Announcement

Collapse
No announcement yet.

transformer inverter vs. transformerless inverter - worth the savings?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #31
    Originally posted by inetdog View Post
    What MH is saying is that if there is a local ground rod driven which is physically (and therefore electrically in terms of induced voltage in local earth from enormous lightning currents) distant from the main ground electrode grid it must be connected via a GEC (wire or structural steel or other excellent conductor) back to the primary GES of the building. Just connecting the panel frames, racking, and array end electrical wiring enclosures to an isolated local electrode, with only an EGC to bond them back to the main building bond grid, will cause high currents to flow in that EGC with equally high offset voltages that can destroy electronics and/or start fires.
    It is easier to simply avoid the local earth electrode in the first place.

    And if I have misstated anything above, I am sure Sunking will correct me.
    NO. he said ONE earth ground. period. not 2 or 3 or 'n' grounds. you can have spurious voltage flow from ground rod to ground rod via the path between them in the event of a lightning strike which can then destroy electronics and/or start fires or worse.

    Comment


    • #32
      Originally posted by Jest Waitn View Post

      NO. he said ONE earth ground. period. not 2 or 3 or 'n' grounds. you can have spurious voltage flow from ground rod to ground rod via the path between them in the event of a lightning strike which can then destroy electronics and/or start fires or worse.
      And you are misrepresenting the principle of "single point grounding" which says that you can have multiple electrodes forming a single Ground Electrode System but only bond it to the EGC system (also distributed) at one point. That is what prevents earth currents from flowing in the EGC net. Not having only one electrode.
      Any system which connects an isolated ground rod directly to a local EGC does create the risk you describe, but the NEC does not currently prohibit such designs.

      The NEC does not require single point grounding (it is a design choice) but the only place (2017) explicitly specifies multiple ground electrode connections to the EGC net is for separate buildings.
      Some have expressed reservations about that design too, but it is not as egregious as the "auxiliary electrode" required by the ill fated 690.47(D).
      SunnyBoy 3000 US, 18 BP Solar 175B panels.

      Comment


      • #33
        Originally posted by inetdog View Post

        And you are misrepresenting the principle of "single point grounding" which says that you can have multiple electrodes forming a single Ground Electrode System but only bond it to the EGC system (also distributed) at one point. That is what prevents earth currents from flowing in the EGC net. Not having only one electrode.
        Any system which connects an isolated ground rod directly to a local EGC does create the risk you describe, but the NEC does not currently prohibit such designs.

        The NEC does not require single point grounding (it is a design choice) but the only place (2017) explicitly specifies multiple ground electrode connections to the EGC net is for separate buildings.
        Some have expressed reservations about that design too, but it is not as egregious as the "auxiliary electrode" required by the ill fated 690.47(D).
        inetdog was paraphrasing what was said in the video. after reading it a 2nd time it seems he is referring to an office park scenario. mike was using a residential example. don't really see how the distributed comment pertains in the residential.

        here is the quote from mike in the video: 'bond everything together and then connect to the earth at one point'. he is talking about auxiliary electrodes (an auxiliary electrode may cause equipment failures by providing a path for lightning to travel through equipment) in a residential setting.

        so perhaps we are unintentionally 'talking around' each other.

        Comment


        • #34
          Think of all ground electrode conductors tied directly together as being "earth". The problem with the auxiliary electrode is that it doesn't tie directly into that "earth", but instead a separate electrode in soil that could provide a current path to that "earth" via the panel frames, rail, inverter ECG connection, and AC panel ground bar. So don't ever float an electrode/rod that doesn't connect directly into the overall GEC interconnected system, with solar or medical equipment, residential or commercial.

          Comment


          • #35
            Originally posted by adoublee View Post
            Think of all ground electrode conductors tied directly together as being "earth". The problem with the auxiliary electrode is that it doesn't tie directly into that "earth", but instead a separate electrode in soil that could provide a current path to that "earth" via the panel frames, rail, inverter ECG connection, and AC panel ground bar. So don't ever float an electrode/rod that doesn't connect directly into the overall GEC interconnected system, with solar or medical equipment, residential or commercial.
            with this note, then what about a system with solar array employing a sub-panel from the main box in which the ground wire is not present, only 240ac (3-wire)?

            Comment


            • #36
              Originally posted by inetdog View Post
              And if I have misstated anything above, I am sure Sunking will correct me.
              Nope you got it. Mike summed it up pretty good and if you use these 3 thoughts gets you going in the right direction.

              1. Bond everything together below dirt. This is called your Ground Electrode System. (GES)

              2. Bond everything above dirt together. These are called equipment bonding conductors (EBC), They use to be called equipment grounding conductors (EGC) or the third green wire in your 3-conductor power cords.

              3. Bond 1 and 2 together at only 1 place. This wire is called Ground Electrode Conductor (GEC)

              Use that mental picture and you are off to a good start.


              Last edited by Sunking; 05-26-2017, 10:54 AM.
              MSEE, PE

              Comment


              • #37
                Originally posted by inetdog View Post
                The NEC does not require single point grounding (it is a design choice) but the only place (2017) explicitly specifies multiple ground electrode connections to the EGC net is for separate buildings.
                Some have expressed reservations about that design too, but it is not as egregious as the "auxiliary electrode" required by the ill fated 690.47(D).
                Dave you are absolutely correct, but the NEC has two options for detached buildings or structures. That option the NEC provides is to treat the Feeder to the detached structure like a Service. You do not run an EBC with the Circuit Conductors. Instead you drive your two ground rods together to make a GES and bond it via a GEC to the Grounded Circuit Conductor just like you do any service entrance. Certain conditions must be met, but it is an options and a dang good one. Lot of ham radio operators uses this option on detached ham shacks. Kind of a Poor Man's Isolation Transformer without the Isolation. Keeps lightning where it should be kept and not backing up into the house to find dirt.

                So running a EBC to the detached structure is not required. There is only one catch, that condition I referred to. There cannot be any metallic connection between the two structures like a water pipes, conduit, ect... Easy enough to avoid, and if there is say a water pipe or conduit just use an Isolation Bushing, or if new construction is just a matter of design by using PVC.

                Last word is John Wiles is an advocate of solar. He is a college professor, and like most academics has no real world experience. He wrote 690, and his advocacy although well intentioned has failed and made solar dangerous. The whole point is 690.47 made it a lot less expensive to implement. The issue it is extremely dangerous as Mike Holt spent a 30 minute rant. I know, I was there when he made the video at a hotel conference room during a NEC Conference. It is not news to any pros. Fortunately most AHJ has amended that requirement out, but it will be removed. The sad part, and I feel for him because John Wiles is a friend of mine, John now knows the error of his ways, and knows he has Blood On His Hands and solely responsible for it.

                John was told it would get people killed and damage property and equipment. He did not believe it, his advocacy and lack of real world experience blinded him. Between manufactures of solar equipment, the solar special interest groups coupled with ignorance of some working groups who do not have electrical training and experience, John was able to lobby the NEC voting body to adopting 690.47D. He now has to live with that guilt the rest of his life.

                If any of you know anything about Mike Holt, his video was way out of character. He has never ever demonstrated such strong feelings and emotions. Completely out of character. Well except when he was a young man, dropped out of high school, and a gang banger.
                Last edited by Sunking; 05-26-2017, 12:31 PM.
                MSEE, PE

                Comment


                • #38
                  Originally posted by Sunking View Post

                  Dave you are absolutely correct, but the NEC has two options for detached buildings or structures. That option the NEC provides is to treat the Feeder to the detached structure like a Service. You do not run an EBC with the Circuit Conductors. Instead you drive your two ground rods together to make a GES and bond it via a GEC to the Grounded Circuit Conductor just like you do any service entrance. Certain conditions must be met, but it is an options and a dang good one. Lot of ham radio operators uses this option on detached ham shacks. Kind of a Poor Man's Isolation Transformer without the Isolation. Keeps lightning where it should be kept and not backing up into the house to find dirt.

                  So running a EBC to the detached structure is not required. There is only one catch, that condition I referred to. There cannot be any metallic connection between the two structures like a water pipes, conduit, ect... Easy enough to avoid, and if there is say a water pipe or conduit just use an Isolation Bushing, or if new construction is just a matter of design by using PVC.

                  Last word is John Wiles is an advocate of solar. He is a college professor, and like most academics has no real world experience. He wrote 690, and his advocacy although well intentioned has failed and made solar dangerous. The whole point is 690.47 made it a lot less expensive to implement. The issue it is extremely dangerous as Mike Holt spent a 30 minute rant. I know, I was there when he made the video at a hotel conference room during a NEC Conference. It is not news to any pros. Fortunately most AHJ has amended that requirement out, but it will be removed. The sad part, and I feel for him because John Wiles is a friend of mine, John now knows the error of his ways, and knows he has Blood On His Hands and solely responsible for it.

                  John was told it would get people killed and damage property and equipment. He did not believe it, his advocacy and lack of real world experience blinded him. Between manufactures of solar equipment, the installers, and ignorance of some working groups who do not have electrical training and experience, John was able to lobby the NEC voting body to adopting 690.47D. He now has to live with that guilt the rest of his life.
                  On Mr. Wiles' actions: Maybe a good example of why it's better to have a balance and thorough grounding in both the academic/theoretical and the practical world. It's been my experience that each outlook is more informed and safer when the both are present.

                  Comment


                  • #39
                    i was confused about grounding the pv array in the transformer inverter scenario. i believed that either -d/c or +d/c was required to be 'directly grounded' and that this would be connected in common with the a/c ground. reconciling this was causing me severe problems. this is an easy conclusion to reach absent any sufficiently detailed schematic drawings on the installation and wiring of the array and transformer inverter.

                    so, thanks for helping clear this up. it seems to me that the answer to my question is YES. a transformer inverter with AFCI and GFCI will do just fine.

                    Comment


                    • #40
                      Originally posted by J.P.M. View Post

                      On Mr. Wiles' actions: Maybe a good example of why it's better to have a balance and thorough grounding in both the academic/theoretical and the practical world.
                      Yes sir, I find most academics, and teachers for that matter cannot make i tin the real world and why they teach or politics I would have had to take a serious pay cut if I were Phd or teaching. John is really a great guy, he taught me most everything I know about solar. He is the Grandfather of off-grid solar and where all the industries practices come from. He just cannot put them to real use with his limited electrical background. It took us 2 years to until he finally understood. Well really it took homes burning down and the Pushback AHJ's amending 690.47D out of their local codes. AHJ have the right to adopt the code as written or amend anything out or put in whatever they want.

                      Once good example recently was Arc Fault Circuit Interrupters aka AFCI requirements. That pissed off a lot of people and equipment manufactures and was for pure monetary gain and lobbying. Yes NFPA is political in nature. Again the intent was right, timing was political. One company developed AFCI, and one company only got it shoved in code cycle 1999 and became mandatory in 2002 code cycle. Took a couple of years for UL to buy in. As you can imagine the reason a certain manufacture wanted it pushed through as they were the ole supplier with a UL certification. The politics of NEC got it through. As yo may know the voting members come from all walks of life, and a large portion are non technical and life safety folks like Insurance companies, fire dept, AHJ, UL, and other like groups. A certain manufacture lobbied those groups to get the vote through.

                      Then the Pushback came from electricians and AHJ's loosing a lot of money because they could not get jobs because it required them to use very expensive breakers that were faulty from the start. Fortunately AHJ's just like 690.47D amended them out until more manufactures had products to offer, bring the price down, and worked out the bugs.

                      That is how the game is played. Fortunately we have folks like Mike Holt his team of moderators, and 100,000 plus members that carry a BIG STICK and can get very loud and vocal come conference time. Mike can deliver literally a stack of paper 10 feet high in opposition or favor of code changes, and we get attention. 100,000 sparkies and train drivers can make a lot of noise.
                      MSEE, PE

                      Comment


                      • #41
                        kinda like the EPA geniuses that designed the gas can safety spout - these 'guidelines' were supposed to save lives - to keep people from turning the gas can over their bodies and committing suicide. WTF? all you have to do is remove the nozzle and douse the body with gas and 'flame on' johnny!

                        Comment


                        • #42
                          Originally posted by Jest Waitn View Post
                          kinda like the EPA geniuses that designed the gas can safety spout - these 'guidelines' were supposed to save lives - to keep people from turning the gas can over their bodies and committing suicide. WTF? all you have to do is remove the nozzle and douse the body with gas and 'flame on' johnny!
                          No, that has nothing to do with the gas can rules. They were intended to prevent evaporation of gas and keep kids from getting into the can, not to "keep people from turning the gas can over their bodies and committing suicide." (They are still a pain in the ass though.)
                          Last edited by jflorey2; 05-26-2017, 06:56 PM.

                          Comment


                          • #43
                            And they make you want to remove the nozzle, defeating the purpose. I'm a patient person but life's too short to stand there supporting a 5 gallon jug of gas for 10 minutes while it dribbles out. jiggle hose all the way! Now that's a great invention.
                            2.2kw Suntech mono, Classic 200, NEW Trace SW4024

                            Comment


                            • #44
                              Originally posted by littleharbor View Post
                              And they make you want to remove the nozzle, defeating the purpose. I'm a patient person but life's too short to stand there supporting a 5 gallon jug of gas for 10 minutes while it dribbles out.
                              Yeah, I just made a spout with a 12 inch length of 1" ID vinyl tubing. Worked fine.

                              Comment


                              • #45
                                Well fact be known the recent change in gas cans (2012) has nothing to do with EPA. It has to do with Ambulance chasing Lawyers suing the largest Gas Can (Blitz) a company in Miami OK into bankruptcy. Some idiot kids did not know it could be dangerous throwing gasoline onto a camp fire out of a gas can. When they did that, the fire baked up into the can and exploded. The kids got what they asked for. Guess their parents did not teach them not to play with fire and gasoline.

                                Three lawyers put Blitz out of biz and sent 60 people to the unemployment line.

                                NPR Story Here
                                Last edited by Sunking; 05-26-2017, 11:51 PM.
                                MSEE, PE

                                Comment

                                Working...
                                X