besides, as you mention, this is such a small system that it probably won't hurt to have the neutral to ground bond at the AC load center again.

    Thanks for your input.

    EB

  6. #16
    Join Date
    Jul 2007
    Location
    Quetico, Ontario
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    5,024

    Default Re: small cabin inverter/backup generator grounding

    Bill (or others)

    Can you explain, in simple terms the real world difference (s) between bonded neutral, floating neutrals etc in gennies as well as in inverter. I have a pretty good idea how bonded neutrals work, but I am a bit cloudier on floating neutrals. It might be a help for others.

    Tony
    Please note, being a moderator does not add any weight to my opinions 300 watts Siemens/BP panels,plus a Sun 90,, making ~400. ~30 amps into Rogue MPT-3024, 450 ah of Trojan T-105, Morningstar ts300 inverter, a Tri-Metric meter.a collection of antique generators, plus 2 Honda eu-1000i's (also a BS2512 IX controller) and assorted other stuff!

  7. #17
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    Florida, USA
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    Default Re: small cabin inverter/backup generator grounding

    The Honda generator needs to have neutral floating. Only the larger EU6500i, which is also a 240v/120v inverter/gen, can have neutral grounded.

    If you measure AC voltage at gen plug you will find about 60 vac from hot and neutral plug prongs to generator ground prong.

    Sounds like the Samulex only grounds neutral when transfer switch is on inverter output. This would allow you to keep the neutral floating on your house wiring when on Honda inv/gen.

    House breaker box needs to float the neutral bus bar.

    Other option would be to put an isolation transformer on generator. I would only do this if there is a utility grid connection which requires neutral grounded at breaker box/ service entrance by regulation code.
    Last edited by RCinFLA; January 18th, 2010 at 14:14 PST.

  8. Default Re: small cabin inverter/backup generator grounding

    re: "Are we talking about the same genset (Honda EU2000i)?" - yep.

    This topic has a lot of discussion on RV forums regarding this genset as that genset is very popular in those circles. The isolated power leads means that the little 3 light proper wiring indicators show fault when on the gensets and that confuses folks.

    One of the interesting points that comes up in this neutral to ground thing with the Honda 2000i is the difference between Canadian and US codes.

    The isolated power leads do mean that a high impedance voltmeter will show half voltage between either power lead and chassis ground. That voltage doesn't mean you can get any current. This is related to the 5kW boundary, though, as when power levels start to get past that the induced currents can be an issue in some circumstances.

    When I mention portable gensets with plugs and 5kW power levels, I am describing factors that are relevant to the code as I understand it.

  9. #19
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    Default Re: small cabin inverter/backup generator grounding

    Just think of a center tapped transformer. 120 VAC to center tap (A and B legs) and 240 VAC A to B legs.

    The maximum center-tap current is A to center-tap or B to center-tap loads. If you have a 10 Amp A-CT load and a 10 amp B-CT load--the Center-Tap actually carries near zero Amps.

    Notice, the only "short circuits" you can have are involve at least two of the three legs... A to earth, B to Earth, CT to earth shorts will involve no dangerous voltages or currents. A transformer (or un-earth genset/inverter) provides a "floating" output.

    So, the above is the relatively safe (Floating AC and DC circuits).

    Now, grounding the neutral/center-tap AC system... We are looking for protection of many types of failures. Say a 12,000 volt line crosses a 120/240 volt line. If the CT was floating, then the entire 120/240 volt home power lines would get energized to 12,000 volts and possibly not even blow a fuse anywhere (lots of fire and smoke in people's homes though).

    If the 120/240 lines are ground referenced, then a line cross will cause lots of smoke and sparks on the pole--but the homes will be relatively safe.

    And you can look at other floating vs ground referenced faults... For example, a floating 120/240 VAC circuit could have the A lead grounded (no current flow)--and now the B lead is now 240 VAC above ground (and the CT/Neutral is now 120 VAC with respect to ground). If the CT/Neutral was ground referenced, an A lead short to ground would pop the breaker and everything would remain at predictable voltages.

    Another reason for ground referenced neutrals was the way the old filament lamps are wired. The outside base of the lamp socket (which is easy to touch) is supposed to be connected to Neutral--(usually through a polarized two prong plug or hardwired lamp fixture).

    So--from my understanding of the history and goals of Neutral Grounding, that is why it is done that way here...

    In other countries they do things differently. In Germany, the wiring is not polarized (don't know which lead is hot/neutral--I don't even know if Germany grounds one of their 230 volt leads, or if they center-tap ground the 230 VAC transformer secondary at the pole/home).

    Modern stuff is now usually double insulated (two insulative/physical barriers) between the AC input and the DC output (like computer power supplies), plastic cases (which don't require the third wire grounding), etc.

    And even then, I have seen countries in the past (such as Iceland?) that did not allow double insulation but required a "ground screen" (tied to the green wire) between primary and output (such as on a computer power supply).

    Home generators do not have to worry about 12,000 volt mains crosses. And if 120 VAC, it does not matter much if a floating lead gets grounded... The other end is only still at 120 VAC above ground.

    Inverters, we have the MSW which are usually (by the way the design is implemented) referenced to the battery bank--and if the battery bank is grounded, the MSW inverter 120 VAC output is ground referenced too (but you cannot ground the "neutral" because the "reference" flips between plus/minus on the battery bank and will create a high amperage current path for battery current to ground through the inverter's internal FET/MOSFET switches.

    TSW inverter--again, like the genset, no high voltage lines to cross, floating output with respect to battery input, can usually ground reference the neutral.

    It is interesting (aka boring) and confusing.

    Anyway, I will stop here--before i dig myself deeper.

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  10. #20
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    Default Re: small cabin inverter/backup generator grounding

    By the way, the 60 VAC between A or B and ground is frequently just filter caps across the output to reduce electrical noise... Not much current (should be less than 5 mAmps of leakage).

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

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