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  • #16

    Re: small cabin inverter/backup generator grounding

    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!

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    • #17

      Re: small cabin inverter/backup generator grounding

      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, 14:14.

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      • #18

        Re: small cabin inverter/backup generator grounding

        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.

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        • #19

          Re: small cabin inverter/backup generator grounding

          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.

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          • #20

            Re: small cabin inverter/backup generator grounding

            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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            • #21

              Re: small cabin inverter/backup generator grounding

              Re: small cabin inverter/backup generator grounding

              Thanks Bill,, I THINK I got the gist of it. It explains why you can chose which leg to ground with the Suresine 300 inverter.

              I've got one more question for you. I have a series of buildings that are fed through a central "power house" In this shed are 2 stationary generators, 1 120 vac Onan the other a 240 Lister Diesel. These feed a central fuse box/distribution panel though a double pole triple throw switch. Also wired into this switch is a #12/2 wire with ground leading to a male plug. This allows me to feed the buildings with either of the older stationary gennies, or a newer smaller honda eu.

              The central fuse box is bonded to the frames of the two big gennies, and this box is in turn grounded to earth ground with ~#6 wire. (The genny frames are also bonded tot he same earth ground system.

              Now here is the question. When I plug the Honda Eu in and turn the 3 way switch, it energizes the buildings just fine. (Each of the "big gennies does as well) I also have a honda Ex series gennie that I can plug into that line and it works as well. The problem is if I plug in a 120 vac 2900wt Mitsubishi generator. As soon as I plug it in, it faults and trips its own out put breaker.

              The question is, if the Onan and the lister work fine with bonded neutrals, and the honda Eu works with a floating neutral, and the Ex honda works with what I assume to be a floating neutral, what do you suppose the deal is with the Mitsubishi?

              I am away from home for a month, so I can't confirm the details of that gennie, so I don't know how it is wired.

              Any ideas?

              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!

              Comment


              • #22

                Re: small cabin inverter/backup generator grounding

                Re: small cabin inverter/backup generator grounding

                My first guess is that there is a Black/White wire cross-over somewhere your wiring or Genset to common wiring connection.

                I would fire up the Mitsubishi and use a meter/load to see that the Neutral is really "neutral" with respect to the ground plug (and not hot).

                If I recall correctly this was a problem child you inherited (swapped out voltage regulator boards because of ground current problems?). Perhaps one or more of the Mitsubishi outlets have swapped their hots/neutrals (assuming it has a neutral to ground bond). When you plug into the building wiring, you end up with neutral bonding in two places (genset or genset wiring and main panel--and with the crossed 120 VAC leads, you end up with both power leads neutral/ground bonded).

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

                Comment


                • #23

                  Re: small cabin inverter/backup generator grounding

                  Re: small cabin inverter/backup generator grounding

                  Good idea, I will do that.

                  I am not sure how that might have happened as there would be no need to change any wiring to change the control board. And you are right, this is the gennie I got for $50. I use it to power the bigger saws, or to move around as a construction gennie. It is a great gennie now that we have solved the voltage regulator issue.

                  I'll repost the results later when I get home, and I shovel out the shed. I won't need this 'till sometime this summer.

                  Tonh
                  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!

                  Comment


                  • #24

                    Re: small cabin inverter/backup generator grounding

                    Re: small cabin inverter/backup generator grounding

                    Well Bill, you've done it again. Every time I start thinking that I understand this stuff a bit better, you make a post that does a pretty good job of reminding me that I don't. You and others here have such a wealth of knowledge, it's pretty much a daily reminder that there is always more to learn...
                    The more I learn the less I know,
                    HB
                    Off the grid, in the Sierra Nevada with 1200+/-watt "mongrel" PV array, 700AH surrette battery (ailing health), Outback MX60 charge control, VFX 3524 inverter, Generac 7.5kw generator, Honda eu2000 generator, also a Biolet dry composting toilet and small but growing organic garden... oh yeah and 2 GREAT dogs! Thanks for the forum

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